iPolar Alignment doesn't match PHD2 Drift alignment

[JonCarleton]

I bought a new GEM28 iOptron mount earlier this year.  It seems to work pretty well and I don't notice any specific mechanical issues.  However, guiding with PHP2 has been less than spectacular.  Along with that, sometimes it is pretty good and other times pretty awful.  Sometimes a target at one end of the sky works well and another later that same evening just doesn't.

The polar alignment is being done with the iPolar "Windoze" program connected to the in-mount iPolar scope.  This, by itself is a sore spot, because I had to buy a little Windoze box to run the !@#$ iPolar program.  The sole Windoze box in my "collection."  I plug it in, do the polar align, then unplug it and put it away in a box in the closet and proceed happily in Linux.  I know that the iPolar camera will operate marginally with a V4L2 Linux driver, and I could use a Linux program, but given I believed the problem was alignment, I have been trying to limit the variables.  And the Windoze/iPolar solution was "the factory recommendation."

But, I digress.  A few nights ago, I spent quite a lot of time with PHD2 Guiding Assistant, trying desperately to get a guiding plot that didn't look like a wave of tsunamis.  I couldn't help notice that, though iPolar results were rock solid and spot on for polar alignment, PHD2 Guiding Assistant was reporting a very significant polar alignment error (400+/- arc-min).  So, I did a Drift Alignment in PHD2.  The Azimuth was pretty much on target, but the Altitude was very significantly off.  In the end, after the Drift Alignment, I was able to get fair guiding (not wonderful, but fair enough to image).  Later I checked alignment with iPolar, which reported, to no great surprise, that the Altitude setting was in need of significant adjustment.

I need more testing to be certain, but I am thinking that since I guide with PHD2, I should use its Drift Alignment and chuck the iPolar regimen.  The problem is the mystery.  I don't care much for mystery.  Is it possible that the factory-mounted internal iPolar mount camera could be misaligned?  Is that even possible?  Or is there something else going on that I haven't considered?  The latter is always a reasonable possibility.

The setup is a fairly straight-forward all-stock GEM-28 with mount on the stock tripod on a solid foundation with a Radian Raptor and a SVBony 30mm guide scope.  Linux Ubuntu 20.04 on a Pi4 8G with INDI server for the mount, cameras and focuser.  PHD2 running local on the Linux box that runs the INDI server.  Just as a FYI, I did do a guiding session using that little Windoze box with ASCOM drivers and PHD2 Windoze version as a test some weeks ago.  The results were similar if not worse, though I admit to some bias in that opinion.

Thoughts?

Edited December 3, 2021 by JonCarleton

[jjosefsen]

You can do a PA routine similar to that of the iPolar (plate solved PA) using your guidescope and camera and PHD2, which would let you ditch the windows pc.

In terms of why it is differing, are there perhaps any location settings that are off somewhere? Either mount (INDI/ASCOM) or in the iPolar application?

That is almost the only thing I can think of.

Edited December 3, 2021 by jjosefsen

[JonCarleton]

12 minutes ago, jjosefsen said:

You can do a PA routine similar to that of the iPolar (plate solved PA) using your guidescope and camera and PHD2, which would let you ditch the windows pc.

In terms of why it is differing, are there perhaps any location settings that are off somewhere? Either mount (INDI/ASCOM) or in the iPolar application?

That is almost the only thing I can think of.

Thanks for your reply.  I'm a pilot, and accurate lat/lons are part of my "religion."  I will check them again to be sure, but I don't think that is the issue.  I would suspect my Plate Solving would get wonky if the location settings were off, and Plate Solving has been excellent.  I have several options for polar alignment other than the iPolar regimen.  PHD2 has several and there is a pretty good routine in CCDCiel, that I use for imaging.  I am beginning to see that I will have to try a few and see what matches and what doesn't.  If iPolar is the "odd man out," then at least I'll know, but I'll still wonder why.

Edited December 3, 2021 by JonCarleton

[barbulo]

No only the location but the correct actual time is also important for platesolving. Could happen that your OS didn't update the time.

[michael8554]

2 hours ago, JonCarleton said:

PHD2 Guiding Assistant was reporting a very significant polar alignment error (400+/- arc-min)

Were you looking at the Drift in the Statistic boxes under the GA graph ?

That can be badly influenced by any drift outside of the period with guiding off.

The real PAE  is reported in the graph window, right at the end of the GA run.

Post a GuideLog that includes a Cal and GA run..

Michael

[JonCarleton]

I was referring to the PAE in the GA window that updates during the GA run.

I know I should have posted logs.  I'll put some together when there is clear sky again...looks like next week.

[michael8554]

Post the GuideLogs from "a few nights ago" ?

Michael