id	summary	reporter	owner	description	type	status	priority	milestone	component	version	severity	resolution	keywords	cc
986	postage stamp coordinates are off for megacam spliced images	bills	bills	"The command

ppstamp out -file 870505p.fits -skycenter 1:16:32.948 8:23:25.65 -pixrange 200 200

should generate a postage stamp with an object that looks like a galaxy
at the center.

Instead the object is 32 pixels left of center.

The image is extracted from a mosaic image created with pmChipMosaic

       // readout is from the mosaic
        psImage *subsetImage = psImageSubset(readout->image, options->roi);
        
        // make a copy since we're going to change the image's internals
        outReadout->image =psImageCopy(NULL, subsetImage, subsetImage->type.type);
        P_PSIMAGE_SET_COL0(outReadout->image, 0);
        P_PSIMAGE_SET_ROW0(outReadout->image, 0);

where options->roi is a region centered on the chip coordinates for the object.
Pixel (1943, 3251)

The problem is that the coordinate system changes in the process of mosaicking
the chip.

If the image is extracted using the readout for the original input image
instead of the mosaic, the correct pixels are extracted.

Looking at the mosaic image we find that it is has col0=row0=0 and
so is effectively shifted to the left as well. 

32 pixels is size of the overscan region."	defect	assigned	lowest		ppstamp	unspecified	normal		IPP