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INDI Library v1.9.6 Released (21 May 2022)

Bi-monthly INDI Library released with new drivers and bug fixes.

Polar Alignment Adjustments

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When ekos does a Alt/Az error calculation and reports too high/low/east/west, is this referring to the current polar axis relative to true north?

I had a quick test run with it the other night before the fog rolled in and whilst the Alt adjustment worked fine, moving the star back to the center reduced the error nicely. I had issues with the Az adjustment.

I had "Northern Hemisphere" and "West" selected and used a star in the south and a star in the west for Az and Alt alignment respecitvely. When calculating the Az error using the southern star, Ekos reported that it was "too far east" yet when I adjusted the wedge to move it westward and recalculated, the Az error increased ( I ran the calculation a couple of times to be sure). If I instead adjusted the wedge to the east* the Az error would decrease.

That intself isn't realy an issue, however, when I then centered on a southern star in kstars and went to perform the Az Correction, the telescope slewed towards the west (to the right of the southern star in kstars) by the amount the Az error showed. However in order to re-center the star I had to move the wedge west which caused the Az error to increase.

Have I setup something incorrectly in ekos that would cause this issue with Az adjustments to provide a wedge adjustment in the wrong direction and/or slew in a way that recentering increases the error? Would the orientation of my CCD impact calculations?

I'm assuming this is user error as it's the first time I've tried the polar align solvers. On the off change there was a bug similar to this, I'm running the Debian Jessie version of kstars 4.14.2 and whichever version of ekos is bundled with it.

Any suggestions to try the next time there's a clear night to retest?

* When I say "adjust the wedge to the east" I mean standing behind the scope, looking north, I'll tighten the left hand knob and cause the wedge to rotate towards the east.
Last edit: 7 years 1 month ago by Gary.
7 years 1 month ago #3857

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Hi Gary, yes there was a bug regarding east/west and it was fixed in kstars-bleeding.
Jasem Mutlaq
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7 years 1 month ago #3861

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Replied by Gary on topic Polar Alignment Adjustments

I'll build a newer copy then, cheers :)
7 years 1 month ago #3864

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Replied by Gary on topic Polar Alignment Adjustments

Do you happen to know which commit fixed this? I've had a trawl through the logs but can't find anything to do with Az correction/east/west keywords that looks related.

I had a look at building master (assuming that's what you meant by kstars-bleeding?) and it looks like Debian Jessie may be missing a few dependancies e.g no kde5, cmake_extra_modules (for emc_install_icons, although that can be pulled from experimental), missing qt5qml cmake file...

It may be simpler if I just patch just this one bug fix into the current Debian package, or the latest kde4 version of kstars that builds on Jessie.
7 years 1 month ago #3869

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Not sure, will have to look at the logs. And yes it is quite hard to get latest KStars unless you're on Ubuntu/Fedora/Gentoo for now. Debian is probably not best suitable for bleeding edge stuff.
Jasem Mutlaq
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7 years 1 month ago #3872

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Replied by Gary on topic Polar Alignment Adjustments

I've compared the 4.14.2 version with kstars master and for the ekos/align.cpp there's a swapping of the East/West text
if (decDeviation > 0)
   deviationDirection = kxi18n("%1 too far east");
else
   deviationDirection = kxi18n("%1 too far west");

Which will resolve manual corrections where too far east is reported and having to then move wedge east to correct when you'd expect to move it west based on the report. I'll make that change in my version too :)

I can't see anything that would impact the Az Correction slew direction though. Have you recently tried centering the target star for Az correction and whether doing so reduced or increased the Az error? For me, it increases it and the only change I can see related to this is the above labelling swap.

In calculatePolarError (line 1058 in older version) there's
 if (azStage == AZ_FINISHED)
    {
        azError->setText(deviationDirection.subs(QString("%1").arg(fabs(deviation), 0, 'g', 3)).toString());
        azDeviation = deviation * (decDeviation > 0 ? 1 : -1);
        correctAzB->setEnabled(true);
    }

Which is the same in both versions. If the East/West labels were inversed, is it possible the 1/-1 values are also inversed? As I'm seeing the scope slew west in kstars which means the wedge must be moved westward in order to recenter the star yet doing this increases the Az Error.

For example, with the above east/west label change, the scope would now report "too far West" and require me to move the wedge eastward to reduce Az Error. In terms of recentering a star this should then (I think?) imply that the scope should be slewed east of the southern star so that moving the wedge east would bring the star back to the center.

I can't see where that has being fixed in the latest version though?
Last edit: 7 years 1 month ago by Gary.
7 years 1 month ago #3932

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It used to be "move your mount east/west until the star is centered" and now it's just "move your mount until the star is centered". I haven't had a clear night in quite a while, so I'll give it a go when I can and let you know the results.
Jasem Mutlaq
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7 years 1 month ago #3936

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Sorry for may be stupid question, but where it is possible to find explanation how to accomplish polar alignment using Ekos? I was trying Celestron own algorithm and the classical drift method using eyepiece with reticle but still struggle with achieving good results. I would like to give a try with Ekos!
Linux Mint 17.1 + Kubuntu 14.10 hybrid OS, using PPA for latest KStars-bleeding and INDI
7 years 1 month ago #3944

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Replied by Gary on topic Polar Alignment Adjustments

Have a look at the alignment module page .

There's a few videos on youtube that cover the goto module, not sure if there's one for doing polar alignement though.

I've used the drift method up to now, it can get you very accurate results, but it can take a lot of time to close in. Ekos lets you point at a star in the south (for az) and a star in the east or west (for alt), takes two images and tells you how far out your wedge is. Then you can just adjust the wedge and let it measure again. Or, you can use the Az/Alt correction button and it'll slew the telescope then ask you to recenter the star.

It's probably worth getting the GOTO solving module working first as the polar alignement option depends on the same solver.
The following user(s) said Thank You: Alexandru Barbovschi
7 years 1 month ago #3946

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As I expected my question was stupid - I could find myself corresponding page :) There is no video btw.

A new question arise - is alignment (GOTO) of the Celestron NexStar improved with more sync points as it does for EQMod?

P.S. Is Polar Alignment usable now?
Linux Mint 17.1 + Kubuntu 14.10 hybrid OS, using PPA for latest KStars-bleeding and INDI
Last edit: 7 years 1 month ago by Alexandru Barbovschi.
7 years 1 month ago #3955

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While waiting for the answer I got one more question. I tried last night polar alignment. Really easy and good, but not fully clear for me. Here:

What point? After the slew to this point Ekos asks me to center the target. What target? I don't see it mentioned anywhere... Which star to bring to the center? Am I missing something?
Linux Mint 17.1 + Kubuntu 14.10 hybrid OS, using PPA for latest KStars-bleeding and INDI
7 years 1 month ago #3981

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Ok, I updated the instructions, is it any better now?
Jasem Mutlaq
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7 years 1 month ago #3983

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