[raster] Add the possibility to aggregate values when rescaling with ST_Rescale()

[pracine]

It would be nice to be able to compute aggregate values when rescaling a raster like this:

​http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z00000034000000.htm

So in addition to the standard resampling algorythms (NearestNeighbor, Bilinear, Cubic, CubicSpline and Lanczos) we could use "sum", "count", "mean", "max", "min", "median".

The count would count the number of pixel with value (ignoring nodata values).

Event if this operation is VERY similar to rescale it could be named ST_Aggregate instead. It would accept a size (in pixel) for the aggregate pixel area and an aggregate type (sum", "count", "mean", "max", "min", "median").

If the resample code base (based on GDAL) could be reuse or if a totally new function has to be written is to be determined.

[dustymugs]

I don't think this will be possible using the established ST_Resample. Using ST_Aggregate is a better solution.

[robe]

Milestone renamed