[gdal-dev] Geotransform - rotation and translation

[Jan Hartmann]

The only way would be then to concatenate the transformations: first 
rotate and then translate half a pixel width. The computation can be 
simplified by matrix multiplication:

http://www.mathplanet.com/education/geometry/transformations/transformation-using-matrices

Jan
> That won't work, since it will move the corner point half a cell, and 
> then rotate around the new corner.
>
> - Øyvind
>
>
> On Mon, Aug 26, 2013 at 7:02 PM, Norman Vine <nhv at cape.com 
> <mailto:nhv at cape.com>> wrote:
>
>
>     On Aug 26, 2013, at 12:50 PM, Oyvind Idland
>     <oyvind.idland at gmail.com <mailto:oyvind.idland at gmail.com>> wrote:
>
>>     I am currently working on a driver for a proprietary format,
>>     which is being consumed by ArcGis via GDAL.
>>
>>     These grids sometimes has a rotation with a specified pivot
>>     point. I managed to get ArcGis to display the rotated grid by
>>     doing the following:
>>
>>     poDS->dGeoTransform[0] = originX;
>>     poDS->dGeoTransform[1] = cos(rotation) * cellSizeX;
>>     poDS->dGeoTransform[2] = -sin(rotation) * cellSizeX;
>>     poDS->dGeoTransform[3] = originY;
>>     poDS->dGeoTransform[4] = sin(rotation) * cellSizeY;
>>     poDS->dGeoTransform[5] = cos(rotation) * cellSizeY;
>>
>>     Rotation is in radians. It works, but there is one problem: I
>>     need to rotate the grid around the center of the corner cell
>>     (originX, originY), but ends up getting rotation around the
>>     corner of the cell/raster instead.
>>
>>     There is a screenshot here, showing only the corner pixel. The
>>     topmost grid/pixel was translated using custom geotransform in
>>     ArcGis, the bottom one is the result of my GDAL rotation:
>>     The cyan dot shows the pivot point:
>>
>>     http://i.stack.imgur.com/7HEvc.png
>>
>>
>>     Is there any way to express this translation using the
>>     geotransform matrix ?
>
>     I think this should work
>
>     poDS->dGeoTransform[0] = originX + cellSizeX/2.0;
>     poDS->dGeoTransform[1] = cos(rotation) * cellSizeX;
>     poDS->dGeoTransform[2] = -sin(rotation) * cellSizeX;
>     poDS->dGeoTransform[3] = originY - cellSizeY/2.0;
>     poDS->dGeoTransform[4] = sin(rotation) * cellSizeY;
>     poDS->dGeoTransform[5] = cos(rotation) * cellSizeY;
>
>
>
>     _______________________________________________
>     gdal-dev mailing list
>     gdal-dev at lists.osgeo.org <mailto:gdal-dev at lists.osgeo.org>
>     http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
>
>
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20130827/4ad8f3e1/attachment-0001.html>