Open Geospatial Consortium Inc.
Date: 2009-01-15
Reference number of this OGC® document: 07-092r3
Version: 1.3®

Category: OGC Best Practices
Editor: Arliss Whiteside

Definition identifier URNs in OGC namespace

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.
To obtain additional rights of use, visit http://www.opengeospatial.org/legal/.

This document defines an OGC Best Practices on a particular technology orapproach related to an OGC standard. This document is not an OGC Standard andmay not be referred to as an OGC Standard. It is subject to change without notice.
However, this document is an official position of the OGC membership on thisparticular technology topic.

Document type:
Document subtype:
Document stage:
Document language:

OGC® Best Practices
Best Practices Paper version 1.3
EnglishOGC 07-092r3

Contents

Pagei.
Preface.................................................................................................................... iv
ii.
Document contributor contact points ..................................................................... iv
iii.
Revision history .......................................................................................................v
iv.
Changes to the OGC Abstract Specification ............................................................v
v.
Future work ..............................................................................................................v
Foreword ............................................................................................................................ vi
Introduction ........................................................................................................................ vi
1
Scope ........................................................................................................................1
2
Conformance ............................................................................................................1
3
Normative references ...............................................................................................1
4
Terms and definitions ..............................................................................................3
5
Conventions .............................................................................................................5
5.1
Symbols (and abbreviated terms) ..........................................................................5
5.2
Document terms and definitions ............................................................................5
6
Background ..............................................................................................................6
6.1
Definition identifiers .............................................................................................6
6.2
Use for Coordinate Reference Systems .................................................................6
6.3
Relationships to other identification schemes .......................................................7
6.3.1 URN and URL ....................................................................................................7
6.3.2 URN and schema component designators...........................................................8
7
OGC URN scheme for definitions ...........................................................................9
7.1
OGC URN scheme ................................................................................................9
7.2
URNs for single objects.........................................................................................9
7.3
URN extensions for OGC ....................................................................................13
7.4
URNs for not-completely-specified objects ........................................................14
7.5
URNs for combined objects ................................................................................15
7.5.1 Overview ...........................................................................................................15
7.5.2 URN combined references for compound coordinate reference systems .........16
7.5.3 URN combined references for concatenated operations ...................................16
7.5.4 URN combined references for projected or derived CRSs ...............................17
7.5.5 URN combined references for datum and coordinate system...........................17
8
URN values for definitions and concepts in ogc namespace .................................17
8.1
Introduction .........................................................................................................17
8.2
CRS definitions ...................................................................................................18
8.3
CRS code list values definitions ..........................................................................18
8.4
Unit-of-measure (uom) definitions ......................................................................21
8.5
Data type definitions............................................................................................21ii

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OGC 07-092r3

Annex A (normative) GML dictionaries of OGC definitions ...........................................24
A.1
Introduction .........................................................................................................24
A.2
Definitions of derivedCRSType values ...............................................................24
A.3
Definitions of verticalDatumType values ...........................................................26
A.4
Definitions of pixelInCell values.........................................................................27
A.5
Definitions of rangeMeaning values ...................................................................27
A.6
Definitions of axisDirection values .....................................................................28
A.7
Definitions of units-of-measure ...........................................................................34
A.8
Definitions of data types ......................................................................................35
Bibliography ......................................................................................................................40

TablesPage

Table 1 — “authority” values for definitions in OGC URN namespace ....................................... 11
Table 2 — “objectType” values for definitions in OGC URN namespace ................................... 12
Table 3 — URNs for CRSs defined by OGC ................................................................................ 18
Table 4 — URNs for derivedCRSType values ............................................................................. 19
Table 5 — URNs for verticalDatumType values .......................................................................... 19
Table 6 — URNs for pixelInCell values ....................................................................................... 19
Table 7 — URNs for rangeMeaning values .................................................................................. 19
Table 8 — URNs for axisDirection values.................................................................................... 20
Table 9 — URNs for units-of-measure ......................................................................................... 21
Table 10 — URNs for data types .................................................................................................. 22

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

iii

OGC 07-092r3

i.

PrefaceThis version 1.2 includes Corrigendum 2 as specified in [OGC 06-152r1].
This Best Practices Paper specifies Universal Resource Names (URNs) in the “ogc” URN
namespace to be used for identifying definitions. This document specifies the formats
used by these URNs, plus a set of specific URNs for specific definitions. These
definitions should be used wherever applicable by implementations of various OGC
Implementation Standards, including GML, WMS, WFS, and WCS.
In this version of the document several modifications are made to reflect the fact that the
EPSG dataset is now available in a data registry (www.epsg-registry.org). Furthermore
some modifications reflect a change in Topic 2 - Spatial Referencing by Coordinates.
This document does not require or encourage OGC standards to use only URNs definedin the "ogc" URN namespace. In addition, it does not encourage use of URNs when
URLs are appropriate. Furthermore, other OGC documents do and can specify more
URNs in the "ogc" URN namespace.
However, OGC standards should specify that all URI values used with that standard havewell-specified formats and meanings, preferably electronically accessible meanings. If
well-specified URI values are not available for an OGC standard need, specification of
new URNs in the "ogc" URN namespace should be considered (in that standard or
elsewhere). If new URNs are being specified in another URN namespace for use with
OGC standards, it would be useful if the same URN structure is used as is used by the
OGC.
Suggested additions, improvements, and comments on this Best Practice are welcomeand encouraged. Such suggestions may be submitted to the editor by email message.
Extensive and/or multiple changes can be suggested by making changes in an edited copyof this document. If you choose to submit suggested changes by editing this document,
please make your suggested changes with change tracking on.

ii.

Document contributor contact points

All questions regarding this document should be directed to the editor or the contributors:
Name
Arliss Whiteside
John Evans
Keith Pomakis
Simon CoxRoel Nicolaiiv

Organization
BAE Systems E&IS
NASA / GST, Inc.
CubeWerx, Inc.
CSIRO Exploration and Mining
Shell International E and P

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OGC 07-092r3

iii.

Revision history
Date

Release

2004-12-17 0.0.0
2005-01-07 0.0.0
2005-01-26 1.0.0

2006-02-13 1.0.1
2006-07-04 1.0.2
2006-07-24 1.1.0
2007-07-27 1.1.2
2007-09-28 1.1.2
2008-08-22 1.2

2008-10-06 1.3
2009-09-09 1.3

iv.

EditorPrimary clauses
modifiedAll
Initial version

ArlissWhiteside
Arliss7.1, 7.2
Whiteside
ArlissCover, i, 7.1, 7.2
Whiteside
ArlissWhiteside
Simon
Cox
ArlissWhiteside
ArlissWhiteside
ArlissWhiteside
Roel
Nicolai

Description

Cover, i, 7.1,
7.5, Av, 6.1, 6.3, 7.1

Adds information on referencing EPSG coordinate
axis objects
Removed information on referencing EPSG
coordinate axis objects, edited as approved
Recommendation Paper
Added additional allowed “authority” and“objectType” values, plus URNs for data types
Add to future work, TBD

All

Final editing

Cover, iii

Make changes described in Corrigendum 2 [OGC
06-152r1]
Cleanup following approval

7.2 , 8.3, AnnexA

Roel
7.2 , 8.3, Annex
Nicolai
A
Carl Reed Various

Extension objectTypes by Area; removal of
conditional mandatory nature of ‘version’ in URN;
update with changes to Topic 2
Includes final edits of version 1.2; extension of listof objectTypes rejected.
Minor edits in preparation for publication as BP

Changes to the OGC Abstract Specification

The OGC® Abstract Specification does not require changes to accommodate the technicalcontents of this document.

v.

Future work

Improvements in this document are desirable to:a) Add more and complete existing examples in Clause 7b) Specify additional URNs in Clause 8c) Specify meanings of additional URNs in Annex Ad) Replace static list of Authorities with dynamic registry (hosted by OGC Network)e) Replace the static list of Object Types with dynamic registryf)

Point to standard resolution service for OGC URNs

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OGC 07-092r3

Foreword
This document includes one normative annex: Annex A.
Attention is drawn to the possibility that some of the elements of this document may be
the subject of patent rights. The Open Geospatial Consortium Inc. shall not be held
responsible for identifying any or all such patent rights.
Recipients of this document are requested to submit, with their comments, notification of
any relevant patent claims or other intellectual property rights of which they may beaware that might be infringed by any implementation of the standard set forth in thisdocument, and to provide supporting documentation.

