Guillaume Sueur wrote:
Having just realised that gdal doesn't use proj EPSG file for
reprojection (see my previous post on "Unsupported SRS but available in
epsg file"), I have a few questions to clarify the reprojection
processes both in gdal and mapserver :
- where do the gdal gcs/pcs definitions come from ? Is it a separate
repository or proj source files ?
Guillaume,
Yes, the gdal/data/{pcs,gcs}.csv files.
- Doesn't ogr2ogr use proj definition files at all ?
There are special circumstances when the proj.4 epsg init file is
consulted (if no definition is found in the pcs/gcs csv files).
But normally ogr2ogr does not use the proj.4 init files at all.
> Does this mean that
an ogr2ogr reprojected file can be different than a mapserver
reprojection result if proj/epsg definition and gdal pcs defs are
slightly different ?
Yes, this is possible, particularly if someone has hand modified
one or the other.
- If I say "GDAL/OGR uses its own definition files to retrieve proj4
definitions and lets proj4 engine do the reprojection job", am I true ?
Yes.
The last point of note is that the PROJ.4 epsg init file is periodically
generated from the GDAL pcs/gcs.csv files and so they do normally
match quite exactly.
Best regards,
--
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I set the clouds in motion - turn up | Frank Warmerdam, warmer...@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent
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