Changes between Version 2 and Version 3 of VerticalCS

Timestamp:

02/07/11 10:56:54 (14 years ago)

Author:

warmerdam

Comment:

--

VerticalCS

@@ -42 +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.
 
+== Ellipsoidal Heights ==
+
+One 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.
+
+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. 
+
+{{{
+   Keyed_Information:
+      GTModelTypeGeoKey (Short,1): ModelTypeGeographic
+      GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
+      GeographicTypeGeoKey (Short,1): GCS_WGS_84
+      GeogCitationGeoKey (Ascii,7): "WGS 84"
+      End_Of_Keys.
+}}}
+
+
 == Related Resources ==