Mike Jarvis

Rebase this to main and direct PR to main.

If you only have 13 stars, then order 3 polynomial interpolation is going to be very poorly constrained. That has 10 free parameters for each pixel in the PixelGrid. There's...

http://rmjarvis.github.io/Piff/_build/html/index.html

I have no idea what you are doing wrong to get that error message. It's not something that should happen if you are using the PixelGrid model as you mentioned...

I'd guess something to do with the col/row x,y or u,v stuff. I always find that confusing. Have you checked if actually round objects come out measured as round when...

Another thought -- if it's just a bug in the wcs handling, it should be insensitive to the size of the galaxy. Could check with hlr=3 instead of 0.5. If...

Sounds like the first unit test to write is that Gaussian fit and moments give consistent answers when the wcs is sheared.

I was summoned. But I'm not sure, do you need me to look at this?

Except the schema you linked to defines `position_angle` as "Position angle (arctan(E2/E1)), for galaxy, lensed", which is not the same as the traditional astronomy definition of [position angle](https://en.wikipedia.org/wiki/Position_angle). So this...

My point was just that I don't know if the `pos_angle` that is being applied here is the same one we have in imsim. If it is the same PA,...