09-108b Grid CRS URNs

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Open Geospatial Consortium

Document OGC 09-108

CR-Form-v3

CHANGE REQUEST



_{OGC URNs for}

definitions

CR ?

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Proposed change affects:  AS Imp Spec Best Practices Paper Other X

Title:  OGN URN change request: Add grid CRS URNs

Source:  Arliss Whiteside and other WCS SWG members

Work item code:  Date:  2009-09-09

Category:  B (Addition of feature)

Use one of the following categories:

F (Critical correction)

A (corresponds to a correction in an earlier release)

B (Addition of feature),

C (Functional modification of feature)

D (Editorial modification)

Reason for change:  URNs in the “ogc” URN namespace are often effective and efficient for

referencing the definitions of CRSs and their components. A set of these URNs for ImageCRSs was thus specified in Clause 10 of approved

Implementation Specification OGC 05-096r1 “GML 3.1.1 grid CRSs profile”. However, those URNs have not yet been accepted by the more-recently-formed OGC Naming Authority.

Summary of change:  Add definitions of eight URNs for definitions of ImageCRSs and their

components, to the registry of URNs approved by the OGC Naming Authority

Consequences if 

not approved:

Failure to allow previously specified URNs for ImageCRSs and their components, some of which are being used with WCS 1.1.

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Other specs  X Other core specifications  WCS 1.1, GML 3.1.1 grid CRSs profile

Affected: Abstract specifications

Best Practices Papers

Supporting Doc. 

Other comments: 

Status 

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Page

1 Introduction...2

2 2D Grid coordinate system...3

3 Row coordinate axis...4

4 Column coordinate axis...5

5 Grid spacing unit of measure...5

6 Image CRSs with origin in centre of first pixel...6

7 Image CRSs with origin in corner of first pixel...8

8 Image datum at pixel centre...9

9 Image datum at pixel corner...10

1 Introduction

This change request specifies a standard set of definitions and corresponding URNs that

may be used whenever applicable for unrectified images and other grid coverages. Most

of these definitions are encoded using the GML 3.1.1 Grid CRSs profile specified in

(approved Implementation Specification) OGC 05-096r1.

This change request removes Clause 10 from OGC 05-096r1, in which all of these URNs

were previously specified, and modifies that material for:

a) Corrigenda OGC 06-111 and 06-146 to OGC 05-096r1

b) Comply with recently revised policy document OGC 06-135r7

c) Correct “first pixel” to “corner pixel in the image file with the lowest pixel indices as

defined by that file format”

d) R

everse the order of "row" and "column"

axes in a grid CS

e) Specify that

the "column" axis

is

first axis defined by the

image-recording

format,

and

the

"row"

axis is

the second axis

defined

.

f) More clearly state recommendations for use of these URNs.

These requested URNs are defined for use when it is more effective or efficient to

reference definitions of ImageCRSs and their components using URNs, instead of using

URLs. As specified in Clause 10.3.2 of OWS Common 1.1 (OGC 06-121r3), when a

URL is used to reference a definition:

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Standard URNs for unrectified image CRSs

URN Object name & gml:id Definition

specified in

urn:ogc:def:cs:OGC:0.0:GridCS2d GridCS2d Clause 2

urn:ogc:def:axis:OGC:0.0:Row Row Clause 3

urn:ogc:def:axis:OGC:0.0:Column Column Clause 4

urn:ogc:def:uom:OGC:0.0:GridSpacing GridSpacing Clause 5

urn:ogc:def:crs:OGC:0.0: ImageCRSpixelCenter:TBD a ImageCRSpixelCenterTBD Clause 6 urn:ogc:def:crs:OGC:0.0:ImageCRSpixelCorner:TBD a ImageCRSpixelCornerTBD Clause 7 urn:ogc:def:datum:OGC:0.0:ImageDatumPixelCenter:TBD a ImageDatumPixelCenterTBD Clause 8 urn:ogc:def:datum:OGC:0.0:ImageDatumPixelCorner:TBD a ImageDatumPixelCornerTBD Clause 9 a This “TBD” shall be replaced by the image identifier alphanumeric character string. These image identifier alphanumeric character string shall be unique.