Introduction
This document specifies Universal Resource Names (URNs) in the “ogc” URN
namespace to be used for identifying definitions. These definitions include definitions of
Coordinate Reference Systems (CRSs) and related objects, as specified in OGC Abstract
Specification Topic 2: Spatial referencing by coordinates, plus several other resource
types for which standard identifiers are useful in OGC Web Services. This document
specifies the formats used by these URNs, including formats that can reference
definitions recorded in the EPSG database and by other authorities. This document also
specifies URNs for some specific definitions for which OGC is the custodian.

vi

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OGC® Best Practices

OGC 07-092r3

Definition identifier URNs in OGC namespace

1

Scope

This document specifies Universal Resource Names (URNs) in the “ogc” URN
namespace to be used for identifying definitions. These definitions include definitions of
Coordinate Reference Systems (CRSs) and related objects, as specified in OGC Abstract
Specification Topic 2: Spatial referencing by coordinates. This document specifies theformats used by these URNs, including formats that can reference any definition recordedin the EPSG database. This document also specifies URNs for some specific definitions.
This document specifies URN formats for several uses, currently including referencing
definitions of:a) Single objectsb) Not-completely-specified objectsc) Combined objects
Most XML attributes and elements with the anyURI data type that reference definitions,in all approved and draft OGC Implementation Standards, can use a URN value in the“ogc” URN namespace. Such a URN shall be used when a URL cannot be used toelectronically access that definition, by all clients and servers that may need to reference
that definition.
The “ogc” definition URNs specified here should be used wherever applicable byimplementations of all approved and draft OGC Implementation Standards, including
GML, WMS, WFS, and WCS. Additional definition URNs in the “ogc” URN namespace
are and will be specified in other OGC documents.
2

Conformance

Conformance with this Best Practice shall be checked using all the relevant tests
specified in each separate specification that normatively references this Best Practice, andspecifically references the applicable parts of this Best Practice.
3

Normative references

The following normative documents contain provisions which, through reference in thistext, constitute provisions of this document. For dated references, subsequent

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

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OGC 07-092r3

amendments to, or revisions of, any of these publications do not apply. For undated
references, the latest edition of the normative document referred to applies.
European Petroleum Survey Group database: EPSG Geodetic Parameter Dataset,available through http://www.epsg.org/ and accessible on-line through www.epsgregistry.org
IETF RFC 2141 (May 1997), URN Syntax, R. Moats<http://www.ietf.org/rfc/rfc2141.txt>
IETF RFC 2396 (August 1998), Uniform Resource Identifiers (URI): Generic Syntax,
Berners-Lee, T., Fielding, N., and Masinter, L., eds.,<http://www.ietf.org/rfc/rfc2396.txt>
ISO/IEC 18025:2005, Information technology — Computer graphics and image
processing — Environmental Data Coding Specification (EDCS)
ISO 31:1992, Quantities and Units. (13 Parts, with revisions 1998)
ISO 1000:1998, The International System of Units (SI), 7th edition
ISO 19109:2004. Geographic information - Rules for application schema
OGC 03-105r1, OpenGIS Geography Markup Language (GML) Implementation
Standard, Version 3.1.0
OGC 06-166, A URN namespace for the Open Geospatial Consortium (OGC), draft
OGC 06-042, Geographic information — Web Map Service interface, v1.3.0
OGC 04-092r4, OpenGIS Geography Markup Language (GML) Implementation
Standard Schemas, Version 3.1.1
OGC 06-121r3, OGC Web Services Common Standard, Version 1.1.0
OGC 05-020r5, Technical Committee Policies and Procedures
OGC 05-087r2, Observations and Measurements
OGC 05-096r1, GML 3.1.1 grid CRSs profile
OGC 05-099r2, GML 3.1.1 simple dictionary profile
OGC 08-015, The OpenGIS Abstract Specification, Topic 2: Spatial Referencing by
Coordinates
OGC 05-108r1, Geographic information — Geography Markup Language (GML)2

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OGC 07-092r3

W3C Recommendation January 1999, Namespaces In XML,
http://www.w3.org/TR/2000/REC-xml-names
W3C Recommendation 04 February 2004, Extensible Markup Language (XML) 1.0(Third Edition), http://www.w3.org/TR/REC-xml
W3C Recommendation 2 May 2001: XML Schema Part 0: Primer,
http://www.w3.org/TR/2001/REC-xmlschema-0-20010502/
W3C Recommendation 2 May 2001: XML Schema Part 1: Structures,
http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/
W3C Recommendation 2 May 2001: XML Schema Part 2: Datatypes,
http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/
UCUM, Unified Code for Units of Measure, Schadow, G. and McDonald, C. J. (eds.),
http://aurora.rg.iupui.edu/UCUM
In addition to this document, this Best Practice includes several normative XML
document files. Following approval of this document, these files will be posted online at
the URL http://schemas.openis.net/definitions/. These XML files are also bundled withthe present document. In the event of a discrepancy between the bundled and online
versions of the XML files, the online files shall be considered authoritative.
4

Terms and definitions

For the purposes of this document, the following terms and definitions apply.
4.1
clientsoftware component that can invoke an operation from a server
4.2
document typeclass or structure of a document, which implies its intended application
NOTE
Some document types imply a formal structure or grammar (e.g., schemas, used for document
design and validation), while for other document types the structure is more generally defined (e.g.,
Discussion Papers).

4.3
featureabstraction of a real world phenomena [ISO 19109]
4.4
feature typeclass for all instances of that feature type

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OGC 07-092r3
NOTE

The instances of a class that represents an individual feature type are feature instances.

4.5
interface
named set of operations that characterize the behaviour of an entity [ISO 19119]
4.6
nil
explanation for a void value or other missing information [OGC 05-108r1]
4.7
operation
specification of a transformation or query that an object may be called to execute [ISO19119]
4.8
parameter
variable whose name and value are included in an operation request or response
4.9
phenomenon
feature characteristic, the estimation of which is the purpose of an observation [OGC 05087r2]
NOTE
A phenomenon may be a physical property (such as temperature, length, etc), a classification(such as species), frequency or count, or an existence indication.

4.10
requestinvocation of an operation by a client
4.11
response
result of an operation, returned from a server to a client
4.12
serverservice instancea particular instance of a service [ISO 19119 edited]
4.13
servicedistinct part of the functionality that is provided by an entity through interfaces [ISO19119]
capability which a service provider entity makes available to a service user entity at theinterface between those entities [ISO 19104 terms repository]4

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OGC 07-092r3

4.14
versionversion of an Implementation Standard (document) and XML Schemas to which therequested operation conforms
5

Conventions

5.1

Symbols (and abbreviated terms)

CRS

Coordinate Reference System

EDCS

Environmental Data Coding Standard

EPSG

European Petroleum Survey GroupGML

Geography Markup Language

ISO

International Organization for Standardization

OGC

Open Geospatial Consortium

OWS

OGC Web Service, or Open Web Service

SI

The International System of UnitsTBD

To Be Determined

UCUM

Unified Code for Units of Measure

URI

Universal Resource Identifier

URL

Uniform Resource Locator

URN

Universal Resource NameWCSWeb Coverage Service

WFS

Web Feature Service

WMS

Web Map Service

XML

Extensible Markup Language

1D

One Dimensional

2D

Two Dimensional

3D

Three Dimensional

5.2

Document terms and definitions

The following terms and definitions are used in this document:a) shall – verb form used to indicate a requirement to be strictly followed to conform tothis document, from which no deviation is permitted

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

5OGC 07-092r3b) should – verb form used to indicate desirable ability or use, without mentioning or
excluding other possibilitiesc) may – verb form used to indicate an action permissible within the limits of thisdocumentd) can – verb form used for statements of possibilitye) informative – a part of a document that is provided for explanation, but is not
requiredf)normative – a part of a standards document that is requiredg) annex – an auxiliary part of a document, called an “appendix” in United States
Englishh) clause – a major part of a document, called a “section” or “paragraph” in UnitedStates Englishi)

subclause – a secondary part of a clause or annex, called a “subsection” in UnitedStates English

6

Background

6.1

Definition identifiers

The OGC URN scheme is defined in OGC Document 06-166. It specifies a family ofidentifiers for resources of interest in OGC Web Services, mostly resources provided ordefined by the OGC.
The “def” branch of the OGC URN scheme is defined in this document. This branchprovides standard identifiers for many concepts and definitions. These definitions include
coordinate reference systems and related components, units of measure, nils, and various
object types and definitions. These include definitions and concepts maintained by OGC
and by other authorities who do not provide URNs for their concepts, but which are ofimportance in OGC Web Services and encodings.
The URN syntax is useful because (a) it provides persistent identifiers that are
independent of resource location, while (b) being part of the URI scheme, and thus
compatible with referencing in a web context. A uniform identification scheme is usefulfor interoperability, allowing use of short identifiers for concepts. These identifiers allow
suitable software to make rapid comparisons, and to obtain values from a local cachewhen available, in preference to accessing definitions from a remote service.
6.2

Use for Coordinate Reference Systems

One frequent use is referencing the CRS for an OWS server input or output; another use
is referencing the CRS for a feature geometry or a bounding box. These URNs are used
to identify the referenced CRS, not to transfer a definition of that CRS. Most of this6

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

OGC 07-092r3

material is also applicable to referencing CRS components and Coordinate Operations
and their components, often referred to as objects.
NOTE 1 Subclause D.14 of [OGC 06-121r3] summarizes many of the requirements considered when
specifying how to reference CRSs.

Document [OGC 06-121r3] specifies that each specific OWS shall always reference a
CRS by using a XML attribute or element with the type anyURI. Such an anyURI value
can be used to reference a CRS whether the definition of that CRS is included in the samedata transfer, is NOT included in the same data transfer, cannot be electronicallyaccessed, or can be electronically accessed.
NOTE 2 In XML Schemas, the anyURI data type is the standard way to briefly reference (or cite)something specified elsewhere. XML attributes with the type anyURI include the GML defined attributes
named gml:srsName, gml:uom, xlink:href, and gml:codeSpace.

When using a XML attribute or element with the type anyURI to reference a CRS, CRSrelated, or other object, that URI shall have a value which uses one of two alternative
URI formats:a) Universal Resource Locator (URL), with standard form. The URL format should be
used whenever the referenced definition is known to be electronically available using
this standard URL.
b) Universal Resource Name (URN), with a specified form. The URN format shall be
used whenever the referenced definition is not, or might not be, available using a
URL. This URN shall reference data that is specified by some “authority” and is“well-known” to both client and server software, including multiple clients andmultiple servers.
NOTE 3 Two widely-used forms of URI are URL and URN. We are specifying using URNs as the wayof citing CRS-related definitions that are "well-known" but are not adequately electronically available
using a URL.

Subclause 10.3.2 of the OWS Common standard[OGC 06-121r3] specifies when and how
to use URLs to reference a CRS or CRS-related object. Use of URNs is expected to be
more common than use of URLs, and specific OWS Implementation Standards are
expected to specify many standard URN values.
6.3

Relationships to other identification schemes

6.3.1

URN and URL

URNs [IETF RFC 2141] are a kind of URI [IETF RFC 2396], and may be used as thevalue of references where a URI is required. This is often the case in GML-based
encodings (e.g., the standard XML attributes xlink:href, xlink:role, xlink:arcrole,srsName, uom, codeSpace) and in OGC Web Services (OWS) operation requests andresponses.

