Unable to solve small fields

[Samuel Grund]

Hi all,

I have a few things I've been working on improving or fixing for a while, so here it goes:

The largest field size of my images are around 6x6 arcminutes and I can solve these in around 4-5 seconds (on a relatively beefy machine). To do this I downsample my images and provide a ra and dec and a radius of 0.2 degrees (which is actually quite big considering the field size, but lower than that and it sometimes fails). Here are the CLI parameters I use:

                '--extension', '1',
                '--no-plots',
                '--overwrite',
                '--dir', '/tmp/',
                '--downsample', str(int(4/frame.binning[0])), # This is just to ensure that the product pixel size will be the same even for differently binned images
                '--fits-image',
                '--ra', str(frame.target_ra_deg),
                '--dec', str(frame.target_dec_deg),
                '--radius', '0.2',  # degrees

I have also been trying to solve some .fits files with field sizes of around 2.85 x 2.85 arcmin on my local astrometry installation. They already contain a WCS accurate to a few arcseconds (which is not sufficient in my case), but for some reason I am unable to solve these images. I believe I have sufficient index files (please see below), and the nova.astrometry.net solver is able to do it in only around a second. What gives?

So here are my questions

- How can I successfully solve the smaller frames?

- Can I somehow optimize the solver parameters to speed up my system in general?

I have attached two images that are representative of my data.

ALIa310083 is the larger 6x6 arcmin image while ALIa310084 is the smaller of the two.

In my astrometry config I have the following flags set:

- inparallel

- autoindex

and I have the following index files:

- 5201-00 -> 5201-47

- 5202-00 -> 5202-47

Any help is much appreciated.

Best wishes,

Sam

[Samuel Grund]

[Samuel Grund]

[Dustin Lang]

Hi,

2.85 arcmin is pretty small - the 5201 index files (scale 01) contain quadrangles of stars with diameters from 2.8 to 4.0 arcmin, so you would be very unlikely to find one fully container in your image.  You'll need at least the "00" index files, and you might even want the "m1" ("minus one") scale; https://portal.nersc.gov/project/cosmo/temp/dstn/index-5200/LITE/

The nova.astrometry.net solver has the 00 scale, so that's probably why it can solve them.

As for speeding things up: by far the best thing you can do is give it an estimate of the pixel scale or image size via the "--scale-low", "--scale-high", "--scale-units" args.

cheers,

dustin

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