Healpix aliasing warning

[nicholebarry]

I vaguely remember there being some sort of aliasing issue regarding changing the gridding size going into Healpix. I recently ran into that again.

Bryna, can you remind me what the issue is...and would it be possible to add a warning message in FHD?

Example: Gridding going into Healpix was set at 2 wavelengths per pixel (as apposed to 1/2 wavelengths per pixel). Result: Weird folding happens in the image

[bhazelton]

The standard Healpix pixels that we have FHD grid to are picked based on the uv pixel size and the desired image extent. But you should never have a larger extent than can be generated by the uv pixel size you're working with. Larger pixel sizes result in smaller image extents that won't be aliased. We could maybe check that the image extent isn't too big for the uv pixel size and issue a warning. But Healpix image extents are a little challenging to figure out because of the non-regular gridding...

[nicholebarry]

What if we save the uv pixel size used to help generate the Healpix index files in the Healpix index file itself (and then check against that)? Would that be more or less complicated?

[bhazelton]

We might already have it if its in the obs structure...