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OGC 07-092r3

A URN serves as a persistent identifier of a resource or concept. A detailed description of
the resource may also be available online, with a resource locator (URL) providing anaccess point. In general, there is no direct mapping or algorithm to obtain a URL for the
resource designated by a URN. URNs are intended to be more persistent than URLs, sothat they remain valid even if a resource description is relocated. However, a resolution
service or resolver may provide a URL corresponding to a URN.
NOTE
In the future it is expected that the OGC Network will provide a resolution service for URNs in
the OGC scheme.

6.3.2

URN and schema component designators

In a few places in OWS interfaces, an identifier for an XML component is required. In
these cases, it is important that the identifier reference the actual schema definition,
which may then be used as the template for an OWS request or response.
A number of options are available for identification of schema components. The W3C
XML Schema recommendation provides QName (qualified name – see XML SchemaPart 2, clause 3.2.18). A QName has the lexical form ns:name where “ns” is an XML
namespace prefix for which a namespace declaration is in scope. The QName thus
corresponds with an identifier tuple {namespace, local name} where “namespace” is the
fully scoped identifier for the XML namespace. In contrast, a URN identifier is complete,and does not depend on context for resolution of the namespace prefix.
NOTE
The W3C XML activity is currently considering a more complete scheme for identification ofschema components, documented in the working draft XML Schema: Component Designators [9].

In OWS interfaces, XML components are generally identified using a QName.
While there is some overlap of the meaning of schema component designators with the
OGC URN scheme used for dataTypes (clause 8.5) and featureTypes, it should beunderstood that a URN identifies the concept, and not just its XML and XML Schema
implementation. Of course, the concepts denoted by identifiers from the featureTypebranch generally have XML Schema implementations, so direct mappings are implied.
Note that the mapping may be one-to-many, for example to manage versioning of the
XML schema implementation independent of versioning of the concept.
Table 10 in Subclause 8.5 provides definitions in the dataType branch, together withmappings to a QName designation of equivalent XML schema components. That
subclause provides the complete definition of URNs in the dataType branch, since“OGC” is the only authority recognised for this branch.
For the featureType branch, it is expected that many authorities will have an interest in
using the “def” branch of the OGC URN scheme to provide feature type identifiers. It is
incumbent on each authority to indicate the mapping from the URN form of identifier toother schema component designators, such as a QName, so that the use of these in OWS
interfaces is unambiguous.

8

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OGC 07-092r3

7
7.1

OGC URN scheme for definitions
OGC URN scheme

The OGC URN scheme is defined in OGC Document 06-166. It specifies a family ofidentifiers for resources of interest in the context of OGC Web Services, mostly
concerning resources provided or defined by OGC. The OGC scheme has the form
urn:ogc:{category.label}:{ResourceSpecificString}
The category.label must be one of a set of values that are not yet specified, except that
this document specifies the “def” value and the corresponding ResourceSpecificString
format.
7.2

URNs for single objects

To identify the definition of a single object, the URN shall have the form:
urn:ogc:def:objectType:authority:version:code

The “urn”, “ogc”, “def”, and six “:” parts of this URN are fixed. The “ogc” part shall be
the registered namespace authority for all URNs used by the OGC. The “def” part shallbe the fixed category label which identifies all the OGC URNs that reference object
definitions. The “objectType” part shall be an OGC-specified unique-identifier of thetype of the referenced definition.
NOTE 1 The ”ogc” part denotes the namespace authority in a URN, and the value used should be
registered with IANA. Pending the official registration of the OGC scheme with IETF/IANA, the value “xogc” should be used, where the “x” denotes an experimental namespace. The “def” part is a value for the{category.label} part specified in [OGC 06-166]. The remaining “objectType:authority:version:code” parts
are values of the {ResourceSpecificString} part specified in [OGC 06-166].

The “objectType” part shall be the OGC-specified token for the type of concept identified
by the URN.
NOTE 2 The set of object types denoted by the OGC URN scheme is currently specified normatively in
Table 2 in this document and revisions. In the future it is expected that this mechanism will be replaced bya dynamic registry.

The “authority” part shall be the OGC-specified abbreviation for the authority
organization that specified the referenced definition.
NOTE 3 The set of authorities recognised for the purposes of the OGC URN scheme is currently
specified normatively in Table 1 in this document. In future it is expected that this mechanism will be
replaced by a dynamic registry.

The optional “version” part shall be the version of the authority or code for the referenced
definition. The “code” part shall be a unique identifier of the referenced definition, as
specified by the referenced authority. The “code” part can be human-understandable,
provided that it is unique for that authority, version, and objectType. In this use, all
textual parts of URN values shall be case-insensitive.

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9OGC 07-092r3

The “version” part of these URNs can be omitted when the referenced definition does nothave a version, and the referenced definition is not specific to an authority version. When
included, the “version” shall be recorded in the format specified by the authority. The
version format is sometimes “N.N.N” or “N.N”, where each “N” stands for an integer. If
no other version identification is provided by the authority, a year or other date can beused. No "v" or other version prefix shall be included.
The required “authority” part identifies an authority recognized by the OGC, and theallowed “authority” values shall include those listed in Table 1. In this table, the thirdcolumn references a specification for each "authority" value. All URNs that include this"authority" value shall mean exactly what is meant by that specification, when thecorresponding “code” and “version” values are used.
EXAMPLEThe URN value urn:ogc:def:crs:EPSG:6.6:4326 shall mean the Coordinate Reference
System (CRS) with code 4326 specified in version 6.6 of the EPSG database available at
http://www.epsg.org/. That CRS specifies the axis order as Latitude followed by Longitude.

10

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OGC 07-092r3

Table 1 — “authority” values for definitions in OGC URN namespace“authority”
value

Referenced authority

Reference tospecification

Use for“code” value

EDCS

Environmental Data
CodingSpecification a

ISO/IEC 18025:2005

Label or Codecolumn value f

2005

EPSG

EPSG database b

http://www.epsg.org/

EPSG numeric
identifier value

Databaseversion

OGC

Open Geospatial
Consortium c

Clause 8 g

Values specified
in Clause 8 g

Values specified
in Clause 8 g

SIInternational System
of Units d

ISO 1000:1992,2000

http://www.bipm.fr/en/si/Values from
Symbol columnof tables hUnified Code for
Units of Measure e

http://aurora.regenstrief.org/UCUM“Case sensitive”
form of code i

none

UCUM

Use for“version” value

a The Environmental Data Coding Specification (EDCS) is recognized as an authority that specifies a
vocabulary of phenomena in its Attributes dictionary (“EAs”).
b The EPSG database is now maintained by the OGP Surveying and Positioning Committee, and isrecognized as an authority that specifies many CRS-related definitions.
c The Open Geospatial Consortium (OGC) recognizes itself as one or more authorities, here using “OGC” as
the one current authority abbreviation.
d The International System of Units (SI) is recognized as an authority that specifies basic units of measure
and a limited selection of derived units.
e The Unified Code for Units of Measure (UCUM) is recognized as an authority that specifies symbols fordenoting a large set of basic units of measure and a grammar that defines combinations of these that correspondwith symbols that are commonly used in commerce, scientific and engineering applications.
fValues from the Label or Code columns of the attribute Tables 6.5 – 6.30 of ISO/IEC 18025:2005.

g The OGC shall explicitly specify each “code” and “version” value defined by the “OGC” authority. Clause
8 of this document specifies some of these codes and versions. Additional OGC codes and versions are now
specified in Clause 10 of OGC 05-096r1, and more can be specified in future OGC Implementation
Specifications and Best Practices Papers.
h Plus combinations of symbols as defined in the SI specification. Note that some symbols include elementsthat are not available on a standard character entry device (e.g. , °C). For these units, it is recommended that
the UCUM symbol and URN be used in preference. See also footnote i.
i UCUM specifies code values or symbols using the reduced character set universally available on character
entry devices (“7-bit ascii"), and combinations of these generated using the grammar described in the UCUM
specification. For this reason the use of UCUM codes is preferred to those specified in ISO 31:1992 [8], as thelatter specifies the use of superscripts and non-latin symbols for certain units. While these are in principle
supported by Unicode, for practical reasons the reduced character-set encoding is preferred for use in the URN
syntax.

The required “objectType” part identifies the type of the referenced definition, and theallowed “objectType” values shall include those listed in Table 2.

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Table 2 — “objectType” values for definitions in OGC URN namespace“objectType” value

URN references

Object type defined inaxis

coordinate system axis definition

9.3 in OGC 08-015

axisDirection

axis direction code definition

9.4 in OGC 08-015

coordinateOperation

coordinate operation definition

11.1 in OGC 08-015

crs

coordinate reference system definition

8.2 in OGC 08-015

cs

coordinate system definition

9.2 in OGC 08-015

datum

datum definition

10.1 in OGC 08-015

dataType

data type definition

D.1 in OGC 05-007r4

derivedCRSTypederived CRS type code definition

8.3 in OGC 08-015

documentType

document type definition

4. in OGC 05-020r4

ellipsoid

ellipsoid definition

10.2.2 in OGC 08-015

featureType

feature type definitionas specified in an application
schema (ISO 19109)

group

operation parameter group definition

11.2 in OGC 08-015

meaning

parameter meaning definition

D.1 in OGC 05-007r4

meridianprime meridian definition

10.2.1 in OGC 08-015

methodoperation method definition

11.2 in OGC 08-015

nilexplanations for missing information

8.2.3.1 in OGC 05-108r1

parameter

operation parameter definition

11.2 in OGC 08-015

phenomenon

observable property definition

6.2 in OGC 05-087r2

pixelInCell

Pixel in cell code definition

10.3 in OGC 08-015

rangeMeaning

range meaning code definition

9.4 in OGC 08-015

referenceSystem

value reference system definition

D.1 in OGC 05-007r4

uom

unit of measure definition

verticalDatumTypevertical datum type code definition

10.3 in OGC 08-015

Specializing the above, the URN value for an anyURI that references one object in theEuropean Petroleum Survey Group (EPSG) database should have the form:
urn:ogc:def:objectType:EPSG::code

In this case, the “authority” part of a URN shall be “EPSG”. The “code” part of a URN
should be the EPSG “code” unique identifier of the referenced definition. Alternately, the“code” part of a URN can be the EPSG “name” unique identifier. It is recommended toomit the version number, as this is not required to identify a referenced record in the
EPSG dataset and may even lead to confusion.

