[Proj] Misplaced SHP obtained with PROJ 4.8.0 called from gvSIG CE
peifer at gmx.eu
Mon Aug 26 11:17:12 EST 2013
On 2013-08-26 16:33, Andre Joost wrote:
> Am 26.08.2013 14:54, schrieb Jorge Arevalo:
>> Actually, my SRSs are:
>> source SRS: +proj=tmerc +lat_0=0.0 +lon_0=-3.0 +k=0.9996 +x_0=500000.0
>> +y_0=0.0 +ellps=intl +units=m +nadgrids=sped2et.gsb
>> target SRS: +proj=tmerc +lat_0=0.0 +lon_0=-3.0 +k=0.9996 +x_0=500000.0
>> +y_0=0.0 +ellps=GRS80 +units=m
> The second one is missing +nadgrids or +towgs84. Without it, proj does
> not make a datum shift, but assumes both CRS to have the same datum.
As André wrote: PROJ.4 version >= 4.6.0 needs a datum specification for
*both* source SRS and target SRS in order to "make the datum shift".
For PROJ.4, a datum is the definition of an ellipsoid (via +ellps, +a,
+rf, etc.) in combination with either the +towgs84 or the +nadgrids
parameter. This could mean in your case: +towgs84=0,0,0 or +nadgrids=@null
+nadgrids=@null is more appropriate as your grid shift file has ETRS89
offsets (rather than WGS84 offsets, as assumed by PROJ). Practically,
the difference between both options is in the sub-millimeter range,
hence irrelevant in most cases.
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