[Gdal-dev] Re: [GRASSLIST:6160] Re: r.proj and gdawarp give differernt results

[Maciek Sieczka]

Frank

I would be happy to assist you in sorting things out but but based on your
latest reply I don't understand what you want me to do. Please clear it out
to me.

Cheers
Maciek

P.S.
Not being online I usually answer with quite a delay.


From: "Frank Warmerdam" <fwarmerdam at gmail.com>
> On Mon, 14 Mar 2005 13:39:54 +0100, Maciek Sieczka <werchowyna at epf.pl>
> wrote:
>>     6. both gdalwarp and r.proj product have the *same* number of
>> columns,
>>     rows and res but the extent and apperance are still somewhat
>> different:
>
> Maciek,
>
> I think this is a very significant issue.  The difference in
> georeferencing seems
> to be only a small portion of a pixel, but this can frequently be
> significant.
>
> To test I tried tracking back one pixel that was different in the two
> warpers.  I
> tracked back the center of a pixel from the GDAL warp output:
>
> Output Location
> ---------------
>
> Value: 82
> Pixel/Line = 39.5, 138.5
> Georef     = 337548.161466, 277562.731833
>
>
>
> Input Location
> --------------
>
> cs2cs -f '%.6f' +init=epsg:2180 +to +init=epsg:32633
>
> Georef: 622113.023072   5578151.357107
>
> Pixel/Line: 36.054, 136.782
>
> Value: 82
>
> So, in this case the GDAL result seems to be proper, but the
> difference in georeferencing between the r.proj and gdalwarp
> output images is approximately 1.28 meters or approximately
> 0.08882 pixels which would account for the sampling coming
> from the neighbouring pixel (which we see in the r.proj result).
>
> I have not traced any other pixels.  My suggestion is that you
> do what you need to do to get exactly the same georeferencing
> in both output products and then compare the results.  If there is
> still a difference then try tracking back some pixels to see why
> they differ (well - at least which is correct).
>
> Best regards,
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows | http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Programmer for Rent
>
>