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NOTE 2 The policy of the OGP Survey and Positioning Committee is to not delete any entities.
However, if a record is found to be incorrect, that record is deprecated and replaced. When this is done, thedeprecation field of the deprecated record is changed from "false" to "true". (In some implementations,"false" may be "0" or "no", and "true" may be "1" or "yes"). Deprecated records are also termed ‘invalid
records’ When retrieving any geodetic parameters from the EPSG dataset a user therefore needs to verify
whether the record(s) is / are valid or invalid. The user then has two options: (1) to follow the links
provided and use the valid replacing record(s), a course typically followed when spatially referencing a
new dataset, or (2) retrieve the invalid, deprecated record(s) in order to undo the effects of this error in anexisting spatial dataset that had been spatially referenced using the incorrect records. Note that spatialreferencing using (an) invalid EPSG entities will only generate errors if the data is subsequently subjected
to coordinate conversions and/or transformations.
Example 1

The URN value for CRS 2984 is:

urn:ogc:def:crs:EPSG::2984.

However, this entity has been deprecated and has been replaced by CRS 3163:
urn:ogc:def:crs:EPSG::3163.

Example 1
The URN value for the “WGS 84 longitude-latitude” CRS specified in Subclause B.3 of
WMS 1.3 (previously referenced as “CRS:84”) is:
urn:ogc:def:crs:OGC:1.3:CRS84

7.3

URN extensions for OGC

The following Subclauses 7.4 and 7.5 extend the normal uses of URNs to meet OGC
needs, primarily for referencing Coordinate Reference Systems. One URN is required touniquely and persistently identify one resource. Normally each URN value is opaque to
URN users, and the sets of URNs and corresponding resources are both enumerable andperistent. The following URN extensions allow a non-enumerable (sometimes infinite)
set of URNs to reference the corresponding non-enumerable set of (OGC) resources. The
specific URNs and corresponding resources that are currently in use is expandable toother members of these non-enumerable sets.
NOTE 1 A non-enumerable set of URNs with the corresponding non-enumerable set of resources can beconsidered to be “virtual”, not being implemented until needed. When needed, a specific URN in this set
can be automatically instantiated with its corresponding resource. Given a specific URN in such a nonenumerable (sometimes infinite) set of URNs, the corresponding specific resource in the corresponding
non-enumerable set of resources can be automatically instantiated. Or given a specific resource in such a
non-enumerable set of resources, the corresponding specific URN in the corresponding non-enumerable setof URNs can be automatically instantiated. Except for automatic implementation of the corresponding
resource, these specific URNs can be used just like normal URNs, to uniquely, opaquely, and persistently
identify the one corresponding resource. Only the appropriate URN resolution and registration service(s)need to know about the virtual nature of these sets of URNs with the corresponding set of resources.
NOTE 2 An extended URN can also be considered to be “parameterized”, with parameter values in the
URN value being used as specific values for the corresponding parameters in a corresponding
parameterized resource. Again, only the appropriate URN resolution and registration service(s) need toknow about the parameterized nature of these sets of URNs with the corresponding set of resources. Eachspecific URN is opaque to URN users, and the associated specific resource is persistent (but not necessarily
stored, or stored at fixed locations).

Each URN in such a non-enumerable set opaquely references the corresponding resourcein such a non-enumerable set, where this correspondence is persistent (or fixed) althoughneither set is enumerable. That is, only the appropriate URN resolution and

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OGC 07-092r3

creation/registration service(s) need to know that a non-enumerable set of URNs isreferencing the corresponding non-enumerable set of resources. A URN resolution
service can take any specific URN in such a non-enumerable set of URNs andautomatically instantiate the corresponding specific resource in the corresponding nonenumerable set of resources. A URN registration service can take any specific resource
which falls in such a non-enumerable set of resources and automatically instantiate thecorresponding specific URN in the corresponding non-enumerable set of URNs. Eachspecific URN is opaque to URN users, and the associated specific resource is persistent(but not necessarily stored, or stored at fixed locations).
7.4

URNs for not-completely-specified objects

A URN can also be used to denote a not-completely-specified object, which is specified
without the values of a few identified parameters. In this case, the URN value includes
the values for each identified parameter. To identify an object with two unspecified
parameters, the URN shall have the form:
urn:ogc:def:objectType:authority:version:code:value1:value2
NOTE 1 Not-completely-specified objects are very useful when many similar objects are needed,
especially when the possible values of the distinguishing parameters cannot be enumerated.
EXAMPLE 1
Subclause 6.7.3.4 and Annex B of WMS 1.3.0 specify five not-completely-specified map
projections, where the parameters specify the central meridian, etc.
EXAMPLE 2
Clause 7 of [OGC 05-096r1] specifies two not-completely-specified unrectified image
CRSs, where the single parameter specifies the image identifier.

In this URN form, the values for the previously-identified parameters are added to the
URN form for a single object, as specified above. The obvious variations on the URI
form can be used when one or three parameters are unspecified. The object identified by
the “authority”, “version”, and “code” must be completely specified with the exception of
the values for a few clearly identified parameters. Whenever such a parameter value
requires a unit of measure (uom), the uom for that parameter shall be specified by thereferenced not-completely-specified object.
EXAMPLE 3
The URN value for the Auto Orthographic CRS 42003 specified in Subclauses
6.7.3.4 and B.9 of WMS 1.3.0 is:
urn:ogc:def:crs:OGC:1.3:AUTO42003:1:-100:45

NOTE 2 Additional examples of not-completely-specified objects are specified in Subclauses B.7, B.8,
B.10, and B.11 of WMS 1.3.0, and in Subclauses 10.1 through 10, 3 of [OGC 05-096r1].

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OGC 07-092r3
7.5

URNs for combined objects

7.5.1

Overview

In some cases, it is useful to reference two or more well-known objects that are
combined, where the combination is specified at run time. Such combining of two or
more well-known objects shall only be used when all of the following conditions are true:a) The objects being combined are correct for the combination being formed, as theseobjects are specified in [OGC 08-015] for CRS-related objects.
b) This combination of objects is not an existing well-known object, such as specified in
the EPSG database or a geodetic parameter dataset of an acknowledged alternative
authority.
NOTE 1 If combining two or more well-known objects, please ask if this combination will be frequently
used. If combining only EPSG codes because EPSG has not populated this combination, please send arequest for this combination to the EPSG if this combination is likely to be frequently used. Similarly, if
combining OGC codes, by themselves or with EPSG codes, please suggest that this combination be added
to the OGC codes, if this combination is likely to be frequently used.

c) The objects being combined are all in the “ogc” URN namespace, preferably all
defined by the same authority (e.g., EPSG or OGC).
NOTE 2 If objects specified by different authorities are combined, there is higher risk that these objects
are not compatible. For example, some authorities might specify objects different from [OGC 08-015].

d) Using a URN for the combination is desirable, since it is not convenient to combine
these objects in an XML document based on GML, and then reference this document
using a URL (as specified in Subclauses 10.3.1 and 10.3.2 of [OGC 06-121r3]).
A URN that identifies a definition that is itself defined by combining two or more objects
shall be constructed by concatenating the URNs of the two individual objects into one
URN, as follows:
urn:ogc:def:objectType,objectType:authority:version:code,
objectType:authority:version:code

Similarly, an identifier can concatenate the URNs of the three individual objects, using
the URN form:
urn:ogc:def:objectType,objectType:authority:version:code,
objectType:authority:version:code,objectType:authority:version:code
NOTE 3 When URNs are concatenated like this, the combined object is implicitly defined, and is not
assigned a single object “code”. That is, the defined object has no single code.

In a concatenated URN, the first “objectType” is the type of the combined object.
Combined references in a URN can be used for defining several types of objects, as
specified by specific Implementation Standards, including for:Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

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OGC 07-092r3a) Compound coordinate reference systemsb) Concatenated operationsc) Projected and derived coordinate reference systemsd) Combining a datum and a coordinate system into a coordinate reference systeme) Objects defined by specific Implementation Standards
The first four combinations listed above are described in the following subclauses.
7.5.2

URN combined references for compound coordinate reference systems

A URN reference to combined objects can be allowed for any compound coordinate
reference system (CompoundCRS) that combines two or three well-known CRSs. In thiscase, the URN shall concatenate the URNs of the two or three individual well-known
CRSs. This combining is allowed only when all the conditions specified in Subclause
7.3.1 are met.
The URNs of the individual well-known CRSs shall be listed in the same order in which
the individual coordinate tuples are combined to form the CompoundCRS
coordinate tuple. All the “objectType” values shall be “crs”.
EXAMPLE The URN value for combining the CRSs: EPSG 4269 (NAD83) and EPSG 5713 (Canadian
Geodetic Vertical Datum of 1928 height is:
urn:ogc:def:crs,crs:EPSG::4269,crs:EPSG::5713

7.5.3

URN combined references for concatenated operations

A URN reference to combined objects can be allowed for any concatenated coordinate
operation (ConcatenatedOperation) that combines two or more well-known coordinate
operations. In this case, the URN shall concatenate the URNs of the two or more wellknown coordinate operations. This combining is allowed only when all the conditions
specified in Subclause 7.3.1 are met.
NOTE 1 In particular, the coordinate operations concatenated must meet the stated constraint: The
sequence of operations is constrained by the requirement that the source coordinate reference system ofstep (n+1) must be the same as the target coordinate reference system of step (n). The source coordinate
reference system of the first step and the target coordinate reference system of the last step are the source
and target coordinate reference system associated with the concatenated operation.
NOTE 2 In a well-known dataset, a CoordinateOperation may be registered only in one direction, withthe reverse operation being implied. This means that the roles of source and target CRS may have to be
swapped if an implied-reverse CoordinateOperation is included in a ConcatenatedOperation. In this case,the swapped source and target CRS shall satisfy the above constraint.

