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DGIWG 116-1
Elevation Surface Model Standardized Profile
Document type: Standard
Document date: 10 June 2014
Edition: 1.0.1
Responsible Party: DGIWG
Audience: Approved for public release
Abstract: This Elevation Surface Model standardized profile specifies a content model for geospatial elevation surface data of any spatial resolution. It supports the modelling of material surfaces such as bare earth, vegetation canopy, and bathymetric surfaces
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This is a human-readable summary of the Legal Code (the full license is available from Creative Commons ).
Submitting organizations
France, Sweden, Czech Republic, United Kingdom, and USA
Revision history
DateReleasePrimary clauses modifiedDescription05/31/20090.1AllInitial version submitted for nation review and comment.3/11/20100.2All2nd draft based on DGIWG initial review comment resolution.10/15/20100.3All3rd draft for Technical Panel discussion1/10/20110.4
All
4th draft for Technical Panel discussion11/30/20120.4.5
9/Annex DFinal draft to be reviewed by DGIWG D32 (ESM Project Team) and submitted for publication12/18/20120.4.61, 9, Annex EEdits addressing FR and CZ comments on v.0.4.51/28/20130.4.7Final edits addressing comments on 0.4.61/02/20131.0.0Terms 4.1.13 and 4.1.25Final edits with definitions from ISO 19111 and associated notes4/25/20131.0.0Annex EAlignment with DGIWG Metadata Foundation ed.0.6.012/20/20131.0.010.3, Annex ERevision of ESM tiling guidance, 05/23/20141.0.1Annex EAlignment of ESM metadata with final DGIWG Metadata Foundation
Future work
Development of XML schema document based on GMLCOV, and incorporation of the TIN model into the application schema once it is defined as a coverage in GML and GMLCOV (OGC).
Development of Encoding Annexes supporting specific ESM encoding options
Contents
TOC \o "1-2" 1 Scope PAGEREF _Toc390061817 \h 1
2 Conformance PAGEREF _Toc390061818 \h 1
3 Normative References PAGEREF _Toc390061819 \h 1
4 Terms and definitions, and abbreviated terms PAGEREF _Toc390061820 \h 2
4.1 Terms and definitions PAGEREF _Toc390061821 \h 2
4.2 Symbols, notation and abbreviated terms PAGEREF _Toc390061822 \h 8
4.3 Abbreviated terms PAGEREF _Toc390061823 \h 8
5 Applicability and use PAGEREF _Toc390061824 \h 9
6 Elevation Data Structure PAGEREF _Toc390061825 \h 9
6.1 Concept of Coverages PAGEREF _Toc390061826 \h 9
6.2 CV_Coverage PAGEREF _Toc390061827 \h 10
6.3 ESM Coverages PAGEREF _Toc390061828 \h 11
6.4 ESM Collection PAGEREF _Toc390061829 \h 12
6.5 ESM Grids PAGEREF _Toc390061830 \h 13
6.6 ESM Grid Coverage PAGEREF _Toc390061831 \h 14
6.7 ESM Grid Content PAGEREF _Toc390061832 \h 15
6.8 Variable Cell Size Grids PAGEREF _Toc390061833 \h 18
6.9 ESM TIN Coverage PAGEREF _Toc390061834 \h 18
6.10 ESM Point Coverage PAGEREF _Toc390061835 \h 20
6.11 Point Sets PAGEREF _Toc390061836 \h 22
7 Metadata PAGEREF _Toc390061837 \h 22
7.1 Introduction PAGEREF _Toc390061838 \h 22
7.2 Metadata Hierarchy Levels PAGEREF _Toc390061839 \h 22
7.3 Data Interchange PAGEREF _Toc390061840 \h 22
7.4 Metadata Content Requirements PAGEREF _Toc390061841 \h 23
8 Reference Systems PAGEREF _Toc390061842 \h 26
8.1 Types of referencing PAGEREF _Toc390061843 \h 26
8.2 Horizontal reference systems PAGEREF _Toc390061844 \h 26
8.3 Vertical reference systems PAGEREF _Toc390061845 \h 28
9 Spatial Resolution PAGEREF _Toc390061846 \h 28
10 Considerations for Dense Datasets PAGEREF _Toc390061847 \h 30
10.1 Data compaction PAGEREF _Toc390061848 \h 30
10.2 Data compression PAGEREF _Toc390061849 \h 31
10.3 Tiling PAGEREF _Toc390061850 \h 32
11 Encoding Options PAGEREF _Toc390061851 \h 35
Annex A Abstract Test Suites (normative) PAGEREF _Toc390061852 \h 37
A.1 Coverage Type Tests PAGEREF _Toc390061853 \h 37
A.1.1 Continuous Quadrilateral Grid Coverage Test Case PAGEREF _Toc390061854 \h 37
A.1.2 TIN Coverage Test Case PAGEREF _Toc390061855 \h 37
A.1.3 Point Coverage Test Case PAGEREF _Toc390061856 \h 37
A.1.4 Point Set Test Case PAGEREF _Toc390061857 \h 37
A.1.5 Variable Cell Size Grid Test Case PAGEREF _Toc390061858 \h 38
A.2 Metadata Test Suite PAGEREF _Toc390061859 \h 38
A.2.1 Metadata Completeness Test Case PAGEREF _Toc390061860 \h 38
A.2.2 Maximum occurrence Test Case PAGEREF _Toc390061861 \h 39
A.2.3 Data type Test Case PAGEREF _Toc390061862 \h 39
A.2.4 Domain Test Case PAGEREF _Toc390061863 \h 39
A.2.5 Schema Test Case PAGEREF _Toc390061864 \h 39
A.2.6 Tiling Scheme Test Case PAGEREF _Toc390061865 \h 39
A.3 User-defined Extension Metadata Test Suite PAGEREF _Toc390061866 \h 40
A.3.1 Exclusiveness Test Case PAGEREF _Toc390061867 \h 40
A.3.2 Definition Test Case PAGEREF _Toc390061868 \h 40
A.3.3 Metadata Requirement Class Test Case PAGEREF _Toc390061869 \h 40
A.4 Metadata Profiles PAGEREF _Toc390061870 \h 40
A.4.1 Metadata Profiles Test Case PAGEREF _Toc390061871 \h 40
Annex B UML Notation PAGEREF _Toc390061872 \h 41
B.1 UML notations PAGEREF _Toc390061873 \h 41
B.2 UML model relationships PAGEREF _Toc390061874 \h 41
B.2.1 Associations PAGEREF _Toc390061875 \h 41
B.2.2 Aggregation PAGEREF _Toc390061876 \h 41
B.2.3 Composition PAGEREF _Toc390061877 \h 42
B.2.4 Generalization PAGEREF _Toc390061878 \h 42
B.2.5 Realization PAGEREF _Toc390061879 \h 42
B.2.6 Instantiation / Dependency PAGEREF _Toc390061880 \h 42
B.2.7 Roles PAGEREF _Toc390061881 \h 42
B.3 UML model stereotypes PAGEREF _Toc390061882 \h 43
B.4 Package abbreviations PAGEREF _Toc390061883 \h 44
Annex C Quad trees and Morton ordering (Informative) PAGEREF _Toc390061884 \h 45
C.1 Quad tree Structures PAGEREF _Toc390061885 \h 45
C.2 Morton Ordering PAGEREF _Toc390061886 \h 45
Annex D ESM Data Dictionary (normative) PAGEREF _Toc390061887 \h 47
D.1 Data Dictionary Overview PAGEREF _Toc390061888 \h 47
D.2 Codelists PAGEREF _Toc390061889 \h 47
D.3 ESM Data Elements PAGEREF _Toc390061890 \h 48
D.4 Coverage Data Types PAGEREF _Toc390061891 \h 54
Annex E ESM Metadata Specification (normative) PAGEREF _Toc390061892 \h 56
E.1 ESM Metadata Strategy PAGEREF _Toc390061893 \h 56
E.2 ESM Metadata Elements PAGEREF _Toc390061894 \h 56
E.3 ESM Metadata Extension Rules PAGEREF _Toc390061895 \h 65
E.4 Additional Entities, Elements and Codes (O) PAGEREF _Toc390061896 \h 66
E.5 Quality Reporting Requirements PAGEREF _Toc390061897 \h 66
Annex F Error Propagation Estimates PAGEREF _Toc390061898 \h 67
F.1 Introduction PAGEREF _Toc390061899 \h 67
F.2 Required Data Types PAGEREF _Toc390061900 \h 67
F.3 Calculation of Error Covariance Metadata PAGEREF _Toc390061901 \h 69
F.3.1 Metadata Contents PAGEREF _Toc390061902 \h 69
F.3.1.1 Define Regions PAGEREF _Toc390061903 \h 69
F.3.1.2 Provide Cross-Region Systematic Error Covariance Data PAGEREF _Toc390061904 \h 69
F.3.1.3 Provide Random Covariance Data PAGEREF _Toc390061905 \h 71
F.3.1.4 Provide Relative Covariance Data within a Region PAGEREF _Toc390061906 \h 72
F.3.1.5 Error data discussion PAGEREF _Toc390061907 \h 73
F.3.2 Exploitation PAGEREF _Toc390061908 \h 75
F.3.2.1 Reconstruction of Full Covariance Matrix for a Single Point PAGEREF _Toc390061909 \h 76
F.3.2.2 Reconstruction of Full Covariance Matrix for Multiple Points PAGEREF _Toc390061910 \h 76
F.3.2.2.1 Construct Covariance Matrix for Relative Error PAGEREF _Toc390061911 \h 76
F.3.2.2.2 Random Error Covariance at a Point PAGEREF _Toc390061912 \h 77
