Can I specify what catalogue I want used for astrometry.net solution?

[Katie Breeland-Newcomb]

Hello,

I'm working on determining the best practices for digitizing photographic plates and am using astrometry.net to find astrometric solutions. I am currently trying to compare the solutions found when I use different tools to find sources on the plate. I started with using DAO Star Finder to produce the source list that astrometry.net uses to find a solution, and am now using Source Extractor to see how the solution varies. I find agreement between the solutions, but when I use the DAO SF-produced list (~1000 sources total), the corr file lists ~500 matches it found to stars in the G2 catalogue. When I use the SExtr-produced list (~100,000 sources total), the corr file lists ~70 matches it found to stars in the Tycho catalogue. I just want to know why it chooses a different catalogue to find the solution for the same field? Is there a way I can specify which catalogue to use? I'm working on a photometric solution to these plates as well, and it would be nice to be able to do a one-to-one comparison between DAO SF and SExtr, but I can't do that currently because the DAO SF corr file lists G, BP, and RP mags, while the SExtr corr file lists BT and VT mags. Any guidance you can provide would be greatly appreciated! Thanks so much!

Best,

Katie

[Dustin Lang]

Hi,

There isn't an easy way to force it to use, say, only the Gaia catalogs - any index files listed in the astrometry.cfg file will be searched, (as long as it contains features that could possibly appear in your image given the --scale-low, --scale-high limits you give it).  So if you want to force Gaia, one option is to create a different astrometry.cfg file that only lists the Gaia index files - and use that config file via "solve-field --config Gaia-only.cfg ....".

Another thing you might want to try is:

- run solve-field normally

- run it again, passing in the first-round WCS file like "solve-field --verify IMAGE.wcs ....".  This will do a quick "verification" check of the first-round WCS against each index file in turn, and it will keep the highest log-odds (best match) it finds.  This can give you a lot more matches.

cheers,

dustin

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[Katie Breeland-Newcomb]

Hi Dustin,

Thank you so much for your very helpful response! I am currently in the process of building my own index files based on the Gaia catalogue for the region I am trying to solve. I tried a few different ways to convert the catalogue to a binary table, and ultimately decided to use the test2fits function, which seemed like it ran successfully. Unfortunately, when I tried to run the build-astrometry-index function with the output of the text2fits function, I got the following error:

"Reading G2RefCat_1240_bintable.fits...

Got 18940 stars
Sweep 1: 0 stars
Sweep 2: 0 stars
Sweep 3: 0 stars
Sweep 4: 0 stars
Sweep 5: 0 stars
Sweep 6: 0 stars
Sweep 7: 0 stars
Sweep 8: 0 stars
Sweep 9: 0 stars
Sweep 10: 0 stars
Total: 0 stars
Writing output...
fitstable.c:972:read_array_into: Failed to read column from FITS file
startree.c:148:startree_build: Failed to read RA from column RA
build-index.c:519:build_index: Failed to create star kdtree"

I have tried using the hpsplit function with the text2fits output, which also seemed to run fine, but when I took that output and put it into the build-astrometry-index function, I still get the same error. Any help or advice at all would be greatly appreciated!

Thanks!

Katie

[Dustin Lang]

Hi Katie,

Can you please send the command you are running, and what columns you end up with in your bintable file -- eg,

liststruc G2RefCat_1240_bintable.fits

If you've got a small region, you probably don't need to use hpsplit.

cheers,

dustin

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[Katie Breeland-Newcomb]

Sure! I am running the following command:

build-astrometry-index -i G2RefCat_1240_bintable.fits -o myindex-G2-1240.fits -P 8 -S G -H 0 -s 1 -E -I 1932011802

And the output of the command 'liststruc G2RefCat_1240_bintable.fits' is as follows:

HDU #1  Array:  NAXIS = 0,  BITPIX = 8

HDU #2  Binary Table:  3 columns x 18940 rows

 COL NAME             FORMAT

   1 RA               1E              

   2 DEC              1E              

   3 G                1E

Thanks!

[Dustin Lang]

Hi,

The "-H 0 -s 1" selects the level-1 healpix #0 -- here's the map -- https://github.com/dstndstn/astrometry.net/blob/main/util/hp.png

Maybe your catalog doesn't overlap that healpix?

cheers,

dustin

To view this discussion visit https://groups.google.com/d/msgid/astrometry/484732c4-883c-4714-a588-932d14fd40b7n%40googlegroups.com.