Changes between Version 5 and Version 6 of VerticalCS


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Timestamp:
Sep 18, 2012, 6:24:42 AM (7 years ago)
Author:
mloskot
Comment:

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  • VerticalCS

    v5 v6  
    4040 * There does not appear to be a !VerticalUnitSizeGeoKey allowing user defined vertical units similarly to the !ProjLinearSizeGeoKey, so it is not appropriate to use !KvUserDefined for !VerticalUnitsGeoKey.
    4141 * The libgeotiff epsg_vertcs.inc file seems to imply that the vertical datum codes in the range 5000 to 5299 should be considered vertical coordinate systems which they are not in the EPSG data model. It is not clear whether this is something that changed in the EPSG data model after the initiation of the GeoTIFF specification, or if it was an error by the GeoTIFF/libgeotiff authors. This mismatch is why Unknown-5101 above is not reported as Newlyn directly. Spec issue reported at http://trac.osgeo.org/geotiff/ticket/24
    42  * The EPSG and OGC models include an EPSG code for a composite coordinate system. The composite coordinate system is a collection of a horizontal coordinate system (like PCS_WGS84_UTM_zone_15N) and a vertical coordinate system (like 5701 - ODN height). An example is  [http://spatialreference.org/ref/epsg/7405/html EPSG:7405] - OSGB36 / British National Grid + ODN. There is no way to represent this in a GeoTIFF tag and [http://itshumour.blogspot.com/2011/08/funny-statuses-quotes-for-facebook.html funny facebook statuses].
     42* The EPSG and OGC models include an EPSG code for a composite coordinate system. The composite coordinate system is a collection of a horizontal coordinate system (like PCS_WGS84_UTM_zone_15N) and a vertical coordinate system (like 5701 - ODN height). An example is  [http://spatialreference.org/ref/epsg/7405/html EPSG:7405] - OSGB36 / British National Grid + ODN. There is no way to represent this in a GeoTIFF tag.
    4343
    4444== Ellipsoidal Heights ==
     
    4646One way of describing elevations is relative to an ellipsoid rather than to a more specialized vertical datum.  The 1.0 GeoTIFF specification ( [http://www.remotesensing.org/geotiff/spec/geotiff6.html#6.3.4.1 section 6.3.4.1]) listed ellipsoidal VertCS values in the range 5000 to 5033; however, those do not appear to have any corresponding definitions in modern EPSG databases.  I am currently taking the position that it those should therefore be disregarded.
    4747
    48 Instead I propose that we just treat ellipsoidal heights by not specifying any VerticalCSTypeGeoKey code and letting the ellipsoid be determined from the ProjectedCSTypeGeoKey, !GeographicTypeGeoKey or !GeogEllipsoidGeoKey.   Thus a GeoTIFF defined as follows would be assumed to have ellevations in meters relative to the WGS84 ellipsoid [http://www.thefunnyquotessayings.com/random-funny-sayings-and-phrases/ funny sayings and phrases].
     48Instead I propose that we just treat ellipsoidal heights by not specifying any VerticalCSTypeGeoKey code and letting the ellipsoid be determined from the ProjectedCSTypeGeoKey, !GeographicTypeGeoKey or !GeogEllipsoidGeoKey. Thus a GeoTIFF defined as follows would be assumed to have ellevations in meters relative to the WGS84 ellipsoid.
    4949
    5050{{{
     
    6262 * [http://trac.liblas.org/wiki/VerticalCS liblas preliminary Vertical CS proposal]
    6363 * [http://trac.osgeo.org/proj/wiki/VerticalDatums PROJ.4 Vertical Datum Info]
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