F.3.2.2.3 Computing the Absolute Error at a Point PAGEREF _Toc390061913 \h 77
Annex G Use Case Analysis (Informative) PAGEREF _Toc390061914 \h 80
G.1 Introduction PAGEREF _Toc390061915 \h 80
G.2 Initial Scope PAGEREF _Toc390061916 \h 80
G.3 Use Case Guidelines PAGEREF _Toc390061917 \h 80
G.4 Illustrative Use Cases PAGEREF _Toc390061918 \h 81
Bibliography PAGEREF _Toc390061919 \h 82
Figures
TOC \h \z \t "Caption" \c HYPERLINK \l "_Toc389813373" Figure 1 - Height PAGEREF _Toc389813373 \h 6
HYPERLINK \l "_Toc389813375" Figure 2 - CV_Coverage PAGEREF _Toc389813375 \h 11
HYPERLINK \l "_Toc389813377" Figure 3 - ESM Collection PAGEREF _Toc389813377 \h 13
HYPERLINK \l "_Toc389813378" Figure 4 - An example of a quadrilateral grid PAGEREF _Toc389813378 \h 13
HYPERLINK \l "_Toc389813379" Figure 5 - ESM Grid Coverage PAGEREF _Toc389813379 \h 14
HYPERLINK \l "_Toc389813381" Figure 6 - ESM Grid PAGEREF _Toc389813381 \h 16
HYPERLINK \l "_Toc389813382" Figure 7 - Example TIN Triangles PAGEREF _Toc389813382 \h 19
HYPERLINK \l "_Toc389813383" Figure 8 - ESM TIN Coverage PAGEREF _Toc389813383 \h 19
HYPERLINK \l "_Toc389813384" Figure 9 ESM Point Coverage PAGEREF _Toc389813384 \h 21
HYPERLINK \l "_Toc389813386" Figure 10 General Interchange Organization PAGEREF _Toc389813386 \h 23
HYPERLINK \l "_Toc389813387" Figure 11 - Example of UTM Point Location In Northern Hemisphere PAGEREF _Toc389813387 \h 28
HYPERLINK \l "_Toc389813391" Figure 13 - Tiling Schemes PAGEREF _Toc389813391 \h 32
HYPERLINK \l "_Toc389813392" Figure 14 - Quadrant Numbering PAGEREF _Toc389813392 \h 33
HYPERLINK \l "_Toc389813393" Figure 15 - Shared Values at Tile Edges. PAGEREF _Toc389813393 \h 34
HYPERLINK \l "_Toc389813394" Figure 16 - Discontinuity at Tile Edge. PAGEREF _Toc389813394 \h 34
HYPERLINK \l "_Toc389813395" Figure 12 ESM Tiling (Informative) PAGEREF _Toc389813395 \h 35
HYPERLINK \l "_Toc389813396" Figure B.1 UML Associations PAGEREF _Toc389813396 \h 41
HYPERLINK \l "_Toc389813397" Figure B.2 UML Class Relationships PAGEREF _Toc389813397 \h 43
HYPERLINK \l "_Toc389813398" Figure C.1 Morton Ordering PAGEREF _Toc389813398 \h 46
HYPERLINK \l "_Toc389813399" Figure C.2 Morton Ordering in an Irregular Grid PAGEREF _Toc389813399 \h 46
HYPERLINK \l "_Toc389813410" Figure F.1 Example Covariance Matrix Data Needed for Rigorous Error Propagation. PAGEREF _Toc389813410 \h 69
HYPERLINK \l "_Toc389813411" Figure F.2 Full Covariance Data for the Systematic Errors of Four Regions PAGEREF _Toc389813411 \h 71
HYPERLINK \l "_Toc389813412" Figure F.3 Systemati c E r r o r ( G , R # ) p e r R e g i o n P A G E R E F _ T o c 3 8 9 8 1 3 4 1 2 \ h 7 1
H Y P E R L I N K \ l " _ T o c 3 8 9 8 1 3 4 1 3 " F i g u r e F . 4 T h e R a n d o m E r r o r ( R ) a t a P o i n t ( P ) P A G E R E F _ T o c 3 8 9 8 1 3 4 1 3 \ h 7 2
H Y P E R L I N K \ l " _ T o c 3 8 9 8 1 3 4 1 4 " F i g u r e F . 5 R e l a t i v e C o v a r i a n c e o f V e c t o r R Within a Region PAGEREF _Toc389813414 \h 73
HYPERLINK \l "_Toc389813415" Figure F.6 Systematic and Random Error Vector Representation PAGEREF _Toc389813415 \h 74
HYPERLINK \l "_Toc389813416" Figure F.7 Sample DEM Footprint Consisting of Four Regions with Vector Crossing Regions PAGEREF _Toc389813416 \h 76
HYPERLINK \l "_Toc389813417" Figure F.8 Covariance Data at a Point PAGEREF _Toc389813417 \h 77
HYPERLINK \l "_Toc389813418" Figure F.9 Horizontal Error Ellipse at a Point PAGEREF _Toc389813418 \h 78
HYPERLINK \l "_Toc389813419" Figure F.10 Circular Error from Covariance Data PAGEREF _Toc389813419 \h 79
Tables
TOC \h \z \c "Table" HYPERLINK \l "_Toc389814939" Table 1 - Sources of externally defined UML classes PAGEREF _Toc389814939 \h 8
HYPERLINK \l "_Toc389814940" Table 2 - Elevation Grid Resolution Levels for Projected Data (Informative) PAGEREF _Toc389814940 \h 29
HYPERLINK \l "_Toc389814941" Table 3 - Elevation Grid Resolution Levels for Data Referenced to WGS84 Geographic Coordinates (Informative) PAGEREF _Toc389814941 \h 29
HYPERLINK \l "_Toc389814942" Table 4 - NATO Resolution Levels for Geospatial Information PAGEREF _Toc389814942 \h 30
HYPERLINK \l "_Toc389814943" Table D.1 - ESM Codelists PAGEREF _Toc389814943 \h 47
HYPERLINK \l "_Toc389814944" Table D.2 - CV_Coverage (Figure 2) PAGEREF _Toc389814944 \h 49
HYPERLINK \l "_Toc389814945" Table D.3 - ESM Collection (Figure 3) PAGEREF _Toc389814945 \h 51
HYPERLINK \l "_Toc389814946" Table D.4 - ESM Grid Coverage (Figure 5) PAGEREF _Toc389814946 \h 52
HYPERLINK \l "_Toc389814947" Table D.5 ESM Grid (Figure 6) PAGEREF _Toc389814947 \h 53
HYPERLINK \l "_Toc389814948" Table D.6 - ESM Grid Values (Figure 6) PAGEREF _Toc389814948 \h 54
HYPERLINK \l "_Toc389814949" Table D.7 - Coverage Sequence Rule (Figure 6) PAGEREF _Toc389814949 \h 54
HYPERLINK \l "_Toc389814950" Table D.8 - Coverage Grid Envelope (Figure 6) PAGEREF _Toc389814950 \h 55
HYPERLINK \l "_Toc389814951" Table D.9 - Coverage Grid Coordinate (Figure 6) PAGEREF _Toc389814951 \h 55
HYPERLINK \l "_Toc389814952" Table E.1 - ESM Core Metadata PAGEREF _Toc389814952 \h 57
Introduction
This profile standardizes the information content required for the exchange of surface elevation information within and among DGIWG member nations. It specifies a data model that may be used to describe a variety of surfaces including bare earth, vegetation canopy, and bathymetric depth. Digital Terrain Elevation Data (DTED) has been the predominant format for defense community elevation products with post spacings of 30m and larger. DTED is a product with a specific encoding format that is incapable of adequately depicting the higher resolution data collected by new elevation data sensors. Many defense applications now require this data, and newer encoding formats are available that are capable of carrying additional information about the data. The new capabilities allowed by the standardisation of the information content of the datasets will improve discovery, interoperability, and exploitation of the data.
The intent is to increase the level of interoperability with and between organizations producing and using elevation data. The data model is applicable to a variety of spatial resolutions and accuracies and it specifies the elevation data content separately from the encoding method.
To attain maximum flexibility for exchange of surface elevation data, this standardized profile identifies a large set of metadata elements that may be used to describe a variety of types of elevation datasets. It may be used to generate specifications for narrowly defined products by specifying fixed values in place of the range of metadata values allowed here.
This profile is based on relevant standards established by the International Organization for Standardization (ISO) for geographic information, and, where applicable, for information technology. It is consistent with the International Hydrographic Organization (IHO) Universal Hydrographic Data Model (S-100).
ISO 19123 defines a conceptual schema for the spatial characteristics of coverages. Coverages support mapping from a spatiotemporal domain to attribute values where attribute types are common to all geographic positions within the spatiotemporal domain. The concept of coverages provides a more flexible way to describe elevation data as mathematical surfaces, in a manner that can be easily integrated with other types of geographic information or with other coverage data.
