I am just wondering what the exact function of skewX and skewY in raster constructors is. According to the documentation linked:
ST_MakeEmptyRaster — Returns an empty raster (having no bands) of given dimensions (width & height), upperleft X and Y, pixel size and rotation (scalex, scaley, skewx & skewy) and reference system (srid).
It seems that altogether
(scalex, scaley, skewx & skewy) defines
rotation. But obviously, scalex and scaley also defines the scale operation. This makes me wonder what exactly do these four parameters define.
Is the defined function/transformation equivalent to an affine transformation?
If it's just rotation and scaling, wouldn't it be more efficient to use scalex, scaley and the angle of rotation, e.g. theta?