[gdal-dev] GeomTransform in VRT-file

[Jan Hartmann]

Reading the documentation always helps. The GeomTransform takes the 
upper left corner as the origin, not the lower left, as in my math 
handbook. And the order of the coefficients is  <c b a f e d> With some 
twiddling of angles and signs I now can compute the affine 
transformation of a scan based on two control points. That means that 
with the vrt-file and its geomtransform it is possible to georeference a 
scan in real time without warping, at least for a first order 
polynomial. Marvelous!

Thanks for your help.

Jan

On 07/04/2013 09:58 PM, Dmitriy Baryshnikov wrote:
> Hi Jan,
>
> Do you mean this : http://www.gdal.org/gdal_datamodel.html (Affine 
> GeoTransform srection) or this http://www.gdal.org/gdal_tutorial.html 
> (Getting Dataset Information section)?
> Also, see this: 
> http://www.gdal.org/classVRTDataset.html#a1531325b71e290b90c8d9cc88bce6c2b
>
> Best regards,
>     Dmitriy
>
> 04.07.2013 20:12, Jan Hartmann пишет:
>> I'm struggling with the order of the Geotransform section in a vrt 
>> file. I would like to rotate an image, and computed the six 
>> parameters for the affine transformation. I can transform points 
>> exactly, using the following formula:
>>
>> x2 = a.x1 + b.y1 + c
>> y2 = d.x1 + e.y1 + f
>>
>> Can anyone tell me what the order is in the GeoTransform section of 
>> the VRT-file?
>>
>> <GeoTransform> c a b f d e </GeoTransform>
>>
>> results in an image somewhere in the neighbourhood, but mirrored and 
>> translated. What is the order of the parameters a-f?
>>
>> Jan
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>>
>
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