The first four of these URNs use the format for single objects specified in Subclause 7.1

of “URNs of definitions in ogc namespace” [OGC 07-092r3].The other four of these

URNs use the format for not-completely-specified objects specified in Subclause 7.2 of

[OGC 07-092r3]. These not-completely-specified objects are used because each original

image must have a different ImageCRS and ImageDatum.

NOTE In general, there may b e a very large number of different original images. As stated in Clause 5.2.7 of Discussion Paper OGC 04-052, a large enterprise may archive on the order of 10,000,000 different images, and receive on the order of 10,000 new images per day!

2 2D Grid coordinate system

The URN “urn:ogc:def:cs:OGC:0.0:GridCS2d”

shall reference the definition of a

Coordinate System for a 2D rectangular grid of grid points. The definition of this grid

coordinate system shall be the same as can be XML encoded using GML 3.1.1 as:

<?xml version="1.0" encoding="UTF-8"?>

<CartesianCS 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 http://schemas.opengis.net/gml/3.1.1/base/gml.xsd"

gml:id="GridCS2d">

<csName>2D grid coordinate system</csName>

<csID>

<name codeSpace="urn:ogc:def:cs:OGC:1.0:">GridCS2d</name> </csID>

<remarks>A 2D grid coordinate system for use by an image or other

grid coverage. It can be used for a grid of any size, since no grid size is defined. This coordinate system specifies that each "column"

coordinate value will be listed before the "row" coordinate value. The grid points are assumed to have the same "grid spacing" in each

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The first "column" axis shall correspond to the pixel index listed first in the file format definition, and the second "row" axis shall

correspond to the pixel index listed second. This relationship between the "column and "row" names and the grid point indices shall apply whether this GridCS2d is associated with a grid file before or after that file is recorded.

The "column" and "row" axis names are used here although other axis names may be used by the file format definition, or by the

"scanDirection : Sequence(CharacterString)" attribute of the CV_Grid class defined in Clause 8 of ISO 19123. Use of other axis names would require defining different CartesianCSs for other names, or adding other names as additional axisID values. The XML definitions of the Row and Column axes includes the alternative axis names "line" and "sample" as additional axisID values.

(The first row in a grid is sometimes called the "top" row, the first column is sometimes called the "left" column, and the lowest indices grid point is then called the "upperLeft" point. However other names can also be used, since this GridCS2d is defined so that it does not depend on such left/right, top/bottom, and up/down names.) </remarks>

This xml document references the two standard grid axes specified below.

3 Row coordinate axis

The URN “urn:ogc:def:axis:OGC:0.0:Row”

shall reference the definition of the row

coordinate axis for a 2D grid coordinate system. The definition of this row axis shall be

the same as can be XML encoded using GML 3.1.1 as:

<CoordinateSystemAxis xmlns="http://www.opengis.net/gml"

gml:id="Column" gml:uom="urn:ogc:def:uom:OGC:1.0:GridSpacing">

<name>Grid column axis</name>

<name codeSpace="urn:ogc:def:axis:OGC:1.0:">Column</name> </axisID>

<name codeSpace="urn:ogc:def:axis:OGC:1.0:">Sample</name> </axisID>

<remarks>For this first "column" grid axis, column coordinate values match grid column numbers, but allow fractional coordinate values

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column, so the direction of this axis is "right", but these terms are not required. </remarks>

<axisDirection>urn:ogc:def:axisDirection:OGC:1.0:columnPositive</axisDir ection>

</CoordinateSystemAxis>

4 Column coordinate axis

The URN “urn:ogc:def:axis:OGC:0.0:Column”

shall reference the definition of the

column coordinate axis for a 2D grid coordinate system. The definition of this column

axis shall be the same as can be XML encoded using GML 3.1.1 as:

<CoordinateSystemAxis xmlns="http://www.opengis.net/gml"

gml:id="Row" gml:uom="urn:ogc:def:uom:OGC:1.0:GridSpacing">

<name>Grid row axis</name>

<remarks>For this second "Row" grid axis, row coordinate values match grid row numbers, but allow fractional coordinate values between grid points. The first row in a grid is sometimes called the "top" row, so the direction of this axis is "down", but these terms are not required.