The URNs of the individual coordinate operations shall be concatenated in the order ofcoordinate operation application. The “objectType” values shall all be“coordinateOperation”.

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OGC 07-092r3
EXAMPLEThe URN value for combining the EPSG XXXX and EPSG YYYY coordinate operationsis:urn:ogc:def:coordinateOperation,coordinateOperation:EPSG::XXXX,coordinateOperation:EPSG::YYYY

7.5.4

URN combined references for projected or derived CRSs

A URN reference to combined objects can be allowed for any projected coordinate
reference system (ProjectedCRS) that combines a well-known GeographicCRS and awell-known (defined by) Conversion. In this case, the URN shall concatenate the URNsof the one well-known CRS, one well-known Conversion, and one well-known
CartesianCS. This combining is allowed only when all the conditions specified in
Subclause 7.3.1 are met.
Similarly, a URN reference to combined objects can be allowed for any derived
coordinate reference system (DerivedCRS) that combines a well-known base CRS, awell-known CoordinateSystem, and a well-known (defined by) Conversion.
The URNs of the individual components of the projected or derived CRS shall be listed
in the order of GeographicCRS, CS, and then Conversion. The four “objectType” values
shall be “crs”, “crs”, “cs”, and “coordinateOperation”.
EXAMPLEThe URN value for combining the EPSG XXXX CRS, EPSG YYYY CS, and EPSGZZZZ Conversion to define a custom projected or derived CRS is:
urn:ogc:def:crs,crs:EPSG::XXXX,cs:EPSG::YYYY,coordinateOperation:EPS
G::ZZZZ

7.5.5

URN combined references for datum and coordinate system

A URN reference to combined objects can be allowed for a coordinate reference systemthat combines a well-known datum with a well-known coordinate system. In this case,the URN shall concatenate the URNs of one well-known datum and one well-known
coordinate system. This combining is allowed only when all the conditions specified in
Subclause 7.3.1 are met.
The URNs of the individual components shall be listed in the order of datum and thencoordinate system. The three “objectType” values shall be “crs”, “datum” and “cs”.
EXAMPLEThe URN value for combining the EPSG XXXX datum and EPSG YYYY coordinate
system to define a custom CRS is:
urn:ogc:def:crs,datum:EPSG::XXXX,cs:EPSG::YYYY88.1

URN values for definitions and concepts in ogc namespace
Introduction

This clause provides the normative specification and URNs for some specific object
definitions defined by the OGC. Additional definitions in the “ogc” URN namespace will

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OGC 07-092r3

be specified in other OGC documents. For example, more URNs are specified in
Subclause 7.1 of the GML grid CRSs profile [OGC 05-096r1].
NOTE
Many examples of “ogc” URN use for object definitions are contained in the GML examples inAnnex A of this document, in Clause 7 of [OGC 05-096r1], and in Clause 6 of [OGC 05-095r1].

8.2

CRS definitions

The definitions of Coordinate Reference Systems (CRSs) defined by the OGC shall use
the URNs listed in Table 3. The URN parts shown as “99” ands “8888” represent
numbers that shall be substituted for the specified parameter values. All of these CRSs
are defined in Annex B of WMS 1.3 [OGC 06-042].
Table 3 — URNs for CRSs defined by OGC
URN

CRS name

Definition reference

urn:ogc:def:crs:OGC:1.3:CRS1

Map CS

B.2 in OGC 06-042

urn:ogc:def:crs:OGC:1.3:CRS84

WGS 84 longitude-latitude

B.3 in OGC 06-042

urn:ogc:def:crs:OGC:1.3:CRS83

NAD83 longitude-latitude

B.4 in OGC 06-042

urn:ogc:def:crs:OGC:1.3:CRS27

NAD27 longitude-latitude

B.5 in OGC 06-042

urn:ogc:def:crs:OGC:1.3:CRS88

NAVD 88

B.6 in OGC 06-042

urn:ogc:def:crs:OGC:1.3:AUTO42001:99:8888

Auto universal transverse mercator

B.7 in OGC 06-042

urn:ogc:def:crs:OGC:1.3:AUTO42002:99:8888

Auto transverse mercator

B.8 in OGC 06-042

urn:ogc:def:crs:OGC:1.3:AUTO42003:99:8888

Auto orthographic

B.9 in OGC 06-042

urn:ogc:def:crs:OGC:1.3:AUTO42004:99:8888

Auto equirectangular

B.10 in OGC 06-042

urn:ogc:def:crs:OGC:1.3:AUTO42005:99

Auto Mollweide

B.11 in OGC 06-042

8.3

CRS code list values definitions

The definitions of the standard values for the five CodeList stereotyped classes specified
in Tables 9, 31, 32, 37, and 39 of OGC Abstract Specification Topic 2 [OGC 08-015]
shall use the URNs listed in Tables 2 through 6. The definitions of these values shall be
as specified in the XML documents in Subclauses A.2 through A.6.

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Table 4 — URNs for derivedCRSType values
URN

Value

Brief definition

urn:ogc:def:derivedCRSType:OGC:1.0:geodetic

geodetic

A coordinate reference system based on ageodetic datum

urn:ogc:def:derivedCRSType:OGC:1.0:verticalverticalA coordinate reference system used for recordingof heights or depths.

urn:ogc:def:derivedCRSType:OGC:1.0:engineeringengineering

A contextually local coordinate reference
system.

urn:ogc:def:derivedCRSType:OGC:1.0:image

image

An engineering coordinate reference systemapplied to locations in images.

urn:ogc:def:derivedCRSType:OGC:1.0:temporal

temporalA reference system used for the recording oftime.

Table 5 — URNs for verticalDatumType values
URN

Value

Brief definition

urn:ogc:def:verticalDatumType:OGC:1.0:geoidal

geoidalZero value of vertical axis approximates aconstant potential surface, usually the geoid.

urn:ogc:def:verticalDatumType:OGC:1.0:depth

depth

Zero value of vertical axis has meaning for
purpose which measurements are used for

urn:ogc:def:verticalDatumType:OGC:1.0:barometricbarometricAtmospheric pressure is basis for thedefinition of origin of vertical axis

urn:ogc:def:verticalDatumType:OGC:1.0:otherSurface

otherSurface

Other variations to above three vertical
datum types.

NOTE
The verticalDatumType existed in the previous version of OGC Abstract Specification Topic 2[OGC 04-046r3], but has been removed in the new version [OGC 08-015]. The verticalDatumType is thus
included in GML 3.1.1, but not in GML 3.2 [OGC 05-108r1].

Table 6 — URNs for pixelInCell values
URN

Value

Definition

urn:ogc:def:pixelInCell:OGC:1.0:cellCenter

cellCenter

The origin of the image coordinate system isat the centre of a grid cell or image pixel.

urn:ogc:def:pixelInCell:OGC:1.0:cellCorner

cellCorner

The origin of the image coordinate system isat the corner of a grid cell, or half-way
between the centres of adjacent image pixels.

Table 7 — URNs for rangeMeaning values
URN

Value

Brief definition

urn:ogc:def:rangeMeaning:OGC:1.0:exact

exact

Any value between and including minimumValueand maximiumValue is valid.

urn:ogc:def:rangeMeaning:OGC:1.0:wraparoundwraparound

The axis is continuous with values wrapping
around at the minimumValue and maximumValue.

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OGC 07-092r3

Table 8 — URNs for axisDirection values
URN

Value

Brief definition

urn:ogc:def:axisDirection:OGC:1.0:northnorthAxis positive direction is north.

urn:ogc:def:axisDirection:OGC:1.0:northNorthEast

northNorthEast

Axis positive direction is approximately northnorth-east.

urn:ogc:def:axisDirection:OGC:1.0:northEast

northEast

Axis positive direction is approximately northeast.

urn:ogc:def:axisDirection:OGC:1.0:eastNorthEast

eastNorthEast

Axis positive direction is approximately eastnorth-east.

urn:ogc:def:axisDirection:OGC:1.0:east

east

Axis positive direction is π/2 radians clockwisefrom north.

urn:ogc:def:axisDirection:OGC:1.0:eastSouthEast

eastSouthEast

Axis positive direction is approximately eastsouth-east.

urn:ogc:def:axisDirection:OGC:1.0:southEast

southEast

Axis positive direction is approximately southeast.

urn:ogc:def:axisDirection:OGC:1.0:southSouthEast

southSouthEast

Axis positive direction is approximately southsouth-east.

urn:ogc:def:axisDirection:OGC:1.0:south

south

Axis positive direction is π radians clockwisefrom north.

urn:ogc:def:axisDirection:OGC:1.0:southSouthWest

southSouthWest

Axis positive direction is approximately southsouth-west.

urn:ogc:def:axisDirection:OGC:1.0:southWest

southWest

Axis positive direction is approximately southwest.

urn:ogc:def:axisDirection:OGC:1.0:westSouthWest

westSouthWest

Axis positive direction is approximately westsouth-west.

urn:ogc:def:axisDirection:OGC:1.0:west

west

Axis positive direction is 3π/2 radiansclockwise from north.

urn:ogc:def:axisDirection:OGC:1.0:westNorthWest

westNorthWest

Axis positive direction is approximately westnorth-west.

urn:ogc:def:axisDirection:OGC:1.0:northWest

northWest

Axis positive direction is approximately northwest.

urn:ogc:def:axisDirection:OGC:1.0:northNorthWest

northNorthWest

Axis positive direction is approximately northnorth-west.

urn:ogc:def:axisDirection:OGC:1.0:up

up

Axis positive direction is up relative to gravity.

urn:ogc:def:axisDirection:OGC:1.0:down

down

Axis positive direction is down relative togravity.

urn:ogc:def:axisDirection:OGC:1.0:geocentricX

geocentricX

Axis positive direction is in the equatorial planefrom centre of modelled earth towards
intersection of equator with prime meridian.

urn:ogc:def:axisDirection:OGC:1.0:geocentricY

geocentricY

Axis positive direction is in equatorial planefrom centre of the modelled earth towards
intersection of equator and meridian π/2 radianseastwards from prime meridian.

urn:ogc:def:axisDirection:OGC:1.0:geocentricZ

geocentricZ

Axis positive direction is from centre ofmodelled earth parallel to its rotation axis andtowards its north pole.

urn:ogc:def:axisDirection:OGC:1.0:future

futureAxis positive direction is towards the future.

urn:ogc:def:axisDirection:OGC:1.0:past

past

Axis positive direction is towards the past.

urn:ogc:def:axisDirection:OGC:1.0:columnPositive

columnPositive

Axis positive direction is towards higher pixel
column.

