Opened 14 years ago

Closed 12 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
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 warmerdam, 14 years ago

Component: defaultOGR_SRS

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.

comment:2 by warmerdam, 14 years ago

Keywords: datumshifts added

comment:3 by Ari Jolma, 14 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 warmerdam, 12 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 warmerdam, 12 years ago

Resolution: fixed
Status: newclosed

csv init files updated in trunk (r18978).

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