[gdal-dev] Guidance sought on using gdal-translate

[Frank Warmerdam]

Christopher Hunt wrote:
> Hi Frank et. al,
> 
> Sorry to be a pest. I've been trying tons of things, trawling tons of 
> search results, and I'm really no better off than I was a few days ago. :-P
> 
> In summary I have an aerial photo image of an airport with three well 
> known points (expressed in lat/longs). I'm wanting the image to be 
> projected using a equidistant cylindrical projection.
> 
> On gdal_translate's gcps, I'm presuming that the origin of the image is 
> assumed to be top-left for the gcp pixel and line values... and that the 
> gcp easting and northing values are expressed in metres?

Chris,

Correct.

> How do I centre a projection? lat_0 and lon_0 values?
> 
> Thanks again for your time - I appreciate that time is precious.

I honestly believe that reprojection is the wrong tool to take a raw
aerial photo and try to turn into an orthophoto.  Normally this process
is address by orthorectification software that takes into account the
geometry of the camera lens, the orientation of the camera when the photo
is taken, and the elevation model of the target region.

If you are going to try and accomplish orthorectification by something as
simple as reprojection then the fit is going to be relatively poor in all
but the most ideal circumstances.

So, sorry to say it, but I'm not going to wrack my brain to try and solve
a problem that I think is likely insolvable.

Best regards,
-- 
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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