Plate solving with Astrotortilla

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Ukjay1971
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Joined: Fri Mar 03, 2017 3:09 pm

Plate solving with Astrotortilla

#1

Post by Ukjay1971 »

Which profile is used in Astrotortilla if platesolving from Sharpcap? I assume it loads the default Astrotortilla.cfg? If so, then that might be why some people who have created specific profiles can't plate solve.
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admin
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Re: Plate solving with Astrotortilla

#2

Post by admin »

Ah, SharpCap doesn't use any of the AstroTortilla profiles - it just treats AstroTortilla (and AnSvr or AllSkyPlateSolver) as a handy way of getting the plate solving engine and the databases installed and then uses the astrometry.net solver direction (the solve-field command line application).

The parameters used are

Code: Select all

solve-field -b /etc/astrometry/backend.cfg  --ra {approxPosition.RightAscension*15} --dec {approxPosition.Declination} --radius 15 --sigma 50 -r --objs 100 --no-plots -N none -L 0.1 -H 20 -u degwidth -D {cygTmpFolder} {cygTmpFolder}/frame.png
I suspect that the only number that you might want to change here is the --sigma value, but I'd be interested to hear what other settings people have to use in AstroTortilla to get working solutions if they are having problems in SharpCap.

cheers,

Robin
robrj
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Joined: Fri Feb 17, 2017 1:03 am

Re: Plate solving with Astrotortilla

#3

Post by robrj »

When I use Astrotortilla (not with Sharpcap yet), if I'm not getting enough results, I usually wind up adjusting the Sigma value depending on how many objects it finds. You typically need 40 or more results for it to solve. The sigma is lowered to get more results with a minimum value of 20. With a 10s exposure setting in Astrotortilla, I usually don't have to adjust it as much with the default setting of 70.

The -L and -H parameters are different as well. For the fastest solves, you want those parameters as close as possible to your minimum and maximum field of view of your telescope in degrees (round up to one decimal place for H and round down to 1 decimal place for L). The setting in the example code above is showing a minimum of .1° to 20°which is very wide.

For example, with my ED80T-CF and the ZWO ASI185MC, I get a field of view of 52.21' x 32.87'. Divide each by 60 to get into degrees and I get 0.87° x 0.55°. I want to bracket the view so I round up for the large one and down for the smaller one (0.9°x 0.5°)
So in Astrotortilla, I set the H and L values as follows: -L 0.5 (rounded down from the minimum) -H 0.9 (rounded up from the maximum)

In the Orion Skyview Pro 8" newtonian and the ZWO ASI185MC, I get a field of view of 25.06' x 15.78'. Dividing each by 60 to get degrees yields 0.42°x 0.26°

So in Astrotortilla, I set the H and L values as follows: -L 0.2 -H 0.5

I could probably set -L 0.2 and -H 0.9 to cover both scopes with one setting, although I think it increases the plate solve time a bit. I have separate equipment profiles set up so I just change them as needed.

This page has a tutorial on setting up Astrotortilla. It shows what the parameters are for and how to set it up to match your system:
http://www.lightvortexastronomy.com/tut ... lving.html
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Re: Plate solving with Astrotortilla

#4

Post by admin »

Yes, if I knew the scale then I could improve the speed by limiting -L and -H, but actually the "--radius 15" parameter which means it only searches within 15 degrees of the current pointing gives decent solution speed even with the wide range of scales.

cheers,

Robin
robrj
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Re: Plate solving with Astrotortilla

#5

Post by robrj »

Is that bit of code editable by the end user (e.g., how would he change the sigma)?
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Re: Plate solving with Astrotortilla

#6

Post by admin »

Not yet, no - one for the todo list.

cheers,

Robin
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