[gdal-dev] The GeoTransform Array

[Even Rouault]

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

>
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