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PHD2 adds multi-star guiding...

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#26 StephenW

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Posted 02 December 2020 - 11:31 PM

May just be a coincidence, but even though conditions are pretty bad tonight, I'm currently getting some of my best guiding numbers with multi-star enabled...

 

Will know tomorrow morning what impact (if any) it's really had on final stars, but so far it's looking pretty good

 

phd2_multi_star_guiding.jpg


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#27 Jim Waters

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Posted 02 December 2020 - 11:45 PM

You are tracking pixels.  Do you have any idea what the arc-sec are?  What's your guide time interval?  Looking forward to your follow up tomorrow.



#28 StephenW

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Posted 02 December 2020 - 11:59 PM

>You are tracking pixels.  Do you have any idea what the arc-sec are?

 

???   I'm not "tracking pixels" - you can see in the image I attached what the RMS values are in both pixels and arc/s:  Total RMS in arc/s in the screen grab I attached: 0.52"

 

And actually right now it's currently running at 0.44" total RMS, which is literally the best I've ever seen it, and again, this is on a night of not the best seeing conditions...



#29 imtl

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Posted 03 December 2020 - 12:12 AM

Stephen this looks awesome. Now that its summer time here I'm suffering often from mediocre to bad seeing. This looks really promising. On good seeing nights I get 0.4-0.5" rms. If I can get that also on bad nights oh man what a treat!



#30 jerahian

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Posted 03 December 2020 - 12:24 AM

Well, I'm definitely seeing improvement in my guiding with the multi-star functionality.  I used to get around 0.45-.6" RMS with the latest release build, but now I'm seeing 0.3-0.35" RMS with the multi-star functionality.  This is with 3.0s guiding exposures.

 

I just did the following test:  Two 1200s exposures of the Bubble Nebula in Ha, first with multi-star enabled, and the second with multi-star disabled.

 

The resulting guiding of the first exposure with multi-star enabled is 0.35" at 200 guide frames, with a low of 0.29" at 50 guide frames.  Here is the 200 frame guiding for it:

 

multi-star_guiding.jpg

 

 

The resulting guiding of my second exposure with multi-star disabled is 0.61" at 200 guide frames, with a low of 0.48" at 50 frames.  Here is the 200 frame guiding for it:

 

one-star_guiding-200dp.jpg

 

The HFR, as measured with NINA, was 2.68 and 2.71 for the first and second subs, respectively.  I'm not surprised the HFRs are close given the 20 minute exposures.  I'm running the same test now with 600s exposures.

 

CS, Ara


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#31 imtl

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Posted 03 December 2020 - 12:33 AM

You all and your clear skies tonight. You just had to do this when I have a cloudy night and cannot test it myself?!?!? Grrrr.... bangbang.gif bangbang.gif


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#32 jerahian

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Posted 03 December 2020 - 12:46 AM

For my 600s subs, the multi-star guiding RMS came in at 0.43" and the one-star guiding RMS came in at 0.82".  I agree with Stephen, it's a pretty awful night of seeing out there up here in Maine.

 

Multi-star enabled, HFR 2.82:

 

multi-star_guiding-600s.jpg

 

Multi-star disabled, HFR 3.13:

 

one-star_guiding-600s.jpg

 

I understand these are NOT multiple runs to get a good average of HFR and I'm not refocusing in between (although the temp is < 0.5 degs between the 2 subs of each test), BUT, the guiding is noticeably better.

 

I'm calling this a win for multi-star.  Peace out!

 

CS (especially to you Eyal flowerred.gif),

Ara 


Edited by jerahian, 03 December 2020 - 09:59 AM.

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#33 imtl

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Posted 03 December 2020 - 01:02 AM

Thanks for this Ara. And to Stephen again. But final verdict of course will be how the images differ.


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#34 StephenW

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Posted 03 December 2020 - 01:11 AM

Yeah, I think it's going to take testing over multiple nights and different guiding conditions to see what impact it has, but so far it's looking positive :)


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#35 RogerM

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Posted 03 December 2020 - 01:43 AM

I installed the v2.6.9dev2 and went out to do a quick test but for some reason my tablet reverted back to 2.6.9?  Now many of you are running very much quality mounts and I only have the SGP at the moment so I'm not setting my expectations that high.  What I am curious about is whether this multi-star mode would improve my guiding given that I have a guide scope/camera that has an ~ 6.45" image scale?