An application schema is the conceptual schema for data (e.g. elevation data) required by one or more applications. ISO 19129 includes the concept of a content model as the information view of an application schema. This view includes descriptions of the elements composing the domain object (grid, TIN, points, etc.), the corresponding range values, the spatial referencing, and associated metadata of various types. A content model addresses only the information needed to describe the semantic meaning of the data, exclusive of the interchange format or portrayal of the data.
The DGIWG Metadata Foundation (DMF) defines a comprehensive list of metadata elements for geospatial data. It is based on NATO STANAG 2586, the NATO Geospatial Metadata Profile (NGMP). DMF is also based on the ISO 19115 standards for geographic metadata. These standards form the basis of the ESM metadata requirement. They are extended where necessary with metadata elements describing particular aspects of elevation surface data, and addressing specific requirements of the defense community.
This standardized profile is concerned with both the underlying information structure of an elevation surface model and the format for exchanging elevation surface models. However, defining the content in terms of its encoding binds the content to that single encoding format and makes format conversion difficult. This profile allows for a variety of encoding formats to be used to carry the elevation data values, and the common content model described in this profile allows for a mapping to the structures defined in the various encoding standards. Within the metadata, descriptions of elevation datasets could vary based on the interpretation of metadata producers, and interoperability is primarily supported through the requirement for XML-encoded metadata. ISO XML schemas provide a definitive, rule-based encoding for validation of DMF and ESM metadata requirements.
Elevation Surface Model
Scope
Elevation measurements describe the position of the material surface above or below a vertical datum. This Elevation Surface Model (hereafter ESM) standardized profile specifies a content model for geospatial elevation surface data of any spatial resolution. It supports the modelling of material surfaces such as bare earth, vegetation canopy, and bathymetric surfaces. Four optional data structures are described: grids, Triangulated Irregular Networks (TIN), point coverages, and point sets. The grid, TIN and point coverage structures are defined by the ISO 19123:2005 coverage geometry classes CV_ContinousQuadrilateralGridCoverage, CV_TINCoverage, and CV_DiscretePointCoverage. The geometry for ESM point sets is provided by the GM_Point class, defined in ISO 19107. These structures are the most commonly stored and exchanged by systems managing elevation data. While it is acknowledged that coverages can be derived from a collection of discrete features (and vice versa), other discrete data elements (e.g. contour lines) are not specifically addressed by this profile.
Conformance
The degree to which an elevation data product specification complies with the content models defined in this profile can be measured using an abstract test suite. Any data or product specification claiming conformance with this profile shall pass all requirements described in the abstract test suite provided in Annex A.
Normative References
The following normative documents contain provisions that, through reference in this text, constitute provisions of this profile.
International Standards
ISO 639-2:1998 Codes for the representation of names and languages
ISO/TS 19103:2005 Geographic information - Conceptual schema language
ISO 19107:2003 Geographic information Spatial schema
ISO 19108:2002/Cor 1:2006 Geographic information Temporal schema
ISO 19109:2003 Geographic information Rules for application schema
ISO 19111:2007 Geographic information Spatial referencing by coordinates
ISO 19115:2003 Geographic information Metadata
ISO 19115/Cor.1:2006 Geographic information Metadata Technical Corrigendum 1
ISO 19115-2:2009 Geographic information - Metadata: Extensions for imagery and gridded data
ISO 19123:2005 Geographic information - Schema for coverage geometry and functions
ISO 19129:2008 Geographic information Imagery, gridded and coverage data framework
ISO 19138:2006 Geographic information Data quality measures
ISO 19139:2006 Geographic information Metadata XML schema implementation
IHO S-100 edition 1.0.0 Hydrographic Geospatial Standard for Marine Data and Information
NATO MC 0296/2, NATO Geospatial Policy, IMSTAM (GE0)-0001-2010 (SD3) dated 27 September 2010
STANAG 2215 IGEO (Edition 7, July 2010) Evaluation of Land maps, Aeronautical charts and Digital Topographic data
DGIWG - 114: DGIWG Metadata Foundation (STD-DP-12-010), 13 November 2013
National Standards
DMA TR 8400.1: Error Theory as Applied to Mapping, Charting and Geodesy. US Defense Mapping Agency. 2 May 1991
NIMA TR 8350.2, Third Edition, Amendment 1: Department of Defense World Geodetic System 1984; Its Definition and Relationships with Local Geodetic Systems. National Imagery and Mapping Agency. 3 January 2000
NIMA TM 8358.2: The Universal Grids: Universal Transverse Mercator (UTM), Universal Polar Stereographic (UPS). September 1989
Terms and definitions, and abbreviated terms
Terms and definitions
Terms and definitions have been taken from the references cited in the Normative References (section 3) and the Bibliography.
absolute accuracy
closeness in position of reported coordinate values to true values or values accepted as being true. Also referred to as external accuracy.
[ISO 19113]
aggregation
a form of association that specifies a whole-part relationship between the aggregate (whole) and a constituent part
[ISO 19103]
class
description of a set of objects that share the same attributes, operations, methods, relationships, and behavior
[ISO 19103]
continuous coverage
coverage that returns different values for the same feature attribute at different direct positions within a single spatial object, temporal object, or spatiotemporal object in its domain
[ISO 19123]
coordinate
one of a sequence of numbers designating the position of a point in N-dimensional space
[ISO 19111]
coordinate reference system
coordinate system which is related to the real world by a datum
[ISO 19111]
coverage
feature that acts as a function to return values from its range for any direct position within its spatial, temporal, or spatiotemporal domain
[ISO 19123]
EXAMPLE Examples include a digital image, polygon overlay, or digital elevation matrix.
NOTE In other words, a coverage is a feature that has multiple values for each attribute type, where each direct position within the geometric representation of the feature has a single value for each attribute type.
coverage geometry
configuration of the domain of a coverage described in terms of coordinates
[ISO 19123]
data compaction
reduction of the number of data elements, bandwidth, cost, and time for the generation, transmission, and storage of data without loss of information by eliminating unnecessary redundancy, removing irrelevancy, or using special coding
[ANSI T1.523-2001]
NOTE Whereas data compaction reduces the amount of data used to represent a given amount of information, data compression does not.
data compression
Reduction in the amount of storage space (bits) required to represent an image or dataset, or reduction in the length of message required to transfer a given amount of information.
[ISO 10918-1]
NOTE Data compression does not reduce the amount of data used to represent a given amount of information, whereas data compaction does. Both data compression and data compaction result in the use of fewer data elements for a given amount of information.
dataset
identifiable collection of data that can be represented in an exchange format or stored on a storage media
NOTE A dataset may be a smaller grouping of data, which though limited by some constraint such as spatial extent or feature type, is located physically within a larger dataset. Theoretically, a dataset may be as small as a single feature or feature attribute contained within a larger dataset. A hardcopy map or chart may be considered a dataset.
[ISO 19115]
dataset series
collection of datasets sharing the same product specification
[ISO 19115]
NOTE The datasets in a series may have been derived from the same sensor or platform, or may adhere to a common product specification. They typically share the same geometry (e.g. grid or TIN).
depth
distance of a point from a chosen reference surface measured downward along a line perpendicular to that surface
NOTE 1 A depth above the reference surface will have a negative value. [ISO 19111]
NOTE 2 Depth is positive if measured downward or inside of the reference surface. Depth is distinguished from height in that it is a directional measurement.
direct position
position described by a single set of coordinates within a coordinate reference system
[ISO 19107]
domain
well-defined set
[ISO 19103]
NOTE Domains are used to define the domain set and range set of operators and functions.
elevation
distance of a point from mean sea level measured along a line perpendicular to the mean sea level surface, positive if upwards or outside of the mean sea level surface.
NOTE Elevation can be expressed as a height above mean sea level or a depth below mean sea level.
evaluation < coverage>
determination of the values of a coverage at a direct position within the spatiotemporal domain of the coverage
[ISO 19123]
feature
abstraction of real world phenomena
[ISO 19101]
feature attribute
characteristic of a feature
[ISO 19109]
NOTE A feature attribute type has a name, a data type and a domain associated to it. A feature attribute instance has an attribute value taken from the value domain of the feature attribute type.
function
rule that associates each element from a domain (source, or domain of the function) to a unique element in another domain (target, co-domain, or range)
[ISO 19107]
NOTE The range is defined by another domain.
geoid
level surface which best fits mean sea level either locally or globally
[ISO 19111]
NOTE Level surface means an equipotential surface of the Earths gravity field which is everywhere perpendicular to the direction of gravity.
geometric object
spatial object representing a set of direct positions
[ISO 19107]
NOTE A geometric object consists of a geometric primitive, a collection of geometric primitives, or a geometric complex treated as a single entity. A geometric object may be the spatial characteristics of an object such as a feature or a significant part of a feature.
grid
network composed of two or more sets of curves in which the members of each set intersect the members of the other sets in a systematic way
[ISO 19123]
NOTE The curves partition a space into grid cells.
grid point
point located at the intersection of two or more curves in a grid
[ISO 19123]
height
distance of a point from a chosen reference surface measured upward along a line perpendicular to that surface
NOTE A height below the reference surface will have a negative value.
4.1.25.1 ellipsoidal height (h)
distance of a point from the ellipsoid surface measured upward along a line perpendicular to the ellipsoid, positive if upwards or outside of the ellipsoid. Also known as geodetic height.
NOTE Only used as part of a three-dimensional coordinate system and never on its own.
4.1.25.2 gravity-related height (H)
Height dependent on the Earths gravity field
NOTE In particular, orthometric height or normal height, which are both approximations of the distance of a point above the mean sea level.