</remarks>

<axisDirection>urn:ogc:def:axisDirection:OGC:1.0:rowPositive</axisDirect ion>

</CoordinateSystemAxis>

5 Grid spacing unit of measure

The URN “urn:ogc:def:uom:OGC:0.0:GridSpacing”

shall reference the definition of the

grid spacing unit of measure (uom). The definition of this unit shall be the same as can be

XML encoded using GML 3.1.1 as:

<BaseUnit xmlns="http://www.opengis.net/gml"

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gml:id="GridSpacing">

<!-- This GridSpacing unit of measure (UOM) is defined, and

recommended, for use when it is more effective to reference this UOM definition using a URN. For referencing this UOM definition using a URL, another or a modified definition is needed. -->

<name>Spacing between adjacent grid lines, or between centers of adjacent pixels</name>

<name codeSpace="urn:ogc:def:uom:OGC:1.0:">GridSpacing</name> <quantityType>Length</quantityType>

6 Image CRSs with origin in centre of first pixel

The URN value “urn:ogc:def:crs:OGC:0.0:ImageCRSpixelCenter:TBD”

shall reference

the definition of an (unrectified) image CRS with its origin in the centre of the corner

pixel in the image file with the lowest pixel indices as defined by that file format. This

image CRS shall be for the specific image whose alphanumeric character string identifier

is substituted for the “TBD” in this URN.

NOTE 1 This document does not specify any format for an image alphanumeric identifier, since many different formats are used for such identifiers. However, these image alphanumeric identifiers must be unique. One such format could concatenate a camera identifier with the image collection date and time.

The definitions of these image CRSs shall be the same as can be XML encoded using

GML 3.1.1 as:

<ImageCRS xmlns="http://www.opengis.net/gml"

gml:id="ImageCRSpixelCenterTBD">

<!-- This set of image CRSs is defined, and recommended, for use under two conditions:

1) When it is more effective to reference an image CRS definition using a URN, instead of a URL.

For referencing an image CRS definition using a URL, other or modified definitions are needed.

2) When the image is recorded in any one of the (unspecified) set of specific image formats for which these image CRSs are well-defined and appropriate.

For an image recorded in any other format, other image CRS definitions should be used. -->

<srsName>Image TBD CRS pixel centers</srsName>

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<srsID> <name

codeSpace="urn:ogc:def:crs:OGC:1.0:ImageCRSpixelCenter:">TBD</name>

</srsID>

<remarks>Parameterized definition of 2D image coordinate reference

systems with the origin at the center of the corner pixel in the image file with the lowest pixel indices as defined by that file format. This CRS definition can be used for any size image, since no image size is specified.

This CRS definition is designed to be used for ungeorectified images, and is not expected to be used for a georectified image. This definition can be used for a georeferenced or ungeoreferenced image, where a

georeferenced image CRS is associated with the coordinate Transformation(s) that georeference it. </remarks>

<usesCartesianCS xlink:href="urn:ogc:def:cs:OGC:1.0:GridCS2d"/> <usesImageDatum

xlink:href="urn:ogc:def:datum:OGC:1.0:ImageDatumPixelCenter:TBD"/> </ImageCRS>

NOTE 2 It is not expected to be necessary in most cases to produce an XML document that specifies the image CRS for a specific image identifier, since this CRS definition can be referenced using the specified URN value with the “TBD” replaced by the specific image identifier. However, it is possible to do this, as shown in the following example.

