New Feature : SharpSolve - SharpCap's new built-in plate solver

All the latest news about new features and improvements to SharpCap
User avatar
admin
Site Admin
Posts: 12424
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

New Feature : SharpSolve - SharpCap's new built-in plate solver

#1

Post by admin »

I'm really excited to be able to announce this new feature!

Having plate solving built into SharpCap without needing a separate program to be installed and configured will make it easily available to far wider range of people. For those already using Astrotortilla or Astap, you might well find that SharpSolve is quicker and works in a more seamless manner :)

I've been thinking about whether I could turn the code used for Polar Alignment into a full plate solving engine for a while, but other than jot down a few notes I deliberately held off doing anything about it until the update of the user manual for SharpCap 4.1 was complete. It was something to look forward to once the documentation work was done!

I needed to sort out a number of problems with the way the polar alignment code worked to make SharpSolve a possibility, including...
  • Speed - polar alignment is fast at solving, but only checks an area of less than 0.5% of the total sky - taking 200 times longer wouldn't be quick enough
  • Size of star data - storing the star data in the same way as used for polar alignment would mean that the star data alone would be over 300Mb - twice as big as all of the rest of SharpCap!
  • Being sure of a correct match - polar alignment rarely brings up a false positive match, but they can happen now and then. With 200 times as many stars to match, that needed fixing to avoid issues
  • Reliability - I needed to be confident that SharpSolve will really find plate solving solutions for sky images with a very low failure rate
I have been working on this pretty much full time for the last 3 weeks or so, which has meant that apart from bug fixes not much else has happend to SharpCap in that time. I believe that I have now succeeded in meeting my goals, so I have included SharpSolve in today's SharpCap 4.1 update (4.1.11226).

How to start using SharpSolve

Go to the Plate Solving settings and choose 'SharpSolve' from the list of plate solving tools. Note that it will be the default on new installations of SharpCap, but if you have previously used SharpCap then the existing selection will be retained.
Screenshot 2023-10-30 151657.jpg
Screenshot 2023-10-30 151657.jpg (71.44 KiB) Viewed 3421 times
There are no options that need adjusting when using SharpSolve (at least none yet), but do note that it works best when it can detect 60 to 100 stars in the image, so set your gain/exposure appropriately. SharpSolve *will* find stars that are only visible when the image from the camera is stretched.

What fields of view does it handle?

SharpSolve can solve when the smaller dimension of the image is between 0.5 and 7 degrees. You may have reasonable success rates solving down to about 0.4 by 0.4 degrees, but it is unlikely to work for smaller fields of view than that. This means that for long focal lengths (2000mm or more) you will need a relatively big imaging sensor (IMX571 or APSC size or larger). However, more modest cameras will work well at more reasonable focal lengths of 1000mm or less.

How fast is it?

My testing has shown SharpSolve to be faster than other plate solving tools - on my fast desktop PC it will use up to 4 CPU cores and do a complete sky search for all scales down to 0.5° in about 9 seconds. On the same PC, Astap takes over a minute for a full sky search at 0.5°, with additional time taken for other image scales.

SharpSolve will use up to half of your CPU cores (maximum of 4, limited to half to make sure it doesn't cause the whole PC to grind to a halt), but even on a single CPU core a full sky search should be around 1 minute on a typical recent CPU or 1-2 minutes on a slower CPU with the exception of very low power ones. Searching a limited area of sky is much faster.

SharpSolve has an advantage over the other plate solving tools in that all the work is done inside SharpCap. When using Astap, Astrotortilla, etc, SharpCap has to write the image to a file on disk which the other application then needs to read, slowing things down.

How reliable is it?

I used a rare clear night to setup the SharpCap sequencer to do a 'sky scan' of part of the sky - capturing a 10s image, moving 2.5 degrees, capturing another image and so on. Over a few hours I ended up with 300 images of a chunk of the northern sky between Dec=0 and Dec=45. Each image is 3.9x2.6 degrees. All of those images solve.

