[gdal-dev] Geotransform - rotation and translation

[Oyvind Idland]

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> wrote:

>
> On Aug 26, 2013, at 12:50 PM, Oyvind Idland <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;
>
>
>
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