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URN

Value

Brief definition

urn:ogc:def:axisDirection:OGC:1.0:columnNegative

columnNegative

Axis positive direction is towards lower pixel
column.

urn:ogc:def:axisDirection:OGC:1.0:rowPositive

rowPositive

Axis positive direction is towards higher pixelrow.

urn:ogc:def:axisDirection:OGC:1.0:rowNegative

rowNegative

Axis positive direction is towards lower pixelrow.

urn:ogc:def:axisDirection:OGC:1.0:displayRightdisplayRight

Axis positive direction is right in display.

urn:ogc:def:axisDirection:OGC:1.0:displayLeft

displayLeft

Axis positive direction is left in display.

urn:ogc:def:axisDirection:OGC:1.0:displayUpdisplayUp

Axis positive direction is towards top of
approximately vertical display surface.

urn:ogc:def:axisDirection:OGC:1.0:displayDown

displayDown

Axis positive direction is towards bottom ofapproximately vertical display surface.

NOTE There is some overlap with the axis directions defined in the EPSG dataset, but this is not
perceived to create any problems for users.

8.4

Unit-of-measure (uom) definitions

The definitions of some units-of-measure which are defined by the OGC shall use the
URNs listed in Table 9. The definitions of these units shall be as specified in the XML
document in Subclause A.7. Most of these units are also specified by the EPSG, as listed.
Table 9 — URNs for units-of-measure
OGC URN

Meaning

Quantity typeEPSG URN

urn:ogc:def:uom:OGC:1.0:degree

Angular degree

angle

urn:ogc:def:uom:EPSG::9102

urn:ogc:def:uom:OGC:1.0:radian

Angular radian

angle

TBD

urn:ogc:def:uom:OGC:1.0:metre

Length metre

lengthurn:ogc:def:uom:EPSG::9001

urn:ogc:def:uom:OGC:1.0:unity

unitless ratio of two
quantities with thesame units

scale factor

urn:ogc:def:uom:EPSG::8805

8.5

Data type definitions

URNs are useful to identify data types in multiple OGC Implementation Standards. These
uses include in the ows:DataType (metadata) element in the ows:DomainType in the newversion of the OWS Common Implementation Standard [OGC 06-121r3]. The OGCspecified URNs that can be used for identifying data types (expected to be used in
multiple OGC Implementation Standards) shall include those listed in Table 10. The left
column lists each URN specified here, and the centre column lists the definition whichshall be used for that URN.
Use of these URNs is not limited to data encoded in XML, or even to use of these URNs
in XML-encoded documents. When data is encoded in XML, the right column in thistable lists an XML Schema (XSD) or Geometry Markup Language (GML) version 3.1.1
identifier that can be used to encode that data type. More complete definitions of some ofthese data types are specified in the XML document in Subclause A.8.

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OGC 07-092r3

Table 10 — URNs for data types
XSD/GML data type a

OGC URN

Brief definition

urn:ogc:def:dataType:
OGC:1.1:crsURI

URI used to reference a Coordinate Reference
System (CRS)

xsd:anyURI

urn:ogc:def:dataType:
OGC:1.1:anyURI

URI used for any other purpose

xsd:anyURI

urn:ogc:def:dataType:
OGC:1.1:measure

General numeric value of a quantity, with its
associated unit of measure

gml:MeasureTypeurn:ogc:def:dataType:
OGC:1.1:length

Value of a length (or distance) quantity, with its
units

gml:LengthTypeurn:ogc:def:dataType:
OGC:1.1: scale

Value of a scale factor (or ratio) that has no
physical unit

gml:ScaleTypeurn:ogc:def:dataType:
OGC:1.1: time

Value of a time or temporal quantity, with its
units

gml:TimeTypeurn:ogc:def:dataType:
OGC:1.1:gridLength

Value of a length (or distance) quantity in a grid,where the grid spacing does not have any
associated physical units, or does not have aconstant physical spacing b

gml:GridLengthTypeurn:ogc:def:dataType:
OGC:1.1:angle

Value of an angle quantity, with its units

gml:AngleTypeurn:ogc:def:dataType:
OGC:1.1:lengthOrA
ngle

Value of a length or angle quantity, with its units,
sometimes used for horizontal groundcoordinates

gml:MeasureTypeurn:ogc:def:dataType:
OGC:1.1:string

String value a quantity c

xsd:string

urn:ogc:def:dataType:
OGC:1.1:positiveInt
eger

Positive integer value of a quantity, usually used
for a count c

xsd:positiveInteger

urn:ogc:def:dataType:
OGC:1.1:nonNegati
veInteger

Zero or positive integer values of a quantity c

xsd:nonNegativeInteger

urn:ogc:def:dataType:
OGC:1.1:boolean

Boolean value of a quantity c

xsd:boolean

urn:ogc:def:dataType:
OGC:1.1:measureLi
stOrdered sequence of two or more numeric valuesof a list of general measures dgml:MeasureListTypeurn:ogc:def:dataType:
OGC:1.1:lengthList

Ordered sequence of two or more numeric valuesof a list of Length measures dgml:MeasureListTypeurn:ogc:def:dataType:
OGC:1.1:scaleList

Ordered sequence of two or more numeric valuesof a list of Scale measures

gml:MeasureListTypeurn:ogc:def:dataType:
OGC:1.1:angleList

Ordered sequence of two or more numeric valuesof a list of Angle measures dgml:MeasureListType

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OGC 07-092r3
XSD/GML data type agml:MeasureListType

OGC URN

Brief definition

urn:ogc:def:dataType:
OGC:1.1:timeList

Ordered sequence of two or more numeric valuesof a list of Time measures durn:ogc:def:dataType:
OGC:1.1:gridLength
List

Ordered sequence of two or more numeric valuesof a list of Grid Length measures dgml:MeasureListTypeurn:ogc:def:dataType:
OGC:1.1:integerList

Ordered sequence of two or more integer valuesof a list, usually used for counts

gml:integerList

urn:ogc:def:dataType:
OGC:1.1:positiveInt
egerList

Ordered sequence of two or more positive integer
values of a list, usually used for counts e

gml:integerList

urn:ogc:def:dataType:
OGC:1.1:valueFile

URN reference to file or part of a file containing
one or more parameter values, each numericvalue with its associated unit of measure

gml:valueFile

urn:ogc:def:dataType:
OGC:1.1:anyCRS

Definition of any Coordinate Reference System

Any concrete elementin substitution groupheaded by
gml:AbstractCoordin
ateReferenceSystemaThis data type is stated as a qualified name (QName). The two namespaces used here are:xmlns:gml=”http://www.opengis.net/gml”
xmlns:xsd=”http://www.w3.org/2001/XMLSchema”

b This grid length will often be used in a digital image grid, where the base units are likely to be pixel
spacings.
c

Does not have an associated unit of measure.

d Each value shall have the same associated unit of measure. An element of this type contains a spaceseparated list of double values with one associated unit of measure.
e An element of this type contains a space-separated list of integer values, without an associated unit ofmeasure.

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OGC 07-092r3

Annex A(normative)
GML dictionaries of OGC definitions

A.1

Introduction

This annex provides XML documents that specify the definitions of some of the objects
assigned “ogc” URN values in Clause 8. Except for units-of-measure, these definitions
are encoded in XML using the GML 3.1.1 simple dictionary profile [OGC 05-099r2].
The unitsDictionary is encoded in XML using coordinateReferenceSystems.xsd fromGML 3.1.1.
NOTE
All of these definitions also could be encoded using the gml:Dictionary element fromdictionary.xsd in GML 3.1.1. The XML documents could be identical except for referencing dictionary.xsd
in GML 3.1.1 instead of referencing the GML 3.1.1 simple dictionary profile.