I then wrote code to cut up these images into sub-areas and try to solve those. A sub-area of 1200x800 pixels corresponds to 0.75x0.5 degrees. Out of 167700 sub-areas tested, only 22 that have at least 25 stars detected in the sub-area fail to solve (less than 25 stars is considered to be too low for reliability, although sometimes you can solve at about 15 stars). This is a success rate of about 99.99%

Moving to a 800x800 pixel sub-area - 0.5° by 0.5° - the success rate drops to about 99.2%. Although I can make changes to improve this success rate, I have been unable to do so without a significant increase in the amount of star data needed and a similar slowdown in the solving procedure.

How accurate is it?

To within a few arc-seconds - in most cases probably no more than 1 to 2 arc seconds of error. SharpSolve does not aim to produce high accuracy (sub-arc second accurate) results - it is aimed at speed and having a relatively small star database. Note that the star database used by SharpSolve only stores star positions accurate to about 1 arc second to reduce database size.

Note that SharpSolve can track position correctly across the frame, even near the celestial poles where the lines of declination are curved and the lines of RA converge on the pole. This means that deep sky annotation positions and co-ordinate readouts will be far more accurate near the pole when using SharpSolve

How likely are false positives?

This one is easy to test - you make a set of 100 random star positions and see if you get a solution. If you do, it's a false positive, if not then you keep repeating to see how many times you can do this before you *do* get a false positive. I ran 3000 repetitions of an entire sky search on random stars without any false positives. That suggests that the rate is below 1 in 1000 and probably a lot lower.


Well, that's probably enough info to get people started. Please try it out and let me know if it works (or how you broke it!).

cheers,

Robin
StarFlea
Posts: 54
Joined: Wed Dec 21, 2022 12:22 pm

Re: New Feature : SharpSolve - SharpCap's new built-in plate solver

#2

Post by StarFlea »

Hi Robin!

That sounds very interesting! Is this a blind solver?

I'll try this out at the next opportunity (if the weather is good again)...

A huge wishful feature that builds on this would be a three-point polar alignment in the next step (similar to what is found in NINA). This would make it possible to achieve good polar alignment with SharpCap even without a view of Polaris...

THX for this feature! :)

StarFlea
User avatar
admin
Site Admin
Posts: 12424
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: New Feature : SharpSolve - SharpCap's new built-in plate solver

#3

Post by admin »

Hi,

yes, SharpSolve is capable of blind plate solving - on a fast PC, a full sky search can be as quick as 8 seconds (in practice even quicker, as SharpCap will choose the zenith as the starting point if it knows your latitude/longitude, meaning if you are actually imaging the real sky it only has to search a maximum of half of the total celestial sphere before getting to the right place).

Certainly this makes it easier to build in more features based on plate solving as there will now always be plate solving available rather than relying on the end user to install Astap or Astrotortilla. I don't trust GOTO based polar alignment routines as any errors in the GOTO movements feed through into the final result, but a routine based on slewing the RA axis only to several points in RA and plate solving should be workable.

cheers,

Robin
User avatar
carlomuccini
Posts: 108
Joined: Mon Apr 27, 2020 12:42 pm
Location: Montecatini Terme (PT), Italy
Contact:

Re: New Feature : SharpSolve - SharpCap's new built-in plate solver

#4

Post by carlomuccini »

Thanks for this new version, it is immediate andis very fast in plate solving.
I tested the program in TEST CAMERA mode using different images taken with different telescopes and cameras and it always resolved correctly very quickly
Focal lengths from 300mm to 980mm with ASI294MM and ASI533MC always perfect and much much faster than ASTAP.

Thanks for this great feature!

Carlo
User avatar
admin
Site Admin
Posts: 12424
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: New Feature : SharpSolve - SharpCap's new built-in plate solver

#5

Post by admin »

Hi Carlo,

I have to own up here and admit that when you use the test camera (or the Folder Monitor Camera), SharpCap will read FITS header info and use the co-ordinates found in the header as the starting point for any plate solve operation if a mount is not connected. That means that plate solve operations of previously saved FITS files are likely to be quick with any plate solving tool. If you try a PNG or TIFF of the same image then you will see a more representative speed of a whole sky search.

