Drawing an image of PSF with custom radial profile in GalSim

Question

I have a radial profile of a point spread function (PSF) that I want to draw in GalSim, so that I can call FindAdaptiveMom on the resulting image. The profile is in units of normalized intensity vs. angular position in arcseconds. I have looked at the instructions for building a custom object, but am wondering if it's possible to render a GalSim Image without building an object? If not, would it be possible to build an object simply by reading in the profile?

Answer 1

Unfortunately, it's not currently very easy to roll your own custom profile in GalSim. The instructions you pointed to would require the output to still be generated in terms of existing galsim types, so not really what you're looking for.

I think you have two options:

1. If all you care about is the FindAdaptiveMom bit and you don't want to do anything complicated with the rendering, you can lay down the radial profile yourself. An image is mostly just a wrapper around a numpy array and a bounds (defining what coordinate the origin of the array is). So you could write that array yourself and then make an image from that with im = galsim.Image(array) and call FindAdaptiveMom on that.

2. If you want your radial profile to be the true surface brightness profile on the sky (rather than as seen on an image) and then properly render it including integration over the pixels, then that's a little trickier. You can coerce GalSim into doing that by doing the above rendering first, and then make a galsim.InterpolatedImage object out of that, which will treat the drawn image as a surface brightness profile, which can then be drawn in the usual way (drawImage).