[postgis-devel] [wktraster] Regular blocking and rotation

[Frank Warmerdam]

Mateusz Loskot wrote:
> Hi,
> 
> I think rotation property of regular blocking needs to be
> specified explicitly and clearly in the WKT Raster specification.
> 
> Current document [1] makes explicit use of word "rotation" only once:
> 
> "
> 5. The extent field must be a simple rectangle (non-rotated).
> "
> 
> Next, there is no rotation included in the schema of RASTER_COLUMNS table.
> 
> It seems to be enough to conclude that regular blocking coverage
> is never rotated. But, is this conclusion correct?
> I've scanned through all archived WKT Raster discussions 
> and I couldn't find any confirmation.
> 
> [1] http://trac.osgeo.org/postgis/wiki/WKTRaster/SpecificationWorking01

Mateusz,

This document includes methods like ST_SkewX and ST_SkewY, and the
ST_GeoReference() appears to return a full affine geotransform for
a tile, so I conclude that tiles can be rotated.

However, the RASTER_COLUMNS table does not include any mechanism to
return the full 6 parameter affine transformation for a rotated/skewed
image.   I conclude that regular blocked images cannot currently be
rotated otherwise it would be impossible to determine the georeferencing
from the RASTER_COLUMNS table.

I would suggest we add skew_x, and skew_y columns in RASTER_COLUMNS so
that rotated and skewed regulary blocked images are supported.

Best regards,
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