Opened 15 years ago
Closed 14 years ago
#2639 closed defect (fixed)
Proj policy since 4.6.0 to require datum shift into explicitly causes problems in transformations
Reported by: | Ari Jolma | Owned by: | warmerdam |
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Priority: | normal | Milestone: | |
Component: | OGR_SRS | Version: | unspecified |
Severity: | normal | Keywords: | datumshifts |
Cc: |
Description
GDAL uses Proj for coordinate transformations. Transformations are based on presenting spatial reference systems as proj strings to proj. Proj strings are made from pcs.csv etc files. Since 4.6.0 Proj requires explicit datum shift info, i.e., +towgs84 parameter. This is not created for some projections due to how coordinate systems are represented in gcs.csv.
See also Proj ticket 15 http://trac.osgeo.org/proj/ticket/15
Change History (5)
comment:1 by , 15 years ago
Component: | default → OGR_SRS |
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comment:2 by , 15 years ago
Keywords: | datumshifts added |
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comment:3 by , 15 years ago
NIMA TR8530.2 (http://earth-info.nga.mil/GandG/publications/tr8350.2/tr8350_2.html) says (according to an official finnish document JHS 153) that ETRS89, which is based on ITRS, can be considered identical to WGS84.
comment:4 by , 14 years ago
The "big libgeotiff datum update" sets the ETRS89 datum shift to 0,0,0. I will leave this ticket open pending this update going into GDAL.
comment:5 by , 14 years ago
Resolution: | → fixed |
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Status: | new → closed |
csv init files updated in trunk (r18978).
Ari,
Is ETRS89 explicitly equivelent to WGS84? Can you provide references?
Our normal practice is to include "shift to wgs84" info for datums if there is one and only one shift offered in the EPSG database. If there are more than one or none we don't do anything with the exception of a few reasonably carefully considered overrides which go into gcs.override.csv in libgeotiff.
I'd appreciate it if you could back out r15649 in GDAL. Updates for GCS overrides need to be addressed at the libgeotiff level of the processing chain, and I think merit discussion before application.
The EPSG initialization file explicitly does not have towgs84 parameters for many datum because we don't know the shifts that are appropriate. Providing +towgs84=0,0,0 just fools people into thinking we know what to do when we don't. The current approach is predicated on the principle of doing nothing (datum shift wise) unless we actually know what to do with some authority.