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TOWGS84GeoKey #6

Open tedhabermann opened 9 years ago

tedhabermann commented 9 years ago

This problem is described by Frank Warmerdam on the Refining GeoTIFF page.

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.

rouault commented 5 years ago

This should become a lesser relevant topic once PROJ and GDAL versions that implement late-binding capabilities are available (resp PROJ 6 and GDAL 2.5), although GeoTIFF files with a TOWGS84GeoKey might still be found.

rouault commented 4 years ago

TOWGS84GeoKey is actually becoming a nuisance in the GDAL ecosystem now we are transitioning to GDAL 3 and PROJ 6/7. See https://github.com/OSGeo/gdal/issues/2312 for an illustration of this. So my suggestion would not to standardize it and let it as a past hack.

rouault commented 3 years ago

We should probably extend Annex E ( http://docs.opengeospatial.org/is/19-008r4/19-008r4.html#_summary_of_geokey_ids_and_names ) to mention that TOWGS84GeoKey=2062 is a reserved geokey, even if not standardizing it. That will avoid any potential later conflict / reuse for other purposes . Should be targetted for 1.2

rouault commented 3 years ago

Pull request to reserve the value: https://github.com/opengeospatial/geotiff/pull/98

desruisseaux commented 1 year ago

Should we close this issue? The key has been declared as reserved by #98 (merged), and it should not be needed by late binding implementations of map projection libraries. This key may still be useful if a GeoTIFF file uses a CRS which is not defined in the EPSG database, but is it a need common enough for addressing this issue?