4.1.25.3 geoid height (N)
distance of a point on the geoid from the ellipsoid surface measured upward along the line perpendicular to the ellipsoid, positive if above the ellipsoid.
[ISO 19111]
NOTE 1 The reference surface is based on the geoid and may be approximated by an ellipsoid or hydrographic surface. Height is distinguished from elevation in that it is a directional measurement. A height below the reference surface will have a negative value. Negative height is also called depth. This definition also applies to altitude.
NOTE 2 Ellipsoidal height = gravity-related (orthometric) height + geoid height
Figure 1 - Height
point
0-dimensional geometric primitive, representing a position within a coordinate reference system
[ISO 19107]
point coverage
coverage that has a spatial domain composed of points
[ISO 19123]
point set
a set of vertices in a three-dimensional coordinate system. These vertices are usually represented by easting, northing, and height values.
[derived from ISO 19123]
post
The locations of the intersections of rows and columns within an elevation grid. Post spacing for a rectified grid is a measure of its horizontal resolution
[derived from NATO STANAG 3809: DTED]
quad tree
expression of a two-dimensional object as a tree structure of quadrants, which are formed by recursively subdividing each non-homogeneous quadrant until all quadrants are homogeneous with respect to a selected characteristic, or until a predetermined cut-off depth is reached
[ISO 2382]
range
set of feature attribute values associated by a function with the elements of the domain of a coverage
[ISO 19123]
record
finite, named collection of related items (objects or values)
[ISO 19107]
NOTE Logically, a record is a set of pairs .
rectified grid
grid for which there is an affine transformation between the grid coordinates and the coordinates of an external coordinate reference system
[ISO 19123]
NOTE If the coordinate reference system is related to the earth by a datum, the grid is a georectified grid.
relative accuracy
closeness of the relative positions of features in a dataset to their respective relative positions accepted as or being true
[ISO 19113]
spatiotemporal domain
domain composed of spatiotemporal objects
[ISO 19123]
NOTE The spatiotemporal domain of a continuous coverage consists of a set of direct positions defined in relation to a collection of geometric objects.
surface
connected 2-dimensional geometric object, locally representing the continuous image of a region of a plane
[ISO 19107]
NOTE The boundary of a surface is the set of oriented, closed curves that delineate the limits of the surface.
tessellation
partitioning of a space into a set of conterminous geometric objects having the same dimension as the space being partitioned
[ISO 19123]
NOTE A tessellation composed of congruent regular polygons or polyhedra is a regular tessellation; One composed of regular, but non-congruent polygons or polyhedra is semi-regular. Otherwise, the tessellation is irregular.
Tile
A rectangular array of points on the reference grid, registered with and offset from the reference grid origin and defined by a width and height
[ISO/IEC 15444-1]
triangulated irregular network (TIN)
tessellation composed of triangles
[ISO 19123]
vector
quantity having direction as well as magnitude
[ISO 19123]
NOTE A directed line segment represents a vector if the length and direction of the line segment are equal to the magnitude and direction of the vector. The term vector data refers to data that represents the spatial configuration of features as a set of directed line segments.
Symbols, notation and abbreviated terms
In this Profile, conceptual schemas are presented in the Unified Modelling Language (UML). An overview of the use of UML in geographic information standards is provided in ISO 19103, and Annex B of this profile provides a guide to UML notation. The UML models provided in this document are available separately from DGIWG D32 at HYPERLINK "http://portal.dgiwg.org/files/?artifact_id=8471" http://portal.dgiwg.org/files/?artifact_id=8471.
Most of the model elements used in the schema defined in this profile are derived from ISO standards developed by ISO Technical Committee 211 (Geographic Information/Geomatics), which has provided a naming convention that assigns a unique two-character prefix to a class of data to identify the package and standard from which it comes. UML Object Constraint Language (OCL) is used to explicitly document all constraints. The implementations of ISO classes defined by this profile are given the prefix ESM.
Table SEQ Table \* ARABIC \s 1 1 - Sources of externally defined UML classes
PrefixStandardPackage-ISO 19103Basic TypesCIISO 19115Citation and responsible party informationCVISO 19123CoverageDSISO 19115DatasetEXISO 19115Extent informationFCISO 19110Feature CatalogueGFISO 19109General feature modelGMISO 19107Geometric primitiveLIISO 19115Lineage informationMDISO 19115MetadataMIISO 19115-2Imagery MetadataMXISO 19139 Metadata for Data InterchangeSCISO 19111Spatial Ref by CoordinatesRSISO 19115Reference system informationTMISO 19108Temporal schema
Abbreviated terms
BIIF Basic Imagery Interchange Format Standard (ISO/IEC 12087-5)
DEM Digital Elevation Model
DTED Digital Terrain Elevation Data
ESM Elevation Surface Model
GeoTIFF Geographic Tagged Image File Format
GML Geography Markup Language
HDF5 Hierarchical Data Format Version 5
IHO International Hydrographic Organization
ISO International Organization for Standardization
JPEG Joint Photographic Experts Group
NATO North Atlantic Treaty Organization
NITF National Imagery Transmission Format
NSIF NATO Secondary Imagery Format
TIN Triangulated Irregular Network
TRE Tagged Record Extension (of NITF / NSIF)
UML Unified Modelling Language
UTM Universal Transverse Mercator
XML eXtensible Markup Language
Applicability and use
This profile is applicable to the exchange of elevation surface data. It does not specify how such data is to be collected or used, but provides a common elevation data model to Defense communities. This common underlying model, based on international standards, permits the implementation of a concept of operations in which multiple producers and multiple users exchange elevation surface data. A common content model is provided, defining the minimum information required for the exchange and effective use of elevation data. The content model is independent of the encoding format and will serve as the basis for an ESM Application Schema. Compliance with the ESM content model will allow exchange of elevation data in user-specified encoding formats. The ESM Profile is also intended to result in a higher degree of interoperability across user domains and support the requirement for greater level of detail and quality reporting in elevation datasets.
Elevation Data Structure
Concept of Coverages
Elevation data is relatively simple data. It consists of a set of elevation values together with metadata that describes the meaning of these values. The elevation values are organized according to a spatial schema. For most types of elevation data, this schema takes the form of a coverage.
The Open Geospatial Consortium developed the coverage concept that is described in ISO 19123. A coverage is defined as a subtype of feature in that it represents real world phenomena in terms of a set of attributes. It acts as a function to return one or more attribute values for any direct position within its spatiotemporal domain. A set of known attribute values associated with specified positions is provided to drive the coverage function. This concept forms the basis of this standardized profile; however, it does not compromise the inherent simplicity of elevation data. Such data is still primarily a set of elevation values upon which a coverage function can operate.
A continuous coverage returns a distinct attribute value for each position in the domain. Continuous coverages are in effect interpolation functions across a set of data values. The coverage function allows one to interpolate attribute values across the spatiotemporal domain. Elevation models are inherently continuous coverages. The interpolation method to be used is described as part of the metadata associated with a coverage.
A coverage may also be a discrete function that returns a single value over the entire area of a specified element within the domain of the coverage. Discrete coverages are used to represent classification schemes and in other situations where the coverage attributes represent discrete variables. In general, it is not possible to interpolate between the values of a discrete coverage. An elevation point coverage (6.10) is an example of a discrete coverage. Contour line coverages, which are not addressed by this profile, are another example.
One of the advantages of using a coverage approach is that a coverage can include multiple attribute values for each point, so it can be used to represent more than one characteristic of the location represented by the point. However, a coverage cannot be used to represent multiple elevation surfaces. To support the case of multiple surfaces being represented in a single dataset, this standard addresses the point set structure (6.11), in which the elevation of each point is carried as one of its spatial coordinates.
A regular row-column grid of attribute values is not the only way of driving a coverage function. Different types of grids with various traversal orders may be defined. The attribute values may also be organized in other ways such as Triangulated Irregular Networks (TIN) or a point coverages with unstructured sets of Z values at X,Y locations. However, the regular quadrilateral grid is the coverage geometry used for most elevation data. TIN and point data are more useful for some applications. Conversions are possible between grid and TIN descriptions of the same area, and point data may be derived from grids and TINs.
CV_Coverage
The class CV_Coverage (Figure 2) from ISO 19123 is a generalization of the discrete and continuous coverage types. It has three attributes and three associations, and these relationships are inherited by the Elevation coverage classes specified in this profile. The attribute domainExtent describes the spatial and/or temporal extent of the domain coverage. The data type EX_Extent is defined in ISO 19115. The attribute rangeType describes the structure and composition of the attribute data record. The data type RecordType is specified in ISO/TS 19103. The attribute commonPointRule identifies a method for resolving potential conflicts between attribute values resulting from evaluation of a coverage at a direct position when that position falls on the boundary between two value objects, such as two grid cells or two of the triangles in a TIN.
Associated with a CV_Coverage is the specification of the Coordinate Reference System to which the objects in the domain are referenced. Also associated are domain and range specifications. CV_DomainObject represents an element of the domain of the coverage and CV_AttributeValues represents and element from the range of the coverage. In the case of a discrete coverage, the multiplicity of CV_Coverage.rangeElement equals that of CV_coverage.domainElement because there is only one instance of CV_AttributeValues for each instance of CV_DomainObject. For a continuous coverage, there is a transfinite number of instances of CV_AttributeValues for each CV_DomainObject.