EXAMPLE If this XML document were modified to specify the image CRS with its origin in the centre of first pixel for an image with the identifier “C543D041201T084027”, this XML document could be:

<ImageCRS xmlns="http://www.opengis.net/gml" xmlns:gml="http://www.opengis.net/gml"

<srsName>Image C543D041201T084027 CRS pixel centers</srsName> <srsID>

<name

codeSpace="urn:ogc:def:crs:OGC:1.0:ImageCRSpixelCenter:">C543D041201T084027</nam e>

</srsID>

xlink:href="urn:ogc:def:datum:OGC:1.0:ImageDatumPixelCenter:C543D041201T084027"/ >

</ImageCRS>

7 Image CRSs with origin in corner of first pixel

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The definitions of these image CRSs shall be the same as can be XML encoded using

GML 3.1.1 as:

<ImageCRS xmlns="http://www.opengis.net/gml"

<!-- This set of image CRSs is defined, and recommended, for use under two conditions:

1) When it is more effective to reference an image CRS definition using a URN, instead of a URL.

For referencing an image CRS definition using a URL, other or modified definitions are needed.

2) When the image is recorded in any one of the (unspecified) set of specific image formats for which these image CRSs are well-defined and appropriate.

For an image recorded in any other format, other image CRS definitions should be used. -->

<srsName>Image TBD CRS pixel corners</srsName>

<srsID> <name

codeSpace="urn:ogc:def:crs:OGC:1.0:ImageCRSpixelCorner:">TBD</name>

</srsID>

<remarks>Parameterized definition of 2D image coordinate reference

systems with the origin at the outside corner of the corner pixel in the image file with the lowest pixel indices as defined by that file format. This CRS definition can be used for any size image, since no image size is specified.

This CRS definition is designed to be used for ungeorectified images, and is not expected to be used for a georectified image. This definition can be used for a georeferenced or ungeoreferenced image, where a

georeferenced image CRS is associated with the coordinate Transformation(s) that georeference it. </remarks>

xlink:href="urn:ogc:def:datum:OGC:1.0:ImageDatumPixelCorner:TBD"/> </ImageCRS>

EXAMPLE If this XML document were modified to specify the image CRS with its origin in the outside corner of first pixel for an image with the identifier “C543D041201T084027”, this XML document could be:

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<srsName>Image C543D041201T084027 CRS pixel corners</srsName> <srsID>

<name

codeSpace="urn:ogc:def:crs:OGC:1.0:ImageCRSpixelCorner:">C543D041201T084027</nam e>

</srsID>

xlink:href="urn:ogc:def:datum:OGC:1.0:ImageDatumPixelCorner:C543D041201T084027"/ >

</ImageCRS>

8 Image datum at pixel centre

The URN “urn:ogc:def:datum:OGC:0.0:ImageDatumPixelCenter:TBD”

shall reference

the definition of an image datum with its origin in the centre of the corner pixel in the

image file with the lowest pixel indices as defined by that file format. This image datum

shall be for the specific image whose alphanumeric character string identifier is

substituted for the “TBD” in this URN. The definition of this image datum shall be the

same as can be XML encoded using GML 3.1.1 as:

<ImageDatum xmlns="http://www.opengis.net/gml"

<!-- This set of image datums is defined, and recommended, for use under two conditions:

1) When it is more effective to reference an image datum definition using a URN, instead of a URL.

For referencing an image datum definition using a URL, other or modified definitions are needed.

2) When the image is recorded in any one of the (unspecified) set of specific image formats for which these image datums are well-defined and appropriate.

For an image recorded in any other format, other image datum definitions should be used. -->

<datumName>Image TBD datum with origin at center of first

pixel</datumName> <datumID>

<name

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<remarks>2D image datum with the origin at the center of the corner pixel in the image file with the lowest pixel indices. </remarks>

<anchorPoint>The origin is the center of the corner pixel with the

lowest indices as defined by the image file format. The pixel index listed first in the file format definition is used by the first axis in the coordinate system used with this datum, and the pixel index listed second is used by the first axis in the coordinate system.