These XML-encoded document files may be bundled in a zip file with this document.
These XML files are also posted online at the URL
http://schemas.opengeospatial.net/definitions/, in a lower level directory used for thisVersion of this document. In the event of a discrepancy between the bundled and online
versions of these XML files, the online files shall be considered authoritative.
A server may reference an exact copy of these documents located elsewhere, as long as
they are readily accessible by clients. For example, it may be desirable to place thereferenced documents on the same network server as an OWS instance, since that
decreases the number of points of possible network failure. Such local copies should beorganized into directories similar to http://schemas.opengeospatial.net/. The server ownershall insure that any such local copies are kept up-to-date with respect to the authoritative
files at http://schemas.opengeospatial.net/.
A.2

Definitions of derivedCRSType values

The definitions of the derivedCRSType standard values used in defining DerivedCRSs
shall be the same as can be XML encoded in the GML 3.1.1 simple dictionary profile:<?xml version="1.0" encoding="UTF-8"?><Dictionary xmlns="http://www.opengis.net/gml"
xmlns:gml="http://www.opengis.net/gml"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.opengis.net/gml
gml\3.1.1\Profiles\SimpleDictionary\1.0.0\gmlSimpleDictionaryProfile.xsd"
gml:id="DerivedCRStypeDictionary"><!-- Primary editor: Arliss Whiteside. Last updated 2006-02-13 --><name>Derived CRS type standard values</name>24

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

OGC 07-092r3<!-- ===================================================== --><dictionaryEntry><Definition gml:id="geodetic"><description>A coordinate reference system based on a geodetic
datum; provides an accurate representation of the geometry ofgeographic features for a large portion of the earth's surface.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">">urn:ogc:def:derivedCRStype:OGC:1.0:geographic</name></Definition></dictionaryEntry><dictionaryEntry><Definition gml:id="vertical"><description>A coordinate reference system used for recordingof heights or depths. Vertical CRSs make use of the direction ofgravity to define the concept of height or depth, but the relationshipwith gravity may not be straightforward. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:derivedCRStype:OGC:1.0:vertical</name></Definition></dictionaryEntry><dictionaryEntry><Definition gml:id="engineering"><description>A contextually local coordinate reference system;
which can be divided into two broad categories:- earth-fixed systems applied to engineering activities on or near thesurface of the earth;- CRSs on moving platforms such as road vehicles, vessels, aircraft, or
spacecraft. </description><namecodeSpace="urn:ogc:def:derivedCRStype:OGC:OGC:1.0:">engineering</name></Definition></dictionaryEntry><dictionaryEntry><Definition gml:id="image"><description>A derived CRS used like an engineering coordinate
reference system applied to locations in images. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:derivedCRStype:OGC:1.0:image</name></Definition></dictionaryEntry><dictionaryEntry><Definition gml:id="temporal"><description>A reference system used for the recording oftime. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:derivedCRStype:OGC:1.0:temporal</name></Definition></dictionaryEntry></Dictionary>

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OGC 07-092r3

A.3

Definitions of verticalDatumType values

The definitions of the verticalDatumType standard values used in defining
VerticalDatums shall be the same as can be XML encoded in the GML 3.1.1 simple
dictionary profile:<?xml version="1.0" encoding="UTF-8"?><Dictionary xmlns="http://www.opengis.net/gml"
xmlns:gml="http://www.opengis.net/gml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.opengis.net/gml
gml\3.1.1\Profiles\SimpleDictionary\1.0.0\gmlSimpleDictionaryProfile.xsd"
gml:id="VerticalDatumType"><!-- Primary editor: Arliss Whiteside. Last updated 2006-02-13 --><name>Vertical Datum Type standard values</name><!-- ===================================================== --><dictionaryEntry><Definition gml:id="geoidal"><description>The zero value of the associated verticalcoordinate system axis is defined to approximate a constant potential
surface, usually the geoid. Such a reference surface is usually
determined by a national or scientific authority, and is then a wellknown, named datum. </description><name codeSpace="urn:ogc:tc:urn:docbpp:06023">urn:ogc:def:pixelInCell:OGC:1.0:geoidal</name></Definition></dictionaryEntry><dictionaryEntry><!-- ===================================================== --><Definition gml:id="depth"><description>The zero point of the vertical axis is defined bya surface that has meaning for the purpose which the associatedvertical measurements are used for. For hydrographic charts, this isoften a predicted nominal sea surface (i.e., without waves or otherwind and current effects) that occurs at low tide. </description><name codeSpace="urn:ogc:tc:urn:docbpp:06023">urn:ogc:def:pixelInCell:OGC:1.0:depth</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="barometric"><description>Atmospheric pressure is the basis for thedefinition of the origin of the associated vertical coordinate systemaxis. </description><name codeSpace="urn:ogc:tc:urn:docbpp:06023">urn:ogc:def:pixelInCell:OGC:1.0:barometric</name></Definition></dictionaryEntry><dictionaryEntry><!-- ===================================================== --><Definition gml:id="otherSurface"><description>In some cases, e.g. oil exploration andproduction, a geological feature, such as the top or bottom of ageologically identifiable and meaningful subsurface layer, is used as a

26

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OGC 07-092r3
vertical datum. Other variations to the above three vertical datum
types may exist and are all included in this type. </description><name codeSpace="urn:ogc:tc:urn:docbpp:06023">urn:ogc:def:pixelInCell:OGC:1.0:otherSurface</name></Definition></dictionaryEntry></Dictionary>

A.4

Definitions of pixelInCell values

The definitions of the pixelInCell standard values used in defining ImageDatums shall be
the same as can be XML encoded in the GML 3.1.1 simple dictionary profile:<?xml version="1.0" encoding="UTF-8"?><Dictionary xmlns="http://www.opengis.net/gml"
xmlns:gml="http://www.opengis.net/gml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.opengis.net/gml
gml\3.1.1\Profiles\SimpleDictionary\1.0.0\gmlSimpleDictionaryProfile.xsd"
gml:id="PixelInCellDictionary"><!-- Primary editor: Arliss Whiteside. Last updated 2006-02-13 --><name>PixelInCell standard values</name><!-- ===================================================== --><dictionaryEntry><Definition gml:id="cellCenter"><description>The origin of the image coordinate system is at
the centre of a grid cell or image pixel. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:pixelInCell:OGC:1.0:cellCenter</name></Definition></dictionaryEntry><dictionaryEntry><!-- ===================================================== --><Definition gml:id="cellCorner"><description>The origin of the image coordinate system is at
the corner of a grid cell, or half-way between the centres of adjacentimage pixels. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:pixelInCell:OGC:1.0:cellCorner</name></Definition></dictionaryEntry></Dictionary>

A.5

Definitions of rangeMeaning values

The definitions of the rangeMeaning standard values used in defining CoordinateAxes
shall be the same as can be XML encoded in the GML 3.1.1 simple dictionary profile:<?xml version="1.0" encoding="UTF-8"?><Dictionary xmlns="http://www.opengis.net/gml"
xmlns:gml="http://www.opengis.net/gml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

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OGC 07-092r3
xsi:schemaLocation="http://www.opengis.net/gml
gml\3.1.1\Profiles\SimpleDictionary\1.0.0\gmlSimpleDictionaryProfile.xsd"
gml:id="RangeMeaningDictionary"><!-- Primary editor: Arliss Whiteside. Last updated 2006-02-13 --><name>Range Meaning standard values</name><!-- ===================================================== --><dictionaryEntry><Definition gml:id="exact"><description>Any value between and including minimumValue andmaximiumValue is valid. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:rangeMeaning:OGC:1.0:exact</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="wraparound"><description>The axis is continuous with values wrapping
around at the minimumValue and maximumValue. Values with the same
meaning repeat modulo the difference between maximumValue andminimumValue. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:rangeMeaning:OGC:1.0:wraparound</name></Definition></dictionaryEntry></Dictionary>

A.6

Definitions of axisDirection values

The definitions of the axisDirection standard values used in defining CoordinateAxes
shall be the same as can be XML encoded in the GML 3.1.1 simple dictionary profile:<?xml version="1.0" encoding="UTF-8"?><Dictionary xmlns="http://www.opengis.net/gml"
xmlns:gml="http://www.opengis.net/gml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.opengis.net/gml
gml\3.1.1\Profiles\SimpleDictionary\1.0.0\gmlSimpleDictionaryProfile.xsd"
gml:id="AxisDirectionDictionary"><!-- Primary editor: Arliss Whiteside. Last updated 2006-02-13 --><name>Axis Direction standard values</name><!-- ===================================================== --><dictionaryEntry><Definition gml:id="north"><description>Axis positive direction is north. In a geographic
or projected CRS, north is defined through the geodetic datum. In an
engineering CRS, north may be defined with respect to an engineering
object rather than a geographical direction. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:north</name></Definition></dictionaryEntry><!-- ===================================================== -->28

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

OGC 07-092r3<dictionaryEntry><Definition gml:id="northNorthEast"><description>Axis positive direction is approximately northnorth-east. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:northNorthEast</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="northEast"><description>Axis positive direction is approximately northeast. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:northEast</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="eastNorthEast"><description>Axis positive direction is approximately eastnorth-east. </description><name codeSpace="urn:ogc:tc:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:eastNorthEast</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="east"><description>Axis positive direction is pi/2 radians clockwisefrom north. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:east</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="eastSouthEast"><description>Axis positive direction is approximately eastsouth-east. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:eastSouthEast</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="southEast"><description>Axis positive direction is approximately southeast.</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:southEast</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="southSouthEast">

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29

OGC 07-092r3<description>Axis positive direction is approximately southsouth-east. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:southSouthEast</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="south"><description>Axis positive direction is pi radians clockwisefrom north. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:south</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="southSouthWest"><description>Axis positive direction is approximately southsouth-west. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:southSouthWest</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="southWest"><description>Axis positive direction is approximately southwest. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:southWest</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="westSouthWest"><description>Axis positive direction is approximately westsouth-west. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:westSouthWest</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="west"><description>Axis positive direction is 3pi/2 radiansclockwise from north. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:west</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="westNorthWest"><description>Axis positive direction is approximately westnorth-west. </description>

30

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

OGC 07-092r3<name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:westNorthWest</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="northWest"><description>Axis positive direction is approximately northwest.</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:northWest</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="northNorthWest"><description>Axis positive direction is approximately northnorth-west. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:northNorthWest</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="up"><description>Axis positive direction is up relative togravity. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:up</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="down"><description>Axis positive direction is down relative togravity. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:down</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="geocentricX"><description>Axis positive direction is in the equatorial
plane from the centre of the modelled earth towards the intersection of
the equator with the prime meridian. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:geocentricX</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="geocentricY"><description>Axis positive direction is in the equatorial
plane from the centre of the modelled earth towards the intersection of

