[gdal-dev] An issue about using GDALWARP to do theNTv2transformation

[heng.feng]

Hi Uwe,

Thanks for your reply. The l0.tif file does not contain any georeferenced information. However, I have run the GDALINFO command on another raster data file which is in the same map data set provided by the customer and hence is supposed to be georeferenced in the way as the l0.tif file. The command output is sent as attached. As mentioned before, I also did the NTv2 transformation on  this raster data file (Notrufzonen_50m_v11_6_EPOS.tif) with the same GDALWARP command and the same grid shift file. I also got a lot of error messages saying that some coordinates are outside the area of the grid shift file. And with the "+x_0=500000" parameter, the output error messages are much less than the ones with the "+x_0=4500000" parameter.

Thanks for your help again.

BR,
Heng

From: Schmitz, Uwe [via OSGeo.org] [mailto:ml-node+5852724-406096449-308251 at n2.nabble.com]
Sent: 20 December 2010 18:51
To: Heng Feng
Subject: AW: [gdal-dev] An issue about using GDALWARP to do theNTv2transformation

Heng,

>
>
> http://osgeo-org.1803224.n2.nabble.com/file/n5848200/gdalwarp_<http://osgeo-org.1803224.n2.nabble.com/file/n5848200/gdalwarp_?by-user=t>
> problem1.doc
> gdalwarp_problem1.doc
> Hi Uwe,
>
> I have tried your suggestion on the same raster file with a modified
> "+x_0=500000" parameter in the command line (as seen in the
> attached doc). I
> could see the major difference:there is still one error
> message left. When I
> tried on another raster file with the same modified
> parameter, I have got
> much less error messages than before. However, is it still
> possible that my
> raster data are outside the area of the grid shift file? All
> the raster data
> I was trying to transform are GK (DHDN) zone 4, which false
> easting value is
> 4500000. This was why I used "+x_0=4500000" instead of
> "+x_0=500000" in the
> command line. As I am getting to know all these georeference
> settings at the
> moment, can you tell me why you suggested the modified
> parameter and what
> you meant about "raster data lacks the Gauss-Krueger meridian prefix"?
>
that was just a guess, because your coordinates lie far in the
west of DHDN/GK zone 4.
Normally DHDN/GK coordinates are noted as e.g.:
4500000.0 Rechts 5500000.0 Hoch

Omitting the Gauss-Krueger meridian prefix you have:
 500000.0 Rechts 5500000.0 Hoch
(Note: Rechts coordinate has only six digits) an thats
far in the west of the real position. It's very simple and
therefore you may give it a try.

If it's not the case, may be you can post the output of:
gdalinfo l0.tif

That would help to see, if the file is correctly georeferenced.

Regards
Uwe
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