EPSG:9659

Method

Geographic3D to 2D conversion

Attributes

Data source: OGP

Information source: EPSG guidance note #7-2, http://www.epsg.org

Revision date: 2015-05-22

Remarks: This is a parameter-less conversion.

Export

Definition: OGP XML

<?xml version="1.0" encoding="UTF-8"?>
 <gml:OperationMethod xmlns:epsg="urn:x-ogp:spec:schema-xsd:EPSG:1.0:dataset" xmlns:gml="http://www.opengis.net/gml/3.2" xmlns:xlink="http://www.w3.org/1999/xlink" gml:id="iogp-method-9659">
  <gml:metaDataProperty>
    <epsg:CommonMetaData>
      <epsg:informationSource>EPSG guidance note #7-2, http://www.epsg.org</epsg:informationSource>
      <epsg:revisionDate>2015-05-22</epsg:revisionDate>
      <epsg:changes>
        <epsg:changeID xlink:href="urn:ogc:def:change-request:EPSG::2015.018" />
      </epsg:changes>
      <epsg:show>true</epsg:show>
      <epsg:isDeprecated>false</epsg:isDeprecated>
    </epsg:CommonMetaData>
  </gml:metaDataProperty>
  <gml:metaDataProperty>
    <epsg:CoordinateOperationMethodMetaData>
      <epsg:isOperationReversible>true</epsg:isOperationReversible>
      <epsg:example>(none)</epsg:example>
    </epsg:CoordinateOperationMethodMetaData>
  </gml:metaDataProperty>
  <gml:identifier codeSpace="IOGP">urn:ogc:def:method:EPSG::9659</gml:identifier>
  <gml:name>Geographic3D to 2D conversion</gml:name>
  <gml:remarks>This is a parameter-less conversion.</gml:remarks>
  <gml:formula>Note: These formulas have been transcribed from EPSG Guidance Note #7-2. Users are encouraged to use that document rather than the text which follows as reference because limitations in the transcription will be avoided.

The forward case is trivial. A 3-dimensional geographic coordinate reference system comprising of geodetic latitude, geodetic longitude and ellipsoidal height is converted to its 2-dimensional subset by the simple expedient of dropping the height. The axis order change operates on coordinates of a point whose order change is described by the following matrix operation:

[Derived CRS 1st coordinate]   [1  0  0]   [Base CRS 1st coordinate]
[Derived CRS 2nd coordinate] = [0  1  0] * [Base CRS 2nd coordinate]
[Derived CRS 3rd coordinate]   [0  0  0]   [Base CRS 3rd coordinate]


The reverse conversion, from 2D to 3D, is indeterminate. It is however a requirement when a geographic 2D coordinate reference system is to be transformed using a geocentric method which is 3-dimensional. In practice an artificial ellipsoidal height is created and appended to the geographic 2D coordinate reference system to create a geographic 3D coordinate reference system referenced to the same geodetic datum. The assumed ellipsoidal height is usually either set to the gravity-related height of a position in a compound coordinate reference system, or set to zero. As long as the height chosen is within a few kilometres of sea level, no error will be induced into the horizontal position resulting from the later geocentric transformation; the vertical coordinate will however be meaningless.</gml:formula>
</gml:OperationMethod>
<?xml version="1.0" encoding="UTF-8"?>
 <gml:OperationMethod xmlns:epsg="urn:x-ogp:spec:schema-xsd:EPSG:1.0:dataset" xmlns:gml="http://www.opengis.net/gml/3.2" xmlns:xlink="http://www.w3.org/1999/xlink" gml:id="iogp-method-9659">
  <gml:metaDataProperty>
    <epsg:CommonMetaData>
      <epsg:informationSource>EPSG guidance note #7-2, http://www.epsg.org</epsg:informationSource>
      <epsg:revisionDate>2015-05-22</epsg:revisionDate>
      <epsg:changes>
        <epsg:changeID xlink:href="urn:ogc:def:change-request:EPSG::2015.018" />
      </epsg:changes>
      <epsg:show>true</epsg:show>
      <epsg:isDeprecated>false</epsg:isDeprecated>
    </epsg:CommonMetaData>
  </gml:metaDataProperty>
  <gml:metaDataProperty>
    <epsg:CoordinateOperationMethodMetaData>
      <epsg:isOperationReversible>true</epsg:isOperationReversible>
      <epsg:example>(none)</epsg:example>
    </epsg:CoordinateOperationMethodMetaData>
  </gml:metaDataProperty>
  <gml:identifier codeSpace="IOGP">urn:ogc:def:method:EPSG::9659</gml:identifier>
  <gml:name>Geographic3D to 2D conversion</gml:name>
  <gml:remarks>This is a parameter-less conversion.</gml:remarks>
  <gml:formula>Note: These formulas have been transcribed from EPSG Guidance Note #7-2. Users are encouraged to use that document rather than the text which follows as reference because limitations in the transcription will be avoided.

The forward case is trivial. A 3-dimensional geographic coordinate reference system comprising of geodetic latitude, geodetic longitude and ellipsoidal height is converted to its 2-dimensional subset by the simple expedient of dropping the height. The axis order change operates on coordinates of a point whose order change is described by the following matrix operation:

[Derived CRS 1st coordinate]   [1  0  0]   [Base CRS 1st coordinate]
[Derived CRS 2nd coordinate] = [0  1  0] * [Base CRS 2nd coordinate]
[Derived CRS 3rd coordinate]   [0  0  0]   [Base CRS 3rd coordinate]


The reverse conversion, from 2D to 3D, is indeterminate. It is however a requirement when a geographic 2D coordinate reference system is to be transformed using a geocentric method which is 3-dimensional. In practice an artificial ellipsoidal height is created and appended to the geographic 2D coordinate reference system to create a geographic 3D coordinate reference system referenced to the same geodetic datum. The assumed ellipsoidal height is usually either set to the gravity-related height of a position in a compound coordinate reference system, or set to zero. As long as the height chosen is within a few kilometres of sea level, no error will be induced into the horizontal position resulting from the later geocentric transformation; the vertical coordinate will however be meaningless.</gml:formula>
</gml:OperationMethod>