Changes between Version 2 and Version 3 of TOWGS84GeoKey

Timestamp:

03/09/11 18:06:24 (14 years ago)

Author:

warmerdam

Comment:

add some notes from Christian.

TOWGS84GeoKey

@@ -23 +23 @@
   In particular, if the DATUM does contain a TOWGS84 clause, and the parameter values are zero, then the receiving application can assume that the writing application believed that the datum is approximately equal to WGS84.
 
+== Parameter Definition ==
+
+{{{
+GeogTOWGS84GeoKey
+
+KeyID = 2062
+Type = 3/7 * DOUBLE
+Values = dX, dY, dZ, Rx, Ry, Rz, dS
+}}}
+
+This key allows the specification of a position vector 7 parameter transformation (as defined by EPSG:9606) between the coordinate
+reference system of the file and the WGS84 system. dX, dY and dZ define the translation vector and are given in meters. Rx, Ry and Rz define the rotation in seconds of an arc. dS is the scale correction expressed in parts per million.
+
+Note that there exists another 7 parameter transformation (the coordinate frame rotation, EPSG:9607) which differs from the method used
+here only in the signs of the rotation parameters Rx, Ry, Rz.
+
+Also the more simple 3 parameter transformation (geocentric translation, EPSG:9603) can be expressed with this geokey by simply setting Rx, Ry, Rz and dS to zero. 
+
 == GeoTIFF Implementation ==