I am currently thinking that there is a bit of a problem caused by how many update notifications on the search progress are being displayed (and saved in the log), so I am going to limit the rate of those updates.

cheers,

Robin
Harmonious
Posts: 40
Joined: Tue Nov 28, 2017 11:20 pm

Re: New Feature : SharpSolve - SharpCap's new built-in plate solver

#6

Post by Harmonious »

I installed the update last night and gave it try using a 120mm f/7 refractor and a Player One camera with the IMX571 sensor. The PC has a Ryzen 7 5700G CPU (8 cores, 16 processors) and 32GB of memory. SharpSolve seemed at least as fast as ASTAP and with gain = zero worked at exposures as low as 1 second. At one second it had one initial failure but succeeded on the second try.

I noticed that you did have "Do not use" selected under Focal length of telescope. Would there be any reason to use the focal length as I do when using ASTAP?
User avatar
admin
Site Admin
Posts: 12424
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: New Feature : SharpSolve - SharpCap's new built-in plate solver

#7

Post by admin »

Hi,

thanks for the positive report :)

If your field of view is above 1x1 degrees then you will get a speed up by specifying the focal length, as it allows SharpCap to skip building and checking the parts of the plate solving index related to smaller scales. Unlike Astap, SharpSolve doesn't try each size of image separately, instead it does everything down to the minimum size in one go. By setting the FOV you can lift the minimum size.

cheers,

Robin
MarMax
Posts: 94
Joined: Sun Sep 19, 2021 11:43 pm

Re: New Feature : SharpSolve - SharpCap's new built-in plate solver

#8

Post by MarMax »

Robin,

This sounds like a great addition to SharpCap. I use the C11 at f/6.1 (170mm) and f/10 (2800mm) and have a 72mm f/6 guide scope with a 462MM camera. Some times I need to switch to the guide camera when an ASTAP plate solve fails at the longer focal lengths. The part of this that is most tedious is going in and changing the focal length of telescope.

It sounds like this setting is not necessary with SharpSolve. Is this correct?

Mike
User avatar
admin
Site Admin
Posts: 12424
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: New Feature : SharpSolve - SharpCap's new built-in plate solver

#9

Post by admin »

Hi Mike,

yes, the focal length setting is non-critical and while it gives a speed up, if solving is only taking seconds without setting the focal length then it's not really worth setting it.

You will need an APS-C size camera (IMX571 or similar) if you are using 1700mm focal length, and probably a full frame camera at 2800mm if you are going to be above the 0.5 degree in each direction minimum frame size limit though.

cheers,

Robin
User avatar
admin
Site Admin
Posts: 12424
Joined: Sat Feb 11, 2017 3:52 pm
Location: Vale of the White Horse, UK
Contact:

Re: New Feature : SharpSolve - SharpCap's new built-in plate solver

#10

Post by admin »

I have just put an even newer update - 4.1.11239 online.

There was a bug I had accidentally added in 4.1.11226 that caused a crash when plate solving if certain plate solving options were set. It wan't until I'd got 3 or 4 bug reports of the same problem that I managed to spot how and why the problem was happening :(

I also took the opportunity to tweak SharpSolve to limit the rate at which it shows 'Searching at...' notifications and fix an issue where some of the 'Searching at...' notifications could appear after the 'Plate solve success' notification. I have also ensured that you can't get it to start a new attempt at plate solving while the previous attempt is still running.

I'm looking into the possibility of a downloadable extended plate solving index that would take the minimum field of view down to 0.33 degrees or maybe even 0.25 degrees. To get that to work though you need to start with a pretty enormous star catalog. The current index is build from the UCAC4 catalog of about 114,000,000 stars. In some of the sparser regions of the sky, the UCAC4 data doesn't contain as many stars per square degree as I would like to have to ensure good coverage. Note that I don't put all the stars into the index, or even all the stars down to a particular magnitude - the index is built to have a roughly constant density of stars per square degree across the whole sky, so in the richer areas of the milky way, the dimmest included stars might be magnitude 11 to 14 where in the sparse areas stars will be included at magnitude 15, 16 or beyond.

I now have 27Gb of data containing 428,000,000 stars to play with, but it is in a slightly different format :) All good fun!

cheers,

Robin
Post Reply