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OGC 07-092r3
the equator and the meridian pi/2 radians eastwards from the prime
meridian. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:geocentricY</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="geocentricZ"><description>Axis positive direction is from the centre of themodelled earth parallel to its rotation axis and towards its northpole. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:geocentricZ</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="future"><description>Axis positive direction is towards the future.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:future</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="past"><description>Axis positive direction is towards the past.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:past</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="columnPositive"><description>Axis positive direction is towards higher column
numbers. </description><name codeSpace="urn:ogc:tc:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:columnNegative</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="columnNegative"><description>Axis positive direction is towards lower pixel
column numbers. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:columnNegative</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="rowPositive"><description>Axis positive direction is towards higher row
numbers. </description>

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OGC 07-092r3<namecodeSpace="urn:opengis:def:axisDirection:1.0:">rowPositive</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="rowNegative"><description>Axis positive direction is towards lower pixel
row numbers. </description><name codeSpace="urn:opengis:def:axisDirection:OGC:1.0:"/></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="displayRight"><description>Axis positive direction is right in display.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:displayRight</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="displayLeft"><description>Axis positive direction is left in display.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:displayLeft</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="displayUp"><description>Axis positive direction is towards top of
approximately vertical display surface.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:displayUp</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="displayDown"><description>Axis positive direction is towards bottom ofapproximately vertical display surface.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:opengis:def:axisDirection:OGC:1.0:displayDown</name></Definition></dictionaryEntry></Dictionary>

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OGC 07-092r3

A.7

Definitions of units-of-measure

The definitions of the some commonly used unit-of-measure (uom) values shall be thesame as can be XML encoded in the GML 3.1.1 dictionary:<?xml version="1.0" encoding="UTF-8"?><Dictionary xmlns="http://www.opengis.net/gml"
xmlns:gml="http://www.opengis.net/gml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xlink="http://www.w3.org/1999/xlink"
xsi:schemaLocation="http://www.opengis.net/gml
gml/3.1.1/base/coordinateReferenceSystems.xsd"
gml:id="UnitsDictionary"><!-- Primary editor: Arliss Whiteside. Last updated 2006-02-13 --><description>Example GML Dictinary of unit
definitions.</description><name>Units Dictionary</name><dictionaryEntry><ConventionalUnit gml:id="degree"><name>degree</name><name codeSpace="urn:ogc:def:parameter:EPSG::">9102</name><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:uom:OGC:1.0:degree</name><quantityType>angle</quantityType><conversionToPreferredUnit uom="#radian"><factor>1.74532925199433E-02</factor></conversionToPreferredUnit></ConventionalUnit></dictionaryEntry><dictionaryEntry><BaseUnit gml:id="radian"><name>radian</name><quantityType>angle</quantityType><unitsSystem xlink:href="urn:ogc:ToBeSupplied"/></BaseUnit></dictionaryEntry><dictionaryEntry><BaseUnit gml:id="metre"><name>metre</name><name codeSpace="urn:ogc:def:parameter:EPSG::">9001</name><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:uom:OGC:1.0:metre</name><quantityType>length</quantityType><unitsSystem xlink:href="urn:ogc:SI"/></BaseUnit></dictionaryEntry><dictionaryEntry><BaseUnit gml:id="unity"><name>unity</name><name codeSpace="urn:ogc:def:uom:EPSG::">8805</name><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:uom:OGC:1.0:unity</name><quantityType>scale factor</quantityType><unitsSystem xlink:href="urn:ogc:ToBeSupplied"/></BaseUnit></dictionaryEntry>

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Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

OGC 07-092r3</Dictionary>

A.8

Definitions of data types

The definitions of the some commonly used data types shall be the same as can be XML
encoded in the GML 3.1.1 simple dictionary profile:<?xml version="1.0" encoding="UTF-8"?><Dictionary xmlns="http://www.opengis.net/gml"
xmlns:gml="http://www.opengis.net/gml"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.opengis.net/gml
gml\3.1.1\Profiles\SimpleDictionary\1.0.0\gmlSimpleDictionaryProfile.xsd"
gml:id="parameterTypeDictionary"><!-- Primary editor: Arliss Whiteside. Last updated 2006-02-13 --><name>dataType URN standard values</name><name>Data type of a quantity. Usually refers to a data type definedin measures.xsd or allowed in the ParameterValueType of
coordinateOperations.xsd. </name><!-- ===================================================== --><dictionaryEntry><Definition gml:id="measure"><description>General numeric value of a quantity, with its
associated unit of measure. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:measure</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="length"><description>Value of a length (or distance) quantity, with
its units. Uses the MeasureType with the restriction that the unit ofmeasure referenced by uom must be suitable for a length, such as metresor feet. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:length</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="scale"><description>Value of a scale factor (or ratio) that has no
physical unit. Uses the MeasureType with the restriction that the unitof measure referenced by uom must be suitable for a scale factor, suchas one, percent, permil, or parts-per-million. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:scale</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="time">

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

35

OGC 07-092r3<description>Value of a time or temporal quantity, with its
units. Uses the MeasureType with the restriction that the unit ofmeasure referenced by uom must be suitable for a time value, such as
seconds or weeks. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:time</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="gridLength"><description>Value of a length (or distance) quantity in agrid, where the grid spacing does not have any associated physicalunits, or does not have a constant physical spacing. This grid length
will often be used in a digital image grid, where the base units arelikely to be pixel spacings. Uses the MeasureType with the restrictionthat the unit of measure referenced by uom must be suitable for length
along the axes of a grid, such as pixel spacings or grid
spacings.</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:gridLength</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="angle"><description>Value of an angle quantity, with its units. Uses
the MeasureType with the restriction that the unit of measurereferenced by uom must be suitable for an angle, such as degrees orradians. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:angle</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="lengthOrAngle"><description>Value of a length or angle quantity, where anangle can be recorded in either degree-minute-second format or single
value format. Often used for horizontal ground coordinates.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:lengthOrAngle</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="string"><description>String value of a quantity. A string value does
not have an associated unit of measure. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:string</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="positiveInteger">

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Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

OGC 07-092r3<description>Positive integer value of a quantity, usuallyused for a count. An integer value does not have an associated unit ofmeasure. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:positiveInteger</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="nonNegativeInteger"><description>Zero or positive integer value of a quantity. An
integer value does not have an associated unit of measure.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:nonNegativeInteger</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="boolean"><description>Boolean value of a quantity. A Boolean value does
not have an associated unit of measure. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:boolean</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="measureList"><description>Ordered sequence of two or more numeric values ofa quantity list, where each value has the same associated unit ofmeasure. An element of this type contains a space-separated list of
double values. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:measureList</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="lengthList"><description>Ordered sequence of two or more numeric values ofa list of Length measures. Each value has the same associated unit ofmeasure suitable for a length, such as metres or feet. An element of
this type contains a space-separated list of double values.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:lengthList</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="scaleList"><description>Ordered sequence of two or more numeric values ofa list of Scale measures. Each value has the same associated unit ofmeasure suitable for a scale factor, such as one, percent, permil, orparts-per-million. An element of this type contains a space-separated
list of double values. </description>

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

37

OGC 07-092r3<name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:scaleList</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="angleList"><description>Ordered sequence of two or more numeric values ofa list of Angle measures. Each value has the same associated unit ofmeasure suitable for an angle, such as degrees or radians. An elementof this type contains a space-separated list of double values.
</description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:angleList</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="timeList"><description>Ordered sequence of two or more numeric values ofa list of Time measures, each recorded as a single number. Each value
has the same associated unit of measure suitable for a time value, suchas seconds or days. An element of this type contains a space-separated
list of double values. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:timeList</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="gridLengthList"><description>Ordered sequence of two or more Grid Length
measures. Each value has the same associated unit of measure suitable
for length along the axes of a grid, such as pixel spacings or grid
spacings. An element of this type contains a space-separated list of
double values. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:gridLengthList</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="integerList"><description>Ordered sequence of two or more integer values,
usually used for counts. These integer values do not have an associatedunit of measure. An element of this type contains a space-separated
list of integer values. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:integerList</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="positiveIntegerList"><description>Ordered sequence of two or more positive integer
values, usually used for counts. These integer values do not have an

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Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

OGC 07-092r3
associated unit of measure. An element of this type contains a spaceseparated list of integer values. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:positiveIntegerList</name></Definition></dictionaryEntry><!-- ===================================================== --><dictionaryEntry><Definition gml:id="anyURI"><description>Reference to a file or a part of a filecontaining one or more parameter values, each numeric value with its
associated unit of measure. When referencing a part of a file, thatfile must contain multiple identified parts, such as an XML encoded
document. Furthermore, the referenced file or part of a file canreference another part of the same or different files, as allowed in
XML documents. </description><name codeSpace="urn:ogc:tc:urn:doc:bpp:06023">urn:ogc:def:dataType:OGC:1.1:anyURI</name></Definition></dictionaryEntry></Dictionary>

Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.

39

OGC 07-092r3

Bibliography[1]

OGC 02-058, Web Feature Service Implementation Standard, v1.0.0[2]

OGC 03-065r6, Web Coverage Service Implementation Standard, v1.0.0[3]

OGC 05-013, Web Coordinate Transformation Service Implementation Standard,
draft

[4]

OGC 05-060, URNs 05-010 change request – Specify data type URNs

[5]

OGC 05-091r2, Add additional objectTypes and authorities to the OGC “def” URN
scheme[6]

OGC 05-095r1, GML 3.1.1 common CRSs profile[7]

OGC 07-092, Corrigendum 2 for OpenGIS Best Practices Paper 06-023r1[8]

ISO 31:1992, Quantities and Units. (13 Parts, with revisions 1998)[9]

XML Schema: Component Designators, W3C Working Draft 29 March 2005

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Copyright © 2009 Open Geospatial Consortium, Inc. All Rights Reserved.