[Gdal-dev] GeoTiff pixel resolution interpretation with gdalinfo

[mattia]

Yes, what I need is to "resize" the pixel. Being the image taken from the
satellite, it skews the far away pixels, mainly ones towards the edges of
the bounding box. I need to execute a bow-tie correction, then somehow
"compress" the pixels to a square resolution. Does that sound feasable? I
will try the command.

Cheers

Mattia

On 5/3/07, Frank Warmerdam <warmerdam at pobox.com> wrote:
>
> mattia wrote:
> > Coordinate System is:
> > PROJCS["HDFLook: LINEAR",
> >     GEOGCS["unnamed",
> >         DATUM["unknown",
> >             SPHEROID["unnamed",6370997,0]],
> >         PRIMEM["Greenwich",0],
> >         UNIT["degree",0.0174532925199433]],
> >     PROJECTION["Equirectangular"],
> >     PARAMETER["latitude_of_origin",0],
> >     PARAMETER["central_meridian",0],
> >     PARAMETER["false_easting",0],
> >     PARAMETER["false_northing",0],
> >     UNIT["metre",1,
> >         AUTHORITY["EPSG","9001"]]]
> > Origin = (8912408.472916,7090227.412053 )
> > Pixel Size = (694.49452741,-1000.15538912)
> ...
> > Is my interpretation correct? The pixel resolution as indicated is in
> > meters... Accordingly 694 meters horizontally (X res) , 1000 meters
> > vertically (Y res)?!?!
>
> Mattia,
>
> That is correct.
>
> > What is the minus sign i front of the Y res for???
>
> It means that as you step "down" the image from the top left corner you
> subtract 1000m per pixel step from the y coordinate.  This is normal.
>
> > What is the UNIT["degree",0.0174532925199433]], factor in this output??
> > can I use it to define the resolution?? Or what is it needed for??
>
> This indicates that one degree on the underlying geographic
> coordinate system is 0.017... radians.  It is standard and does
> not help you for what you want to do.
>
> > Final question,
> >
> > Is there a stright forward way of changing the image's resolution so as
> > to have a quadratic one whereby resX=resY ????
>
> I didn't follow that I'm afraid.  Are you just wanting to resample
> your image to have square pixels?  You could do something like:
>
> gdalwarp -rb -ps 694 694 Area1.tif Area1SquarePixels.tif
>
> This would use a bilinear resampling kernel to convert your
> image from 694x1000 meter pixels to 694x694 meter pixels.
>
> 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    | President OSGeo, http://osgeo.org
>
>


-- 
Mattia
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