[Proj] Build GDAL with NADSHIFT's

[Roger Bivand]

Even Rouault <even.rouault <at> spatialys.com> writes:

> 
> SriRam,
> 
> I had never saw a .prj with a METADATA node until now. Oh well... It just 
> seems to indicate NAD 83(2011) and the 4 first parameters of METDATA are the 
> bounding box in long/lat of validity for the SRS.
> 
> If you don't need a very accurate reprojection, you could just use -s_srs 
> "+proj=longlat +datum=NAD83" in ogr2ogr.
> 
> If you need very accurate reprojection (let's say error < 1 meter), you could 
> go with the tutorial at https://trac.osgeo.org/proj/wiki/HTDPGrids . But that 
> will be much more involved.


Something like this was seen in August, and rgdal::spTransform now says:


     "Note that WGS84 is both an ellipse and a datum, and that since
     1984 there have been changes in the relative positions of
     continents, leading to a number of modifications. This is
     discussed for example in <URL:
     http://www.uvm.edu/giv/resources/WGS84_NAD83.pdf>; there are then
     multiple transformations between NAD83 and WGS84 depending on the
     WGS84 definition used. One would expect that “+towgs84=” is a
     no-op for WGS84, but this only applies sometimes, and as there are
     now at least 30 years between now and 1984, things have shifted.
     It may be useful to note that “+nadgrids=@null” can help, see
     these threads: <URL:
     https://stat.ethz.ch/pipermail/r-sig-geo/2014-August/021611.html>,
     <URL:
     http://lists.maptools.org/pipermail/proj/2014-August/006894.html>,
     with thanks to Hermann Peifer for assistance."

in its help file. That might suggest dropping the *.prj file and replacing
the input srs definition with +nadgrids=@null as the trick needed. It would
be helpful to know what software generated the *.prj file.

Roger
> 
> Even
> 
> > Hi
> > I have a below .prj file
> > 
> > GEOGCS["GCS_NAD_1983_2011",DATUM["D_NAD_1983_2011",SPHEROID["GRS_1980",6378
> > 137.0,298.257222101]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199
> > 433],METADATA["USA - CONUS and Alaska;
> > PRVI",167.65,14.93,-63.89,74.71,0.0,0.0174532925199433,0.0,1511]]
> > 
> > Can someone guide me how to project a Shape file with the below prj File.
> > Testepsg is giving a failure for the above prj file.
> > 
> > Let me know if anyone has used this earlier... To use the Conus and Alaska
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