[Qgis-user] 'gdawarp' causing shift and other questions

[Even Rouault]

Selon Etienne Tourigny <etourigny.dev at gmail.com>:

> 1) Probably a datum issue, as shapefiles do not include datum shift
> information. You could work this around by making a new shape file
> with the same datum as the gtiff file.
>
> What are the datums of your gtiff and shape files?  Please post the
> contents of the .prj file.

It might be the same as http://trac.osgeo.org/gdal/ticket/3947

>
> Etienne
>
> On Mon, Jan 30, 2012 at 9:39 AM, Tilottama Ghosh <waggymaggy at gmail.com>
> wrote:
> > Hi,
> >
> > I have a huge tiff image (covering an entire country) with 3399 columns and
> > 3747 rows, so a total of 12,736,053 cells. The cell size is 1000m or 1km. I
> > need to extract the data per km2. Of course, I didn't think it was smart to
> > work with such a huge dataset in one go. So, I followd these steps in
> > Quantum gis -
> >
> > 1. I used the gdalwarp -crop_to_cutline in the command line to carve out a
> > portion of the raster image based on the shapefile  of a state of the
> entire
> > country. The problem is that although the gdalwarp command worked it is
> > clearly causing a shift (of about 500m) during this step.
> >
> > 2. Then, I used the gdal2xyz tool from the command line to create the csv
> > file corresponding to the 'cut out' raster image or only the raster image
> of
> > the state.
> >
> > 3. Then I used the 'Create a Layer from a Delimited Text file' plugin in
> > qgis to get the centroid shapefile.
> >
> > My problems are-
> >
> > 1. The shift in the image caused by the gdalward tool. Does anyone know how
> > to work around that, so that no shift is caused?
> >
> > 2. The image is in 32 bit floating point and so does not show the attribute
> > table. Even after getting the csv file I am unable to link the created csv
> > file with the raster image, and thus cannot understand which pixel
> > corresponds to which value in the csv file.
> >
> > Can anyone suggest any better way of doing this?
> >
> > Thanks very much for your help.
> >
> > Best Regards,
> >
> > Tilo
> >
> >
> > --
> >
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