#36 khursh

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Posted 03 December 2020 - 01:45 AM

popcorn.gif


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#37 imtl

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Posted 03 December 2020 - 02:00 AM

I installed the v2.6.9dev2 and went out to do a quick test but for some reason my tablet reverted back to 2.6.9?  Now many of you are running very much quality mounts and I only have the SGP at the moment so I'm not setting my expectations that high.  What I am curious about is whether this multi-star mode would improve my guiding given that I have a guide scope/camera that has an ~ 6.45" image scale?

Roger, I think with that guiding scale you will see less effect due to seeing and a question to ask is whether you're actually getting much guiding with this image scale. Well that will depend on your scope image scale and what are you after. I don't see why SGP has anything to do with your guiding.


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#38 RogerM

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Posted 03 December 2020 - 02:33 AM

Roger, I think with that guiding scale you will see less effect due to seeing and a question to ask is whether you're actually getting much guiding with this image scale. Well that will depend on your scope image scale and what are you after. I don't see why SGP has anything to do with your guiding.

Sorry, I was referring to my mount (Skyguider Pro) lol.gif

 

Yes, I've been having a go at it with the poor image scale it worked fine for really wide field and I'll be switching out the guide camera soon...got my hands on an ASI290MM so at least I'll be bringing that number down to around 5 as a next step.  Scale for my imaging train is around 1.4.  You've seen what I've been able to accomplish so far on NGC1499 (thanks again for the mosaic help btw!) so it's all not a terrible loss.  I'm primarily struggling at the moment with poor seeing affecting stability (guiding error varies from 1.2" to over 1.8" RMS.)

 

My ability to carry around a more serious mount and tripod is severely limited at this time so I'm trying to make do with a highly portable arrangement for the time being.  Squeaking out as much performance from this current setup as possible so even if this multi-star guiding affords me any improvement in guiding I'll be one happy camper!


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#39 imtl

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Posted 03 December 2020 - 02:51 AM

Sorry, I was referring to my mount (Skyguider Pro) lol.gif

 

Yes, I've been having a go at it with the poor image scale it worked fine for really wide field and I'll be switching out the guide camera soon...got my hands on an ASI290MM so at least I'll be bringing that number down to around 5 as a next step.  Scale for my imaging train is around 1.4.  You've seen what I've been able to accomplish so far on NGC1499 (thanks again for the mosaic help btw!) so it's all not a terrible loss.  I'm primarily struggling at the moment with poor seeing affecting stability (guiding error varies from 1.2" to over 1.8" RMS.)

 

My ability to carry around a more serious mount and tripod is severely limited at this time so I'm trying to make do with a highly portable arrangement for the time being.  Squeaking out as much performance from this current setup as possible so even if this multi-star guiding affords me any improvement in guiding I'll be one happy camper!

Okay that makes more sense smile.gif

 

Maybe move to OAG? 

 

I think from what you're writing here then this multistar guiding is going to be good for you. Try it and see!

 

Glad the mosaic worked out smile.gif


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#40 endless-sky

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Posted 03 December 2020 - 03:15 AM

NightBear: from 0.72" to 0.4" (80% better)

jerahian: from 0.61" to 0.35" (74% better)

jerahian: from 0.82" to 0.43" (91% better)

Forward Scatter: from 1.1" (let's take the average from 1" and 1.2") to 0.7" (57% better)

 

Average improvement 75.5%.

 

I would say it's quite a success!

 

Now release the software so us poor souls stuck with Linux and a Raspberry can use it too!


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#41 imtl

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Posted 03 December 2020 - 04:53 AM

Another couple of data points for ya' all.

 

Without -> with multi stars method:

 

0.92" -> 0.6" rms. But parameters were a bit tight with too many corrections for my taste.

 

0.83" -> 0.49" rms laxing the parameters a bit and lowering the exposure to 3s to test for seeing more.

 

I actually had a couple of minutes down to 0.3"-0.35" rms.

 

Tonight's seeing is average.

 

I find that it shows more improvement with short exposure times. Which makes sense since this is really mostly to negate seeing effects. I usually keep my exposures at >=4s. But I'm working at 3s now. Looking good.


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#42 endless-sky

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Posted 03 December 2020 - 06:20 AM

Another couple of data points for ya' all.

 

Without -> with multi stars method:

 

0.92" -> 0.6" rms. But parameters were a bit tight with too many corrections for my taste.

 

0.83" -> 0.49" rms laxing the parameters a bit and lowering the exposure to 3s to test for seeing more.