Figure 2 - CV_Coverage
ESM Coverages
Introduction
ESM_Coverage (see Figure 3) specifies a set of attributes common to all types of coverages. In this profile only the Grid, Elevation TIN and Elevation Point coverage types are addressed. Point sets (which do not meet the definition of a coverage) are addressed in section 6.11. The class ESM_Coverage is an abstract class that specifies a set of attributes common to all types of coverages that may be contained in an ESM_Collection. ESM_Coverage is a realization of the Type CV_Coverage specified in ISO 19123 and implements attributes for that type. The attributes are domainExtent, rangeType, and commonPointRule.
domainExtent
The attribute domainExtent describes the spatial extent of the domain of the ESM_Coverage. It uses the data type EX_GeographicExtent specified in ISO 19115.
rangeType
The attribute rangeType describes the range of the ESM_Coverage. It uses the data type RecordType specified in ISO/TS 19103. An instance of RecordType is a list of name/datatype pairs, each of which describes an attribute type included in the range of the coverage. The name field shall be used to identify the type of surface that each elevation value describes.
NOTE The definition of the attribute type shall be provided by a feature catalogue.
EXAMPLE For a coverage containing elevation values for bare earth, vegetation canopy, and a radar reflective surface, the attribute types could be described as: "bare earth surface elevation:Real, vegetation canopy surface elevation:Real, radar reflective surface elevation:Real".
commonPointRule
The attribute commonPointRule describes the procedure used for evaluating the ESM_Coverage at a position that falls on the boundary or in an area of overlap between geometric objects in the domain of the coverage. It takes a value from the code list CV_CommonPointRule specified in ISO 19123. The rule shall be applied to the set of elevation values that results from evaluating the coverage with respect to each of the geometric objects that share a boundary. For elevation coverages, the values of the CV_CommonPointRule shall be 'average', 'high', or 'low'. For example, data used for aeronautical purposes might make use of the 'high' value to ensure that vertical obstructions are emphasised.
The use of the commonPointRule occurs where a set of geometric objects are involved, such as the triangles in a TIN.
ESM Collection
An ESM collection (Figure 3) consists of one or more ESM datasets. The datasets in an ESM collection do not necessarily share the same geometry. They might include one or more coverage types or point sets over a specified area. For example, an ESM collection may consist of a grid coverage and a point set over the same area, where the grid coverage represents an elevation surface and the point set a number of more accurately measured elevation points. Alternatively, a collection may consist of multiple coverages of the same type representing different elevation surface types (7.4.2). A dataset series is a type of collection in which the component datasets typically share the same geometry. The datasets in a series may have been derived from the same sensor or platform, or may adhere to a common product specification.
Figure 3 - ESM Collection
ESM Grids
The grid structure is the most common geometric representation for elevation data. The other types can be derived from an elevation grid. A grid is defined by the intersection of two (or more) sets of curves called grid lines and the intersection points are called grid points. The area defined by four adjacent grid points is a grid cell. This standardized profile addresses only quadrilateral grids, in which grid lines are straight and grid cells are parallelograms. There is one set of grid lines for each dimension of space, so in a common two-dimensional grid there are two sets of grid lines. The grid points at the intersections are often referred to as posts in elevation data. Figure 4 illustrates a simple quadrilateral grid.
Figure 4 - An example of a quadrilateral grid
A rectified grid is related to the earth or other reference by an affine transform based on the location of the origin of the grid and the orientation of and spacing along each axis. It is a uniformly spaced grid, so that the location of one cell in a georectified grid can be determined based on another cells location, the cell interval, and the grid orientation.
Georeferencable grids include a coordinate transform that can be used to calculate the location of any cell in the grid, but each cells location must be calculated independently. Georectified gridded data are normally obtained from unrectified data through georectification (also called geometric correction).
This profile is concerned only with rectified quadrilateral grids. Most existing elevation data formats are based on simple rectified quadrilateral grids, which are only a small subset of the grid coverages defined by ISO 19123. The only thing that distinguishes an elevation grid coverage from other quadrilateral grid coverages is that the attributes represent elevation values.
ESM Grid Coverage
ESM Grid Coverage Model
The class ESM_GridCoverage (Figure 5) represents a set of elevation values assigned to the points in a 2-dimensional grid. Several organizations of grids are possible with different grid traversal orders, and variable or fixed grid cell sizes. This standard is concerned with two types of grid organizations, the simple quadrilateral grid (Figure 4) with equal cell sizes traversed by a linear sequence rule, and the variable cell size quadrilateral grid traversed by a Morton Order sequence rule (6.7.8). The variable cell size grid organization is known as the Quad Tree for a two dimensional grid.
Figure 5 - ESM Grid Coverage
ESM Grid Coverage Class
The class ESM_GridCoverage is subclass of ESM_Coverage. It represents the set of values assigned to the points in a 2-dimensional grid. The class is a realization of the type CV_ContinuousQuadrilateralGridCoverage from ISO 19123.
interpolationType
The attribute interpolationType describes the interpolation method recommended for evaluation of the ESM_GridCoverage. For grid coverages, the value shall be nearest neighbour, bilinear, biquadratic, 'bicubic', or a user-defined interpolation. A user-defined interpolation method must be documented in a product specification.
Nearest neighbor interpolation can be applied to any coverage. It generates a feature attribute value at a direct position by assigning it the feature attribute value associated with the nearest domain object in the domain of the coverage. Nearest Neighbor interpolation is generally not recommended for elevation data, although it may produce acceptable results when resampling to generate a grid with much lower resolution than the source grid.
Bilinear interpolation is used to interpolate feature attribute values at direct positions within a quadrilateral grid using the function:
v = a0 +a1x +a2y +a3xy
The following is a common algorithm for this interpolation technique. Given a direct position, p, contained in a grid cell whose vertices are V, V + V1 , V + V2 , and V + V1 + V2 , with feature attribute values at these vertices of W1, W2, W3, and W4, respectively, there are unique numbers i and j, with 0 ( i < 1, and 0 ( j < 1 such that p = V + iV1 + jV2 . The feature attribute value at p is:
W = (1-i)(1-j)W1 + i(1-j)W2 + j(1-i)W3 + ijW4
Biquadratic interpolation is also used to compute feature attribute values at direct positions within a quadrilateral grid. It is based on the assumption that feature attribute values vary as a biquadratic function of position within the grid cell:
v = a0 +a1x +a2y +a3x2 +a4xy + a5y2 + a6x2y + a7xy2 + a8x2y2
ISO 19123 references sources for algorithms for implementing biquadratic interpolation.
Bicubic interpolation is also used to compute feature attribute values at direct positions within a quadrilateral grid. Bicubic interpolation uses the function:
v = a0 +a1x +a2y +a3x2 +a4xy + a5y2 + a6x2y + a7xy2 + a8x2y2 + a9x3 + a10y3 + a11x3y + a12xy3 + a13x3y2 + a14x2y3 + a15x3y3
ISO 19123 references sources for algorithms for implementing bicubic interpolation.
data
The role name data identifies the ESM_Grid that contains the values of the ESM_Coverage.
ESM Grid Content
ESM Grid Model
The class ESM_Grid (Figure 6) represents the data content of an ESM_GridCoverage. It contains the data values as a sequence of records.
Figure 6 - ESM Grid
ESM Grid Class
The class ESM_Grid is a realization of the CV_RectifiedGrid and CV_GridValuesMatrix classes from ISO 19123, and the attributes are inherited from the ISO classes.
dimension
The attribute dimension specifies the dimensionality of the grid.
axisNames
The attribute axisNames specifies the names of the grid axes. Axes are often named for their orientation relative to the external coordinate reference system, with north and east being very common examples.
origin
The attribute origin specifies the coordinates of the grid origin with respect to an external coordinate system. The data type DirectPosition, specified in ISO 19107, has an association through the role name coordinateReferenceSystem to the class SC_CRS (ISO 19111) which specifies the external coordinate reference system (7.4.6).
offsetVectors
The attribute offsetVectors specifies the spacing between grid points and the orientation of the grid axes with respect to the external coordinate reference system identified through the attribute origin. It uses the data type Vector specified in ISO/TS 19103.
extent
The attribute extent specifies the area of the grid for which elevation data are provided. It uses the type CV_GridEnvelope specified in ISO 19123 to provide both the CV_GridCoordinates of the corner of the area having the lowest grid coordinate values and the CV_GridCoordinates of the corner of the area having the highest grid coordinate values. CV_GridCoordinate is specified in ISO 19123.
sequencingRule
The attribute sequencingRule specifies the method to be used to assign values from the sequence of elevation values to the grid coordinates. It uses the data type CV_SequenceRule specified in ISO 19123.
CV_SequenceRule has two attributes. The attribute type identifies the technique used to move from one point to the next. Only the values "linear" and "Morton" shall be used for data that conforms to this standard. Both linear and Morton can be extended to a 3-dimensional grid, which is not addressed by this profile. The attribute scanDirection contain a list of signed attribute names; scanning starts in a direction parallel to the first axis listed, and moves from row to row in the direction parallel to the next axis listed.
