One area the original specification left undefined (perhaps deliberately to reflect handling within EPSG) was how transformation between datums should be accomplished. For the most part this is currently accomplished by applications corresponding GCS/Datum codes with the corresponding EPSG definitions and then selecting among the EPSG provided transformations between datums. However, in the area of projected coordinate systems GeoTIFF took the positions that users could either use an existing EPSG PCS/GCS code or define details of the coordinate system themselves in the GeoTIFF file. This ability is not available for datums.
As one step towards improved self-defining capability in GeoTIFF that captures much existing industry practice it has been suggested a TOWGS84GeoKey be added essentially corresponding to the OGC WKT TOWGS84 keyword. A proposal in this regard is written up at TOWGS84GeoKey and is in use in at least GDAL based applications: http://trac.osgeo.org/geotiff/wiki/VerticalCS
cmheazel
commented
3 years ago
One area the original specification left undefined (perhaps deliberately to reflect handling within EPSG) was how transformation between datums should be accomplished. For the most part this is currently accomplished by applications corresponding GCS/Datum codes with the corresponding EPSG definitions and then selecting among the EPSG provided transformations between datums. However, in the area of projected coordinate systems GeoTIFF took the positions that users could either use an existing EPSG PCS/GCS code or define details of the coordinate system themselves in the GeoTIFF file. This ability is not available for datums.
As one step towards improved self-defining capability in GeoTIFF that captures much existing industry practice it has been suggested a TOWGS84GeoKey be added essentially corresponding to the OGC WKT TOWGS84 keyword. A proposal in this regard is written up at TOWGS84GeoKey and is in use in at least GDAL based applications: http://trac.osgeo.org/geotiff/wiki/VerticalCS