Allow the fitting region to be circular in PSF Photometry

[mirca]

Currently the fitting region is defined by the fitshape parameter which defines a rectangular region around the (initial guess) center of the source.

It would be great to be able to perform the fit in a circular region.

I see this being implemented by allowing fitshape to be an CirclePixelRegion (from regions) object which defines the fitting region.

[larrybradley]

Yes, that would be nice.

It may be better (more general) to allow fitshape to be a "footprint" array (essentially an array of ones and zeros like a mask). Such an array can be generated from apertures or regions using the to_mask() method.

Here's an example of a footprint: http://photutils.readthedocs.io/en/latest/api/photutils.detection.find_peaks.html?highlight=footprint