Linear scanning cannot be used if data has been aggregated as a result of data compaction. In that case the value of the sequencingRule shall be Morton. Morton ordering is discussed in detail in Annex C.
startSequence
The attribute startSequence : CV_GridCoordinate shall identify the grid point to be associated with the first record in the values sequence. The choice of a valid point for the start sequence is determined by the type and scanDirection attributes of CV_SequencingRule.
values
The values attribute of the ESM_GridValues class shall be a sequence of Records each containing one or more elevation values to be assigned to a single grid point. The Record shall conform to the RecordType specified by the rangeType attribute of the ESM_GridCoverage class with which the ESM_Grid class is associated. Only elevation values are required when the sequence rule is of type linear.
Note that the coverage may describe more than one surface, in which case the Record contains more than one elevation value for each grid point. Each surface is evaluated independently. Aggregations of points resulting from data compaction shall be the same for all surfaces described by a coverage.
Variable Cell Size Grids
The class IF_RiemannGriddedData from ISO 19129 is a subclass of the class IF_GridCoverage that implements the class CV_ContinuousQuadrilateralGridCoverage from ISO 19123. The Riemann class defines a variable cell size grid where adjacent cells that have the same attribute values are aggregated along the traversal order. This grid, known as a quad tree in 2 dimensions, is of particular use for large volumes of sensor data where many adjacent cells have similar values and can be aggregated into larger cells.
The Riemann coverage template differs from the continuous quadrilateral grid coverage template in that the traversal order for the Riemann grid is Morton and the aggregation rule for adjacent cells is applied. It is necessary to describe the minimum grid cell dimensionality and axis order using the attributes dimension and axisNames inherited by CV_GridValuesMatrix from CV_Grid.
Variable sized cells are actually aggregations of small equally sized cells as defined by CV_GridValueCell. The nature of the Morton order means that only the size of each cell need be stored along with the cell value. The position of each cell is uniquely defined by the cell size and the traversal order. In a simple regular grid the location of each cell is uniquely defined by the Row, Column traversal order. In a Riemann grid the location of each cell is defined by the cell size (aggregation level) and the Morton order.
In continuous coverages, a coverage function returns a value for every point in the area covered based on an interpolation function. The Grid Value Matrix is a set of values which drives the interpolation function. In this case the value matrix is a subclass of CV_GridValuesMatrix that includes the additional parameter defining the cell size as a level of aggregation. That is, 0 represents the base minimum cell size, and 1 represents the aggregation of one level of adjacent neighbors, and 2 represents the aggregation of one more level of adjacent neighboring cells.
ESM TIN Coverage
Introduction
A TIN covers an area with a unique set of non-overlapping triangles where each triangle is formed by three points. The geometry for a TIN is described in ISO 19107 and TIN coverages are described in ISO 19123. Most of the points in a well-constructed TIN fall on the inflection points (ridges, drains, summits and pits) of the surface it represents, so it may represent the surface more accurately than a grid of the same point density. TIN coverages are particularly useful for representing elevation in some applications. It is easier to calculate an intersection with a coverage surface when it is represented as a TIN. Attributes can be applied to each triangular face, and it is easy, but computationally intensive, to process the faces geometrically, in order to calculate contour lines. The major advantage of a TIN is in those applications where it is desirable to calculate the intersection of a path with the elevation surface. An example TIN showing variable-size TIN triangles and the TIN vertices is shown in Figure 7. There are two common methods of storing TIN data: as triangles with references to their vertices, or as points with references to their neighbouring points.
Figure 7 - Example TIN Triangles
Elevation TIN Coverage Model
A TIN elevation coverage is a subclass of CV_ContinousCoverage (ISO 19123) characterized by a GM_TIN (ISO 19107). The attribute values in the value record for each CV_GeometryValuePair of a CV_TINcoverage represent elevation values. Any additional attributes related to a TIN triangle may be described as attributes of the component triangles. The class ESM_TINCoverage is illustrated in Figure 8.
Figure 8 - ESM TIN Coverage
ESM_TINCoverage Class
The class ESM_TINCoverage is a realization of the Type CV_TINCoverage from ISO 19123. CV_TINCoverage is an aggregation of CV_ValueTriangle, which uses GM_Triangle (ISO 19107) as its geometry. Each of the vertices of the GM_Triangle represents a specific elevation.
interpolationType
The attribute interpolationType specifies the interpolation method recommended for the evaluation of the ESM_TINCoverage. The value is taken from the code list CV_InterpolationMethod specified in ISO 19123. For TIN coverages, the default value is barycentric.
The barycentric position S within a value triangle composed of the CV_PointValuePairs (P1, V1), (P2, V2), and (P3, V3), is (i, j, k), where S = iP1 + jP2 + kP3 and the interpolated attribute value at S is V = iV1 + jV2 +kV3.
geometry
The attribute geometry contains the network of triangles that form the basis of the TIN. The class GM_Triangle is used to construct GM_TIN (ISO 19107). GM_TIN has a controlPoint attribute which contains a set of GM_Positions (ISO 19107), and GM_Positions are unions of either DirectPositions or references to GM_Points from which DirectPositions can be derived. The triangles within a TIN lie on a 2-dimensional manifold with the X,Y coordinates of the points at the vertices of the triangles representing the direct position on the manifold and the attribute value representing the elevation above the reference surface (e.g. the WGS84 ellipsoid).
ESM Point Coverage
ESM Point Coverage Model
An ESM point coverage is a type of CV_DiscretePointCoverage from ISO 19123. The attribute values in the value record for each CV_GeometryValuePair represent elevation values.
The class ESM_PointCoverage (Figure 9) represents a set of elevation values assigned to a set of arbitrary X,Y points. Each point is identified by a horizontal coordinate geometry pair (X,Y) and assigned one or more elevation values as attribute values. The point set does not necessarily have any systematic organization, although the arrangement of the points may depend upon the characteristics of the sensor or process by which they were generated.
Figure 9 ESM Point Coverage
ESM Point Coverage Class
The class ESM_PointCoverage is a subclass of ESM_Coverage and a realization of the Type CV_DiscretePointCoverage specified in ISO 19123. It is an aggregation of points, each of which is associated with one or more elevation values carried as attributes. It implements the attributes and associations inherited from ESM_Coverage as well as those specified for CV_DiscretePointCoverage. A point coverage supports the description of multiple surfaces using 2-dimensional points with elevation values described as attributes in a record. This is different from a point set which is a set of 3-dimensional points each of which relates to only one surface.
element
The role name element identifies the set of ESM_Points contained in the ESM_PointCoverage.
ESM Point Class
The class ESM_Point is a realization of the Type CV_PointValuePair specified in ISO 19123. It represents a point that has a Record of one or more elevation values associated with it. The location of a point is specified by the attribute geometry which contains an instance of GM_Point as specified in ISO 19107. The position of the GM_Point shall be constrained to 2 dimensions and specified with reference to WGS84 ( REF _Ref142802654 \r \h \* MERGEFORMAT 8.2). A Record may contain one or more elevation values where each value corresponds to a different surface.
Point Sets
Point sets consist of point features that are referenced to a 3-dimensional coordinate reference system. In other words, a member of an elevation point set differs from an ESM_Point in that its elevation is carried as a coordinate rather than an attribute. A point set is therefore not a coverage, but is only the spatial domain of a coverage. Point set data is generated by certain types of sensors. A point cloud collected by a LiDAR sensor is an example of a point set. Each point in a point set has only one elevation value and represents only one elevation surface type. Through processing it is possible to convert a point set into a point coverage.
Metadata
Introduction
Associated with each dataset (either an ESM_Coverage or an ESM_Point set) and with each ESM_Collection is metadata. The information provided by the metadata allows and enhances data discoverability, access and transfer. It can also allow a determination of the datas fitness for use in a particular application. Metadata is organized in various ways according to the exchange format that carries the information. At one level, all of the information within the dataset, other than the set of value objects, may be considered metadata. Thus, an attribute in one exchange format may appear as metadata in another. Additionally, implementation of specific metadata elements could vary based on the interpretation of the metadata producers. This profile specifies that standardization of the metadata vocabulary and entity relationships will be achieved through conformance with the DGIWG Metadata Foundation (DMF) and ISO 19115 metadata schema. Annex E of this profile includes a DMF-compliant data dictionary for minimum required ESM metadata. ISO rules for encoding the schemas in XML are also required by this profile. The XML schemas will enhance interoperability by providing a common specification for describing, validating and exchanging metadata associated with elevation datasets.
Metadata Hierarchy Levels
In practice, metadata may be associated with any class or subset of data, including individual points or cells, a grouping of data within a dataset, a single fundamental dataset, or an aggregation of datasets. The description of metadata is hierarchical, so that any metadata element at a higher level applies at a lower level, unless superseded by more detailed metadata at the lower level. For example, an individual hydrographic sounding within a bathymetric depth coverage might carry information about the accuracy of the individual sounding, and this would supersede accuracy metadata described for the region of the dataset that includes the sounding.
Data Interchange
ISO 19115 defines a dataset (DS_Dataset) as an identifiable collection of data. A dataset can be represented in an exchange format or stored on a storage media. It must have one or more related metadata entity sets (MD_Metadata), which may optionally relate to aggregations of datasets (DS_Aggregate).
However, a dataset cannot be defined as a physical entity of exchange, but rather as a logical entity that can be identified by its associated metadata. Therefore, metadata based transfers of geospatial information require the 19115 model to be extended (Figure 10). To support interchange by transfer, two new concepts are introduced by ISO 19139; the transfer dataset (MX_Dataset) and the transfer aggregate (MX_Aggregate). In the context of the transfer, the dataset data is organized into data files (MX_DataFile). The ESM_Collection (6.4) is a realization of the transfer aggregate. Both transfer datasets and aggregates may reference support files (MX_SupportFile) which contain resources needed to exploit the data or complementary information. Examples of support files include feature and portrayal catalogues, codelists, and documents defining units of measure or coordinate reference systems.