 

I actually had a couple of minutes down to 0.3"-0.35" rms.

 

Tonight's seeing is average.

 

I find that it shows more improvement with short exposure times. Which makes sense since this is really mostly to negate seeing effects. I usually keep my exposures at >=4s. But I'm working at 3s now. Looking good.

Those are some nice improvements! I would say that almost halving the RMS with just a guiding algorithm is a lot better than possibly paying 2x-5x your current mount cost (to upgrade to the next step up) to obtain the same thing.

 

My NEQ6 Pro has been giving me anywhere from 0.6" to 1" total RMS since I added autoguiding to my setup, a couple of months ago. This with single star, predictive PEC and 2 to 3s exposures. I have been chasing the more consistant holy grail of 0.4-0.6" RMS and tasted it only a couple of times. But if those improvements are a good indication on what I can expect to achieve, then I think I will be drinking out of it a lot more often.

 

And, best of all, without spending a euro-cent!


Edited by endlessky, 03 December 2020 - 06:21 AM.

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#43 imtl

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Posted 03 December 2020 - 06:39 AM

Okay I did a longer run before the annoying clouds rolled in. This time I used my regular settings for guiding. The differences were smaller but still there.

 

About 0.58-0.6" rms without multi star and 0.4-0.44" rms with. These were runs of about 30 minutes each. Didn't touch anything else.

 

This is indeed very nice and could potentially help when going to higher image scales such as with SCT. For me, I have 1.13"/pixel resolution so I'm not guiding limited at all. I do not expect to see any differences in my final images but I'll take a closer look another night when the clouds are not in my way...bangbang.gif

 

What I am happy about is that my guiding parameters just work and I haven't really changed them (besides the occasional minmo) for quite a while now. If it works don't break it. But if you get a free upgrade, use it grin.gif

 

Night ya' all


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#44 spokeshave

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Posted 03 December 2020 - 08:15 AM

I tried it last night. The difference was frankly pretty astonishing. It was too windy for any meaningful test with imaging, but I did some somewhat qualitative testing between gusts since multi-star guiding has no particular advantage when dealing with wind. 

 

The idea behind multi-star guiding is that the majority of seeing effects are localized to areas on the order of arcseconds in apparent angular diameter. This means that each star that is any meaningful distance away from another star in the guide field will experience completely different seeing. Since seeing results in random displacement of star images, averaging the displacement of multiple stars will cause the displacement to add in quadrature just like noise does. PHD2 uses (up to) 9 stars for its multi-star algorithm so we can expect to see "seeing" effects reduces by a factor of the square root of 9, or 3.

 

My test was to run PHD2 unguided and observe the Declination RMS deviation for both the single star and multi-star algorithms. I selected Dec to remove tracking error as a variable. If theory holds, the RMS deviation in Dec should be about 3 times higher for single star guiding compared to multi-star guiding. I found that using single star guiding, my Dec RMS was about 0.45". Using multi-star, it was about 0.21" for a difference of a factor of 2.1. Not quite the 3 that theory predicts, but probably within the error bars of my subjective test. I say "subjective" because I had to reject data that to my eye appeared to be the result of wind gusts. I look forward to trying this on a calmer night.

 

I will say that the effect was pretty remarkable. It was literally like flipping a switch as I toggled multi-star on and off. With it on, the graph would turn to a beautiful near-flat trace, and with it off, the trace would jump around quite a bit more. As for actual guiding, I only caught glimpses between puffs of wind, but during particularly gentle times, I saw patches with each axis less than 0.3" RMS and Dec often dropping below 0.2". My typical guiding performance is around 0.5" per axis, so that is a dramatic improvement.

 

One thing I did notice is that the multi-star algorithm reduced seeing effects enough to reveal the roughness in my mount's RA tracking. There would be times for minutes on end between gusts where Dec would be below 0.2" RMS, and even periods when it dropped below 0.1" for meaningful periods of time. But my RA seldom dropped below 0.25". So it appears that my mount is just not capable of tracking in RA below 0.25" RMS. That's not a complaint, just an observation. Tracking at 0.25" RMS is actually pretty remarkable. 

 

Anyway, my preliminary thoughts are that multi-star guiding is a huge step forward for guiding.

 

Tim


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#45 StephenW

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Posted 03 December 2020 - 10:20 AM

Unfortunately the weather did not cooperate for me last night - I let my imaging session run but had multiple star-loss events and eventually was clouded out.

