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INDI Library v2.0.6 is Released (02 Feb 2024)

Bi-monthly release with minor bug fixes and improvements

Re:New Polar Alignment Scheme and Features

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Sorry, but your plot has several errors. Then math doesn't help. But I'm out here now....
3 years 2 months ago #66208
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With the close to pole alignment, I was asked to slew 89260.7 degrees in RA then 279141 degrees. I slewed manually a sensible amount and the magnitude of the PAE reported looked about right. I didn't check the orientation though.
Log attached

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File Name: Closetopolealign.log
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3 years 2 months ago #66209
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Just as well I have an M-Uno with a slip ring. I could rotate 1 million degrees if I had to :)
3 years 2 months ago #66210
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A million degrees! That's crazy. I checked the code but nothing stands out. It just takes whatever degree you put in the spin box. English is the current locale, right?

Regarding the motion itself, you don't to worry about alignment, the mount is commanded WEST/EAST directly, not via GOTO, so no chances of DEC playing a role here.
3 years 2 months ago #66221
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Hi Jasem
I was using the manual slew option. The spin box had whatever was the default but obviously is not used for manual slewing.
With the near pole method it asked me to slew 89,260.7 degrees. At first I thought it was using European decimal notation till I saw the ".7" .
Locale is English, specifically LANG=C.UTF-8
3 years 2 months ago #66222
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FYI, I submitted a fix to the Polar Alignment Assistant (PAA) for an issue related to the rendering of the correction triangle. This fix is detailed in  invent.kde.org/education/kstars/-/merge_requests/198 and has already been merged into the KStars source code, though as I write this is not yet in any nightlies. This will likely fix the triangle-rendering issue reported by @rbarberac and also by Jasem. I'm hoping my fix from last week solved the east/west issue reported by @rugbyrene (and seconded by Jasem). Assuming these are indeed fixed, I'm not aware of other issues with the new PAA code (Jasem is looking at the "manual issue" brought up by @kengs).

While I was testing that fix, I ran polar alignment using my telescope 18 times over the course of an hour in several different ways:
  • rotating East, starting by pointing near the northern pole,
  • rotating West, starting by pointing near the northern pole,
  • rotating East, starting East of the meridian at about DEC=60
  • rotating West, starting West of the meridian at about DEC=60
All my tests went well.

I have a couple things to mention, not directly related to my changes:
  • I once got a "Solver Failed" during PAA, and when that happens, the system doesn't gracefully retry. You need to stop the PAA process, and restart it. I'd like to correct that, but it may not be right away, as I want to make sure this system works, and this state machine can be tricky.
  • I noticed that my system started up with 8x mount speed. Perhaps that was due to some debugging I was doing previously, but if you notice the slew going very very slowly, check that menu item on the polar-alignment tab.
  • I removed the "flip the correction vector" option. I don't think it makes sense any longer, and would confuse the interface. If you feel you need to reverse the correction vector, please contact me and I will try and fix the underlying issue.
Please let me know if you see any further issues.
The following user(s) said Thank You: Rafa Barberá
3 years 2 months ago #66253
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I did have some clear sky down at sealevel last night, so I decided I have a try using the new PA with my Star Adventurer and the ASI183MC with an Canon 135mm lens.
The sky view from my terrace is hugely limited, basically only ENE to SSW and up to zenith :ohmy: But enough for testing PA.

I had to use the telescope simulator, as the mount doesn't have any connection to the computer, and switch off position hinting for the solver. Amazingly, even with only image scale limits it was blazing fast, solving in a second or so. But without a compass or view to polaris, my initial orientation was largely off.
Without mount control/info I had to use the 'manual slew' option, and hand-turn the SA to various positions.
As it was the first time using refresh/move it took me three tries before I touched the Alt/Az knobs, and re-did the measurement a few times with different pointing positions. The nice outcome was that the determined PAE was quite consistent - though at 17 degrees.... It took me several additional rounds of measure-align, including repositioning the tripod because I hit the alignment limits of the mount. I eventually got the error down to 15'. Trying better was somewhat futile, due to the (in)stability of the photo tripod I used. But all in all a very pleasant experience :cheer:

One thing I noticed was that - especially for the large error - the movement direction of the star when tuning the mount orientation did not really match the guide lines plotted. So I wondered if there might be still some (small) error in the coordinate conversion that shows up at larger offsets. However, while writing this, I realized that I had used the observation coordinates of the observatory, some 30km away from here. Would that affect things? In principle I'd say no, as you can PA without knowing where you are?