Figure 10 General Interchange Organization
In an actual (physical) transfer, the aggregation of datasets follows constraints (e.g. media capacity) and requirements which outweigh this conceptual design, but the initial nature of the aggregation can be expressed through the hierarchyLevel attribute of MD_Metadata using the codelist MD_ScopeCode. The concept of a transmittal is introduced in ISO 19129 to identify the information that is physically exchanged. A transmittal may be a dataset, a part of a dataset, or several datasets, depending on the encoding format and the exchange media. A transmittal on a physical media such as a DVD may carry a number of datasets, whereas a transmittal over a low bandwidth telecommunications line may carry only a small part of a dataset. Transmittal metadata describes the transfer data file (MX_DataFile). This metadata is integral to the transmittal and may be changed by the exchange mechanism to other exchange metadata as required for the routing and delivery of the transmittal. A common exchange mechanism would be to carry a whole dataset on one physical media such as a CD-ROM. Transmittal metadata is dependent upon the mechanism used for exchange, and may differ from one exchange media or encoding format to another. An example of transmittal metadata would be counts of the number of data bytes in a unit of exchange. It is recommended that the transmittal metadata include the resource format (MD_Format) to describe the exchange format of the corresponding value data.
Metadata Content Requirements
The specification of minimum required metadata elements in Annex E complies with the DGIWG Metadata Foundation (DMF) and schema defined in ISO 19115. It defines the minimum set required to serve the full range of metadata applications, including the enablement of data discovery, access, transfer and use, and the determination of the datas fitness for use. In the following subsections, metadata requirements that represent additional constraints or recommendations beyond those provided by the DMF and ISO standards are described.
Intended Use
Communities of practice have unique requirements with respect to density, accuracy and other characteristics of the data, and this profile does not prohibit data producers or users from representing any data for any specific use. However, in order to prevent inappropriate use of elevation data based on characteristics such as spatial resolution and data quality, this profile requires that producers include the intended use of the data as a metadata element. The MD_Usage class of metadata is required in the ESM metadata specification (Annex E).
Surface Type
Surface type is an important attribute of the data but is difficult to describe. There are two relevant concepts: material surface and observed surface. A material surface is a surface along which two bodies of different types of material are in contact. An observed surface is a surface detected by a remote sensor. The two do not always correspond. This profile requires the documentation of surface type definitions in a feature catalogue. The surface type(s) defined by the elevation values shall be declared in the metadata, using the Keywords element defined in Table E.1. Including the surface type as a searchable keyword will make the elevation dataset discoverable by surface type, which may be necessary to support the intended use of the data.
A material surface may be detected by a remote sensor because the materials on opposite sides of the surface react differently to incident energy or emit energy differently. In the simple case, energy is reflected or emitted directly from the surface, so the observed surface corresponds closely to the material surface. In other cases, incident energy penetrates a material surface but is scattered back to a sensor before reaching the next material surface. If the depth of penetration is less than the resolution of the sensor, the sensor will average the positions from which energy is returned to generate an apparent surface below or behind the actual material surface. This is especially true for LiDAR, radar, sonar, and seismic sensors.
For most practical applications, it is the material surfaces that are of interest. These include:
Bare earth
Vegetation canopy
Bedrock
Water (open water and/or subterranean water table)
Sea floor (and bottom surfaces of other water bodies)
Ice
Built-up surfaces (including pavements)
When it is not clear that an observed surface corresponds to a material surface, the surface should be identified by the wavelength or frequency of the sensed radiation.
Estimated Values
No material surface is truly continuous. However, it is often possible to derive heights of one surface type from those of another. For example, heights for a "bare earth" surface can be estimated for points occupied by buildings either by subtracting building heights or by interpolating between bare earth points outside the building footprint. When estimated values are included in the dataset, information about the method used for the estimation shall be included in a product specification and in the metadata using the Method used to estimate values metadata element (Table E.1)
Accuracy
ISO 19138 provides the data producer with guidance in choosing appropriate data quality measures for reporting, and assists the user in the evaluation of the usefulness of a dataset by standardizing the components and structures of data quality measures. The final choice must be based upon the type of data, the production process and the resources available. The resulting values and the method employed should be declared so that producers and users can understand the assessment and its validity. The stated accuracy requirement of a finished elevation product will be dependent on the intended use of the data. NATO STANAG 2215 Evaluation of Land Maps, Aeronautical Charts and Digital topographic Data, Edition 6, specifies Circular and Linear Map Accuracy Standard (CMAS and LMAS) requirements, but does not address high resolution datasets. This standardized profile addresses all spatial resolution levels but only requires that horizontal/vertical accuracy values be expressed at a confidence level of at least 90 percent (circular/linear error at > 90 percent probability). In general, applications that require high density also require high relative accuracy. As accuracy requirements become more stringent, assigning a single value of horizontal and vertical error for an entire dataset becomes an unsatisfactory solution. Therefore, Annex F of this profile describes the metadata contents that are required to permits rigorous, high fidelity error estimates to be computed on a post-by-post basis for a grid coverage. For high-resolution datasets ( REF _Ref388882738 \h Table ), the data accuracy information shall be included in the metadata and shall include error propagation estimates. Reporting of this information may require the inclusion of quality coverages in addition to the elevation value coverage. In this case, a reference to the accuracy coverage shall be made in the metadata (QE_CoverageResult class from ISO 19115-2). If a dataset is subdivided into regions according to the quality of the elevation measurements, the geographic extents to which the accuracy values apply must be specified. General metadata requirements for accuracy reporting of any elevation dataset are included in Annex E.
Void and Suspect Areas
Identification of void areas is a requirement that only applies to grids since TINS, point coverages and point sets have no need for fill or pad values. The gridded data formats that are used to carry elevation data generally have some provision to declare a value for void areas. Some data producers assign large negative values to postings for void areas to retain the array alignment of raster data. Since this profile supports bathymetric data as well as land heights, using a negative value for void points in the grid cannot be recommended for all elevation datasets. Due care must be taken to avoid confusion with actual data values. The value shall be declared in the metadata, either by using the rangeElementDescription role from 19115-2 or by defining a void polygon using the extentTypeCode attribute of EX_GeographicExtents (see Table E.1). Completeness metadata is also required per Annex D (DQ_DataQuality). Suspect areas have associated elevation values that are obviously outside of the logical range for the surface described. Suspect areas can be adequately addressed using elements of the DQ_DataQuality class.
Coordinate Reference Systems
ISO 19115, the DMF, and this profile require the use of an identifier for the reference system. The allowed horizontal reference systems are World Geodetic System 1984 (hereafter WGS84) and UTM or UPS projection on WGS84. The allowed vertical reference systems are the WGS84 Ellipsoid, WGS84 Geoid, or a hydrographic datum. The Earth Gravity Model (EGM) version shall be specified when the WGS84 geoid is the vertical reference system. This may be accomplished through the use of the Temporal Reference System element listed in Table E.1. Section 8 provides guidance on the implementation of ESM allowed reference systems.
Units of measure
The units of measure shall be implied by the specified coordinate reference system. User-defined reference systems are not allowed by this profile, and therefore a specific declaration of the horizontal or vertical units of measure is not required. The unit of measure for the UTM/UPS system is meters. The unit of measure for the WGS84 (geographic) horizontal reference system shall be expressed as decimal degrees. The vertical unit of measure for WGS84 is also meters, and meters shall be implied as the unit of measure when hydrographic datums are used.
Processing history
Information describing the processing that has been applied to the data shall be documented using the lineage metadata elements. This shall include information about the source, the method of data capture, and any information on the transformation, conversion, or resampling that has been applied to the data.
Data Maintenance
Information describing the approach, currency and history of maintenance is to be documented in the metadata. Maintenance of datasets is not mandatory, but it shall be clear from the metadata whether a dataset is maintained or is static.
Dataset Identifiers
A system for assigning permanent unique identifiers to each and every dataset, data subset, and metadata file is essential for the successful application of this standardized profile. This can be accomplished by using a concatenation of identifiers in which each identifier is unique within a specified scope. The largest scope specified by this profile is the organization that produces, maintains, or distributes elevation surface data. Within the scope of an organization, the following rules shall be applied.
A persistent elevation collection shall be assigned an identifier that is unique within the scope of the organization that maintains the collection. A transient collection, such as a transmittal, need not be assigned a permanent identifier.
A fundamental dataset shall be assigned an identifier that is unique within the scope of the organization that produced it.
A tile or sub-group within a fundamental dataset shall be assigned an identifier that is unique within the scope of that fundamental dataset.
A metadata file shall be assigned an identifier that is unique within the scope of the organization that produced it
Reference Systems
Types of referencing
Position relative to the earth is described in terms of a coordinate reference system. Three-dimensional geospatial data positions are usually referenced to a compound coordinate reference system (ISO 19111) composed of a 2-dimensional horizontal reference system ( REF _Ref141610886 \r \h \* MERGEFORMAT 8.2) and a one-dimensional vertical reference system ( REF _Ref141610936 \r \h \* MERGEFORMAT 8.3). For high-resolution elevation data, the realization epoch (date of observation recorded as temporal extents) is also required, to account for the movement of positions on the Earth over time.
