[Proj] using an NTv2 grid to apply a slight shift to coordinates in a metric CS
andre+joost at nurfuerspam.de
Thu Jan 3 11:25:23 EST 2013
the nadgrid shift is usually done with lat/lon coordinates. You
transform your cartesian coordiantes to lat/lon, apply the shift, and
transform into another grid.
The syntax of the proj string is:
+proj=tmerc +lat_0=0 +lon_0=9 +x_0=3500000 +y_0=0 +k=1.000000
+ellps=bessel +units=m +nadgrids=path/to/BETA2007.gsb +wktext
The grid file has to be in binary format, which can be transformed from
an ASCII file.
For the German grid, information can be found here:
Most other users of NTv2 should have published similar documentation.
Am 03.01.2013 15:03, schrieb Maciej Sieczka:
> I have a script which takes an x,y pair of metric coordinates in
> EPSG:2174 (http://www.spatialreference.org/ref/epsg/2174/proj4) and
> returns them slightly shifted, in the same coordinate system.
> The difference between the input and output coordinates varies from 0
> to about 60 cm, non-systematicaly.
> I would like to be able to "reproject" my GIS data from EPSG:2174 to
> EPSG:2714 + the shift described above, and the other way round; using
> GDAL/OGR, GRASS, QGIS reprojection tools.
> Can anyone tell me if using a shift grid for that would make sense? I
> have a general idea how to create one from my scripts output, but there
> is something missing in my thinking. Let me put it this way - should my
> grid provide shifts between:
> a) the original EPSG:2174 and the EPSG:2174+shift
> or rather
> b) between WGS84 and the EPSG:2174+shift?
> And what would be the proj4 string for the new system in either case?
> Another thing is if it would be possible to utilise a similar grid to
> reproject between EPSG:2714+shift and other coordinate systems covering
> the same territory (e.g. EPSG:2180), again using GDAL etc. tools.
> Ideally, I would like to achieve both goals with just single shift
> I'm afraid I might be asking my questions wrong way, but hopefully you
> get what I'm aiming at. I'd be grateful if you can correct my errors and
> give me some guidance here.
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