WMS layer produces incorrect worldfile cell size distorting cascaded layers

[warmerdam]

The following logic in mapwmslayer.c produces the wrong cell size:

            double dfCellSizeX = MS_CELLSIZE(pasReqInfo[iReq].bbox.minx,
                                             pasReqInfo[iReq].bbox.maxx, 
                                             pasReqInfo[iReq].width+1);	
            double dfCellSizeY = MS_CELLSIZE(pasReqInfo[iReq].bbox.maxy,
                                             pasReqInfo[iReq].bbox.miny, 
                                             pasReqInfo[iReq].height+1);

The problem is that MS_CELLSIZE() is designed for MapServer "center of pixel" extents but WMS bounding boxes are outer edge of pixels. The fix is to use width+1 and height+1.

I have a test case to demonstrate this but the data is potentially not redistributable. I can, if necessary, produce a redistributable demonstration.

[warmerdam]

Proposed Fix.