Horizontal reference systems
Introduction
Horizontal positions of elevation points shall be directly or indirectly referenced to the World Geodetic System 1984 (WGS84) [DMA TR 8350.2]. Horizontal referencing of points in a grid is a special case ( REF _Ref146442374 \r \h \* MERGEFORMAT 8.2.4).
Direct referencing
For direct referencing, horizontal positions of points included in TIN coverages, point coverages, and point sets shall be expressed as WGS84 latitude and longitude.
Indirect referencing
For indirect referencing, horizontal positions of points included in TIN coverages, point coverages, and point sets shall be expressed as Northing and Easting in the Universal Transverse Mercator (UTM) or Universal Polar Stereographic (UPS) Grid Systems [NIMA TM 8358.2] based on the WGS84 datum and ellipsoid. The unit of measure for both UTM and UPS is meters.
Grid referencing
Introduction
The points in a grid are referenced to an internal grid coordinate system. The internal coordinate reference system for a rectified grid is specified by an origin (6.7.5) and two offset vectors (6.7.6) that are specified in terms of an external coordinate reference system. This standard permits referencing of grids to two external coordinate reference systems. A grid coordinate system may be directly referenced to WGS84 coordinates, or it may be referenced to a UTM Grid based on the WGS84 datum.
NOTE A rectified grid is specified with respect to a particular external coordinate reference system. Representation in any other coordinate reference system will distort the shape of a cell and the parallelism of its sides.
Grid coordinates referenced to WGS84 coordinates
The position of the origin of a grid referenced to WGS84 coordinates shall be specified as WGS84 latitude and longitude. The offset vectors that describe the grid shall be parallel to the meridians and parallels of the WGS84 coordinate system, and their ordinates shall be specified in terms of arc seconds angular measure.
Grid coordinates referenced to the UTM Grid
The position of the origin of a grid referenced to the UTM Grid System shall be specified as UTM Northing and Easting in meters. Ordinates of the offset vectors that describe the grid shall be expressed in meters. The reference origin for UTM datasets will be the origin of the UTM zone in which the data is located. UTM zone origins are specified by the intersection of the UTM zone central meridian with the equator. This intersection is assigned the UTM coordinates 500000.0 E, 0.0 N for zones in the northern hemisphere and coordinates 500000.0 E, 10000000.0 N for zones in the southern hemisphere. If the point spacing of a given d a t a s e t i s s p e c i f i e d a s { "E , "N } , t h e n p o i n t s i n t h e N o r t h e r n h e m i s p h e r e w i l l b e d e f i n e d a t { 5 0 0 0 0 0 i * "E , 0 + j * "N } . T h e v a l u e s i a n d j a r e i n t e g e r v a l u e s o f p o i n t s i n t h e E a s t i n g a n d N o r t h i n g d i r e c t i o n ( r e s p e c t i v e l y ) , + i * "E s i g n i f i e s a n e a s t e r l y d i r e c t i o n f r o m t h e c e n t r a l m e r i d i a n , - i * "E s i g n i f i e s a w e s t e r l y d i r e c t i o n f r o m t h e c e n t r a l m e r i d i a n , a n d + j * "N s i g n i f i e s a n o r t h e r l y d i r e c t i o n f r o m t h e e q u a t o r . I n a s i m i l a r f a s h i o n , p o i n t s i n t h e S o u t h e r n h e m i s p h e r e a r e s p e c i f i e d b y { 5 0 0 0 0 0 i * "E , 1 0 0 0 0 0 0 0 - j * "N } , w h e r e i a n d j a r e i n t e g e r v a l u e s o f p o i n t s i n t h e E a s t i n g a n d N o r t h i n g d i r e c t i o n ( r e s p e c t i v e l y ) , + i * "E s i g n i f i e s a n e a s t e r l y d i r e c t i o n f r o m t h e c e n t r a l m e r i d i a n , - i * "E s i g n i f i e s a w e s t e r l y d i r e c t i o n f r o m o f t h e c e n t r a l m e r i d i a n , a n d - j * "N s i g n i f i e s a s o utherly direction from the equator [NOTE: for gridded data, the points are stored in row/column order]. Adhering to this system will assure that coincident points are maintained across the various levels of horizontal resolution within a zone. This will allow for direct comparison between datasets and direct decimation of higher-resolution data to lower resolutions. Figure 11 shows an example of UTM Point Locations in Northern Hemisphere.
Figure 11 - Example of UTM Point Location In Northern Hemisphere
(Note that the various symbols represent different resolution levels, but illustrate collocated points)
Vertical reference systems
A vertical reference system consists of a surface identified as a datum from which heights are measured and an axis normal to the surface through the point for which the height is stated. The WGS84 ellipsoid, which is the fundamental datum used by the Global Positioning System, is preferred as the common datum for all elevation surface data. However, reference to a geoid is often more useful for terrestrial applications. Since water depths vary with the tides, bathymetric data is normally referenced to a datum defined in terms of tide state.
This profile permits the use of any of the following vertical datums:
The WGS84 ellipsoid [DMA TR 8350.2]
The geoid defined by the WGS84 Earth Gravity Field Model (EGM). The specific model (e.g. EGM2008) shall be specified in the metadata.
A sounding datum or hydrographic datum, which is a vertical datum based on a selected tide level related to Mean Sea Level (MSL). The specific tidal datum used depends on the type of tide in the area or on the number and magnitude of high and low tides in one tidal cycle.
In this standard the default is the WGS84 ellipsoid, and when used, the hydrographic datum must be explicitly referenced in the metadata. User-defined vertical datums are prohibited by this profile.
Spatial Resolution
Spatial resolution is a significant attribute in determining the appropriate usage of an elevation dataset, and standardization of the resolutions within a product line will therefore enhance discoverability. A product specification for gridded data will typically specify the post spacing for the product levels. Elevation datasets with horizontal spatial resolution of 12 meters (.4 arc seconds of longitude at the equator) or higher are defined as high-resolution data by this profile. Five levels of horizontal point spacing are suggested here for high-resolution, projected data ( REF _Ref388882738 \h Table ). The high-resolution levels are given in terms of nominal metric spacings for gridded data referenced to UTM coordinates, as this referencing is recommended for high-resolution data (see Section 8.2.4.3).
Table 2 - Elevation Grid Resolution Levels for Projected Data (Informative)
LevelHorizontal Grid
spatial resolutionHorizontal Units18meters24meters32meters41meters50.50metersPoint spacing has always been the measure for the spatial resolution of regularly gridded elevation data, and grids with spacings within 25% of a nominal value for spacing are considered to be at the same level of resolution. While this profile does not require the use of specific levels of horizontal resolution, it is recommended that gridded datasets have a spacing that is consistent with the datasets vertical accuracy, and also with the type of terrain being modeled. For flat and undulating terrain, a spacing that is between 3 and 20 times the vertical root mean square error (RSMEv) is recommended. For complex terrain, a spacing between 3 and 10 times RSMEv is appropriate. Standard deviation based on terrain relief is also useful in determining an appropriate post spacing.
Grids referenced to WGS84 geodetic coordinates (8.2.4.2) are a special case. Because the grid is not projected to a 2D surface, these spacings must be specified in terms of angular measure: arc seconds of latitude and longitude. The linear measure of a second of longitude varies with the latitude, and five latitudinal bands are defined here ( REF _Ref388883078 \h Table ) so that the linear spacing between points is roughly equivalent at all latitudes. NATO STANAG 3809 (DTED) defines standard grid spacings at two levels of resolution.This standard extends the definition of standard spacings to cover 2 additional levels for unprojected data. Note that Levels 3 and 4 fall into the ESM categorization of high-resolution data. Grid spacings specified in terms of latitude and longitude are generally not recommended for high-resolution data, but they are appropriate for grids that extend across zone boundaries of the UTM Grid.
Table 3 - Elevation Grid Resolution Levels for Data Referenced to WGS84 Geographic Coordinates (Informative)
BandLatitude (N/S)Level 1
Lat x LonLevel 2
Lat x LonLevel 3
Lat x LonLevel 4
Lat x Lon10 - 503 x 31 x 10.4 x 0.40.1 x 0.1250 - 703 x 61 x 20.4 x 0.80.1 x 0.2370 - 753 x 91 x 30.4 x 1.20.1 x 0.3475 - 803 x 121 x 40.4 x 1.60.1 x 0.4580 - 903 x 181 x 60.4 x 2.40.1 x 0.6
Again these levels are merely suggestions for storage and usage at standardized resolution levels. An elevation database service can be designed to output datasets at any user-specified spatial resolution or projection. For example, a user may want elevation data for a geographic area at multiple resolutions and referenced to the ARC projection system so that the data will align with coinciding raster maps of various scales. DGIWG follows NATO policy for categorization of digital geospatial data by equivalence to paper map scales, as provided in REF _Ref388883206 \h Table 4.
Table 4 - NATO Resolution Levels for Geospatial Information
LevelPaper Map Equivalent Scales (S)Imagery Resolution (I)Matrix Resolution (M)0S < 1:1,000,000Not usedM > 100 meters (m)11:1,000,000 < S < 1:250,000 I e" 1 0 m e t e r s ( m ) 1 0 0 m e" M > 3 0 m 2 1 : 2 5 0 , 0 0 0 <