[gdal-dev] The GeoTransform Array

[Mateusz Loskot]

On 21 November 2012 12:06, Even Rouault <even.rouault at mines-paris.org> wrote:
> Selon David Strip <gdal at stripfamily.net>:
>
>> The GDAL API tutorial describes this array as:
>>
>>      adfGeoTransform[0]/* top left x */
>>      adfGeoTransform[1]/* w-e pixel resolution */
>>      adfGeoTransform[2]/* rotation, 0 if image is "north up" */
>>      adfGeoTransform[3]/* top left y */
>>      adfGeoTransform[4]/* rotation, 0 if image is "north up" */
>>      adfGeoTransform[5]/* n-s pixel resolution */
>>
>> The GDAL Data model page says
>>      Xgeo = GT(0) + Xpixel*GT(1) + Yline*GT(2)
>>      Ygeo = GT(3) + Xpixel*GT(4) + Yline*GT(5)
>> where the GT[i]are the coeffs described above.
>>
>>  From this I conclude that the rotations are not sin/cos of the rotation, but
>> rather the sin/cos times the
>> appropriate pixel size. Is that right, or did I miss something?
>
> Yes, for a pure rotation. If the [1], [2], [4] and [5] have no particular
> relation, the matrix can represent a combination of scaling, rotation and
> shearing. See http://en.wikipedia.org/wiki/Transformation_matrix

Isaac's "Improving the Documentation of Get/SetGeoTransform" post is
worth checking too:

http://lists.osgeo.org/pipermail/gdal-dev/2011-July/029449.html

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net