So if weather cooperates I'll try that again tonight, with proper location and the new code. Because of course as soon as I had finished PA last night the clouds rolled over again... :sick:
I didn't have debug on, so I assume the logfile isn't too helpful..

Cheers,

Pit
3 years 2 months ago #66270
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Pit,

Thanks for the challenging test!

Re the lines not matching the star movement, my guess is this: You have a huge error, 17 degrees. I implemented drawing a straight line in image space (2D projection of the actual 3D curve) between the start point and the solution point. This projection is likely fine for most use cases, but when your error is that large, the projection probably doesn't match the geodesic as well as you'd like. You're the expert in this kind of math, so let me know if you disagree.

I'd expect that this isn't a problem as (a) it led to the solution iteratively anyway, and (b) with a compass and an astro setup, most folks should start much closer to the solution, even with that poor a view of the night sky.

If there was good reason, I could switch from a single projected line, to a series of line segments that better match the geodesic, but I think that would be overkill for almost all use cases. Again, let me know what you think.

Hy
3 years 2 months ago #66287
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Hy,

I managed to get out last night and test out the PA routine. I was able to really dial in my PA like never before so thank you! And with GPG enabled I got sub-arc second guiding. I’ve never had that before.

I do have an enhancement suggestion. Would it be possible for the display to auto zoom once you get within a certain pre-defined PA error? It would work similar to what is implemented in the iOptron iPolar software, where as you are making adjustments it will present a zoomed in sub-window which allows you to make even finer adjustments. I realise we can manually zoom but it requires us to stop making adjustments, zoom in, pan around to find the adjustment vectors and return to making adjustment.

It’s a little thing that would make the process easier.

Rene
3 years 2 months ago #66372
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Sorry for the silence. No news here, the clouds are back, and the road to up above the clouds is closed due to landslides :ohmy:

Your explanation of the deviation seems very sound! I agree that the test was really a challenge, especially as my compass is in the observatory, and not here :P . But such extreme settings often help to pinpoint problems.
I absolutely agree that it's not really needed to change the plotting. If one gets such large corrections an iteration is needed anyhow, and that one will have better matched movement paths. So all fine for now. I'll pester you again once I find more silly ideas ;)
3 years 2 months ago #66374
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While testing some new polar alignment code this evening, I came across an interesting screenshot I wanted to share.

I positioned the telescope to point just North of the Equator, and just West of the Meridian (and I'm in the Northern Hemisphere).
I ran polar alignment with two 30-degree slews going West. I had intentionally messed up my polar alignment by about 1/2 degree.
Looking at the log, spot of the 3rd PAA image is azimuth 253.934 altitude 23.5716.




What I wanted to point out, is that the correction triangle is telling the user to use the altitude knob to move the star along the yellow line seemingly AWAY from the ultimate target. When the user reaches the end of the yellow line, then adjusting the azimuth knob would bring the star along the green line to the target. It turns out that there are spots in the sky where azimuth and altitude corrections at the pole map to surprising directions like this. This is the reason I originally came up with the idea of introducing a correction triangle.

In fact, I followed the directions given, and the resulting correction worked fine. I verified this by re-checking polar alignment at the pole.
Hy
The following user(s) said Thank You: Jasem Mutlaq, Ken Self, Jim, Brian, Peter Sütterlin
3 years 2 months ago #66502
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Bravo Hy! Great work on the PAA tool! I wonder if this could be remotely related to why the direction for the correction vector was reversed for some users before you introduced the triangle?
3 years 2 months ago #66512
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