 

I did have one good 1+ hour run with RA at 0.39" and DEC at 0.30", total RMS at 0.49".    For my local conditions, this is the best I've seen.

 

Definitely looking forward to seeing how it performs over the coming weeks.

 

phd2_multi_star_guiding_2.jpg



#46 endless-sky

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Posted 03 December 2020 - 10:26 AM

Anyone knows how to build the PHD2 Dev version on a Raspberry?

 

I can't wait to try it out, but it usually takes ages for these things to be included in the self-updating packages (like Astroberry, which I am using). I am also waiting on the newer KStars/EKOS version, but the developer has not add it to Astroberry, yet.

 

If anyone knows how to build these things manually, I would appreciate it!



#47 fewayne

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Posted 03 December 2020 - 10:56 AM

Average improvement 75.5%.

 

I would say it's quite a success!

 

Now release the software so us poor souls stuck with Linux and a Raspberry can use it too!

Agreed, this is pretty exciting. BTW I may do software for a living but I'm a Programmer of Very Little Brain. I downloaded the source for PHD and built it on my Pi and it was pretty much a no-....well, a very-little-brainer, at least. It winds up taking a fair amount of space but the instructions are clear and It Just Worked, at least for me with StellarMate OS. Once I had the executable built I could just run it, there wasn't any weird black installation magic.

 

ETA: Gaaa, I just saw your other comment just above mine! Will put together something posthaste.


Edited by fewayne, 03 December 2020 - 10:57 AM.


#48 fewayne

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Posted 03 December 2020 - 11:03 AM

Here are the build-from-source instructions: https://github.com/O...dingPHD2OnLinux

 

Those instructions presume that you have git (the source control system, if you're unfamiliar) installed. If not, you can download a ZIP of the source from the GitHub page and go from there: https://github.com/OpenPHDGuiding/phd2

 

If you're not sure which set of instructions to follow, try uname -a on a command line and see what sort of system you have.


Edited by fewayne, 03 December 2020 - 11:09 AM.


#49 endless-sky

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Posted 03 December 2020 - 11:11 AM

Agreed, this is pretty exciting. BTW I may do software for a living but I'm a Programmer of Very Little Brain. I downloaded the source for PHD and built it on my Pi and it was pretty much a no-....well, a very-little-brainer, at least. It winds up taking a fair amount of space but the instructions are clear and It Just Worked, at least for me with StellarMate OS. Once I had the executable built I could just run it, there wasn't any weird black installation magic.

 

ETA: Gaaa, I just saw your other comment just above mine! Will put together something posthaste.

 

Here are the build-from-source instructions: https://github.com/O...dingPHD2OnLinux

 

Those instructions presume that you have git (the source control system, if you're unfamiliar) installed. If not, you can download a ZIP of the source from the GitHub page and go from there: https://github.com/OpenPHDGuiding/phd2

Thank you for the instructions! I will definitely give it a try.

 

Question: I assume that doing it this way, then I'll end up with two different PHD2 in my Astroberry, correct? The one that's already installed (stable 2.6.9), plus the one I built using the instructions above.

 

Whenever the maintainer of Astroberry will release the new updates (installable with the classic "sudo apt update" and "sudo apt upgrade"), will I be able to remove/uninstall the one I built (so that I don't have two PHD2 with the same version)? If so, how?

 

Thanks again, but I literally have zero knowledge about Linux/Raspbian/Ubuntu other than the very basic commands.


Edited by endlessky, 03 December 2020 - 11:21 AM.


#50 endless-sky

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Posted 03 December 2020 - 11:57 AM

Well, I just finished building it. For some reason, running ./phd2 like the guide said, opened up the regular PHD2 (2.6.9) that's already installed.

 

So, I went ahead and run "sudo make install" - now when I run PHD2 (whether with the ./phd2 command or by the icon I have always been using), the newer version starts: 2.6.9dev2. I guess I successfully overwrote (or, rather, updated) the existing PHD2.

 

To free up some space, I assume I can delete the "phd2" folder created by git along with all its contents. Right? confused1.gif

 

EDIT: just to confirm everything worked fine! I fired up the Simulator profile both in EKOS and in my newly built PHD2 and everything works. Even the multi-star option. First clear night available I am going to give it a try. I guess I could update KStars/EKOS in the same way - by building it from source and then running "sudo make install". Now I don't have to wait on developers anymore... grin.gif lol.gif


Edited by endlessky, 03 December 2020 - 12:05 PM.

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