Changes between Version 2 and Version 3 of TOWGS84GeoKey


Ignore:
Timestamp:
Mar 9, 2011 6:06:24 PM (9 years ago)
Author:
warmerdam
Comment:

add some notes from Christian.

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  • TOWGS84GeoKey

    v2 v3  
    2323  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.
    2424
     25== Parameter Definition ==
     26
     27{{{
     28GeogTOWGS84GeoKey
     29
     30KeyID = 2062
     31Type = 3/7 * DOUBLE
     32Values = dX, dY, dZ, Rx, Ry, Rz, dS
     33}}}
     34
     35This key allows the specification of a position vector 7 parameter transformation (as defined by EPSG:9606) between the coordinate
     36reference 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.
     37
     38Note that there exists another 7 parameter transformation (the coordinate frame rotation, EPSG:9607) which differs from the method used
     39here only in the signs of the rotation parameters Rx, Ry, Rz.
     40
     41Also 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.
     42
    2543== GeoTIFF Implementation ==
    2644