[Qgis-developer] Problem with GRASS Region Extent and Region Cellsize on Processing

[Pedro Venâncio]

Hi,

I've been doing some tests on Processing and found something strange with
the GRASS tools, using GRASS Region Extent and Region Cellsize options.

These options work well when doing an operation that aligns the result to a
raster with a smaller extent. Please see this screencast:

https://dl.dropboxusercontent.com/u/5772257/qgis/Processing_grass_region.ogv

The result is perfectly aligned with the base raster.

However, doing the reverse, i.e., performing an operation on a raster,
aligning it to a raster with a greater extent, and a lower resolution, the
resolution fits well, but the pixels are not aligned. It seems that has an
offset exactly the equivalent of half the pixel size. In fact, the
resulting raster gets a greater extent than the reference, by the
equivalent of half the pixel size. Take a look here:

https://dl.dropboxusercontent.com/u/5772257/qgis/processing_grass_region_desviation_half_pixel.avi

I've tested and this happens both on Linux and Windows.

Could this be a bug? In which tool?

Thanks!

Best regards,
Pedro
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