</anchorPoint> <pixelInCell

codeSpace="urn:ogc:def:pixelInCell:OGC:1.0:">cellCorner</pixelInCell> </ImageDatum>

9 Image datum at pixel corner

The URN “urn:ogc:def:datum:OGC:0.0:ImageDatumPixelCorner:TBD”

shall reference

the definition of an image datum with its origin at the outside corner of the corner pixel in

the image file with the lowest pixel indices as defined by that file format. This image

datum shall be for the specific image whose alphanumeric character string identifier is

substituted for the “TBD” in this URN. Use of this ImageDatum is discouraged, since it

is not consistent with ISO 19123. The definition of this image datum shall be the same as

can be XML encoded using GML 3.1.1 as:

<ImageDatum xmlns="http://www.opengis.net/gml"

<!-- This set of image datums is defined, and recommended, for use under two conditions:

1) When it is more effective to reference an image datum definition using a URN, instead of a URL.

For referencing an image datum definition using a URL, other or modified definitions are needed.

2) When the image is recorded in any one of the (unspecified) set of specific image formats for which these image datums are well-defined and appropriate.

For an image recorded in any other format, other image datum definitions should be used. -->

<datumName>Image TBD datum with origin at outside corner of first

pixel</datumName> <datumID>

<name

codeSpace="urn:ogc:def:crs:OGC:1.0:ImageDatumPixelCorner:">TBD</name> </datumID>

<remarks>2D image datum with the origin at the outside corner of the

corner pixel in the image file with the lowest pixel indices. </remarks>

<anchorPoint>The origin is the outside corner of the corner pixel

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axis in the coordinate system used with this datum, and the pixel index listed second is used by the first axis in the coordinate system.

</anchorPoint> <pixelInCell

09-108b Grid CRS URNs

Open Geospatial Consortium

Document OGC 09-108

CHANGE REQUEST

OGC URNs for

definitions

CR ?

-

HELP

Contents

Page

1

Introduction...2

2

2D Grid coordinate system...3

3

Row coordinate axis...4

4

Column coordinate axis...5

5

Grid spacing unit of measure...5

6

Image CRSs with origin in centre of first pixel...6

7

Image CRSs with origin in corner of first pixel...8

8

Image datum at pixel centre...9

9

Image datum at pixel corner...10

1

Introduction

This change request specifies a standard set of definitions and corresponding URNs that

may be used whenever applicable for unrectified images and other grid coverages. Most

of these definitions are encoded using the GML 3.1.1 Grid CRSs profile specified in

(approved Implementation Specification) OGC 05-096r1.

This change request removes Clause 10 from OGC 05-096r1, in which all of these URNs

were previously specified, and modifies that material for:

a) Corrigenda OGC 06-111 and 06-146 to OGC 05-096r1

b) Comply with recently revised policy document OGC 06-135r7

c) Correct “first pixel” to “corner pixel in the image file with the lowest pixel indices as

defined by that file format”

d) R

everse the order of "row" and "column"

axes in a grid CS

e) Specify that

the "column" axis

is

first axis defined by the

image-recording

format,

and

the

"row"

axis is

the second axis

defined

.

f) More clearly state recommendations for use of these URNs.

These requested URNs are defined for use when it is more effective or efficient to

reference definitions of ImageCRSs and their components using URNs, instead of using

URLs. As specified in Clause 10.3.2 of OWS Common 1.1 (OGC 06-121r3), when a

URL is used to reference a definition:

Standard URNs for unrectified image CRSs

The first four of these URNs use the format for single objects specified in Subclause 7.1

of “URNs of definitions in ogc namespace” [OGC 07-092r3].The other four of these

URNs use the format for not-completely-specified objects specified in Subclause 7.2 of

[OGC 07-092r3]. These not-completely-specified objects are used because each original

image must have a different ImageCRS and ImageDatum.

2

2D Grid coordinate system

The URN “urn:ogc:def:cs:OGC:0.0:GridCS2d”

shall reference the definition of a

Coordinate System for a 2D rectangular grid of grid points. The definition of this grid

coordinate system shall be the same as can be XML encoded using GML 3.1.1 as:

This xml document references the two standard grid axes specified below.

3

Row coordinate axis

The URN “urn:ogc:def:axis:OGC:0.0:Row”

shall reference the definition of the row

coordinate axis for a 2D grid coordinate system. The definition of this row axis shall be

_{OGC URNs for}

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