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- Projection string management: GRASS GIS relies on GDAL/PROJ.
- The EPGS DB is transformed into suitable CSV data for GDAL/PROJ
- according to this procedure:
- http://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/README
- The EPSG CSV files are used via GDAL/OGR API from
- gdal-config --datadir
- The datum shift grids are also used from GDAL/PROJ (proj-nad package).
- TODO: It is recommended to rely on PROJ4's proj-nad package. For doing so,
- there would be some changes needed to lib/proj/get_proj.c - the call
- to pj_set_finder() should be removed so that PROJ looks in its default
- locations for the files.
- Function:
- const char* pszDatumshiftfile = CPLFindFile( "gdal", "datum_shift.csv" );
- ##########
- # EPSG code queries:
- # printing all available datum shift codes
- ogrinfo /usr/share/gdal/datum_shift.csv -al
- ogrinfo /usr/share/gdal/gcs.csv -al
- # selective printing
- ogrinfo /usr/share/gdal/datum_shift.csv -al -where "SOURCE_CRS_CODE = '4156'" -al
- ogrinfo /usr/share/gdal/gcs.csv -al -where "COORD_REF_SYS_NAME LIKE '%JT%'"
- # print NAD file info
- gdalinfo /usr/share/proj/hawaii
- # query codes
- gdalsrsinfo EPSG:5514
- # transform between projections
- gdaltransform -s_srs EPSG:4326 -t_srs "+proj=longlat +datum=nad27" --debug on
- ##########
- # Testing: comparing results
- # Testing using GDAL
- PROJ_DEBUG=ON CPL_DEBUG=ON gdaltransform -s_srs EPSG:4326 -t_srs "+proj=longlat +datum=nad27"
- -100 40
- -99.9995941840488 39.9999941029394 0
- # Testing using GRASS GIS
- PROJ_DEBUG=ON CPL_DEBUG=ON m.proj proj_in="+init=epsg:4326" proj_out="+proj=longlat +datum=NAD27" coordinates=-100,40 -d
- -99.99959418|39.99999410|0.00000000
- The resulting values need to be identical (note: m.proj prints with less precision)
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