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INDI Library v1.9.7 Released (29 Jul 2022)

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

How does PEC/PPEC & GPG work to help RA guiding

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Hi,

I have terrible PE in my RA axis and I have seen the PPEC tab in the mount module & GPG in the guide module in Ekos but could never figure out to use it. So I have a couple of questions:
1. Can I use these to correct for the PE in my RA axis?
2. How do I use them? I’ve searched and can’t find any step by step instructions.

Cheers

Rene
Sky-Watcher AZ-EQ6
Sky-Watcher Esprit 100
Sky-Watcher EvoGuide 50 (guide-scope)
ZWO ASI294MC Pro
ZWO ASI120MM mini (guide cam)
Pegasus PPB
Pegasus Focus Cube v2
Last edit: 1 year 6 months ago by Rene.
1 year 6 months ago #66082

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Rene,

GPG should improve your PE for sure. It takes a few mount periods to reach its full potential (as it has to sample your periodic error before it can correct it).
More or less, all you need to do is check the box to turn it on (and it's probably best to also set the period--see below).

- In the guider tab, click Options in the lower right corner.
- Click on "GPG RA Guider" on the left to get to the GPG section
- Check the enable GPG checkbox.

The only control you should consider changing is to set "Major Period" with the period of your mount and, if you know that, disable the "estimate period" checkbox.
You would only do that if you knew your mount's period. Many are given on this PHD2 wiki page: github.com/OpenPHDGuiding/phd2/wiki/Mount-Worm-Period-Info
If you don't know it, you can let the GPG system estimate it, and then if you were happy with the guiding, e.g. after an hour, re-open that menu, look at the value it's estimated,
and freeze that value in there by unchecking estimate period. Of course, I suppose you could let it continue to always estimate, but it will get to its best sooner
if you give it the right period to start with.

Once it's setup, then you're good, and run guiding as you would.
The RA guiding is then controlled by this GPG algorithm.

Let me know if you have any further questions, and/or let us know how it goes.
Hy
AP1100 & Orion Atlas Pro, WO/ZS105 w/Moonlight V2 focus, GSO RC10 w/RSF focus
ZWO ASI1600, Astronomik Filters, ST80, QHY 5L-IIm.
KStars/Ekos/Indi on NUC10 & RPi4 w/SSD -- Ubuntu
Projects: Greedy Scheduler, Terrain, Polar Align, Analyze, Linear Focuser, SEP MultiStar & GPG Guide, FITS autostretch.
The following user(s) said Thank You: Andres Rossi
1 year 6 months ago #66086

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Thanks Hy. That clears things up.

Do I run GPG in concert with PPEC/PEC? If so what steps do I take to run PEC/PPEC (fyi I have a SW AZEQ6 GT)

Cheers

Rene
Sky-Watcher AZ-EQ6
Sky-Watcher Esprit 100
Sky-Watcher EvoGuide 50 (guide-scope)
ZWO ASI294MC Pro
ZWO ASI120MM mini (guide cam)
Pegasus PPB
Pegasus Focus Cube v2
1 year 6 months ago #66088

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Sorry, I haven't done any periodic error correction on my Orion Atlas Pro and am not really on top of that. Perhaps others can help out.
If you do correct your mount that way, which sounds like a good idea, then GPG's improvement will be less, of course,
though I don' t expect it to hurt to use both. Let me know if you do wind up doing that.
AP1100 & Orion Atlas Pro, WO/ZS105 w/Moonlight V2 focus, GSO RC10 w/RSF focus
ZWO ASI1600, Astronomik Filters, ST80, QHY 5L-IIm.
KStars/Ekos/Indi on NUC10 & RPi4 w/SSD -- Ubuntu
Projects: Greedy Scheduler, Terrain, Polar Align, Analyze, Linear Focuser, SEP MultiStar & GPG Guide, FITS autostretch.
1 year 6 months ago #66089

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FWIW, here's my imaging session from tonight, so far, using GPG for the RA guiding.
You can see the Atlas Pro's periodic error pretty clearly at the start, but it seems to be reduced after about 21:05.
It's not an ideal night (you can see the SNR dip around 21:20).

AP1100 & Orion Atlas Pro, WO/ZS105 w/Moonlight V2 focus, GSO RC10 w/RSF focus
ZWO ASI1600, Astronomik Filters, ST80, QHY 5L-IIm.
KStars/Ekos/Indi on NUC10 & RPi4 w/SSD -- Ubuntu
Projects: Greedy Scheduler, Terrain, Polar Align, Analyze, Linear Focuser, SEP MultiStar & GPG Guide, FITS autostretch.
Last edit: 1 year 6 months ago by Hy Murveit.
1 year 6 months ago #66090
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Hi Rene, I have spend some time with research about PPEC. The fact is, that it is not usable in Ekos if you also want to use guiding. Those two functions ara fighting against each other. But if I summarize it, how to use PPEC:
1) You will need to record correction curve. For this, you will need to switch from INDI to ASCOM, because INDI driver for EQDir is simple, and it doesn't have this capability.
2) Once your curve is recorded, you can smooth it in PECPrep. This step is optional, but I would recommend to do it.
3) You will need to replay the (smoothed) curve from EQDir under ASCOM. At the same time, you will need to learn the mount the curve. This can be done in Ekos, with one of those two buttons in PPEC tab.
4) Finally, you can enable PPEC during your imaging session. RA periodic error will be automatically corrected by the mount itself, as the correction curve is now recorded in its EEPROM.
As I said, it is way too complicated, and GPG for this purpose is definitely better solution, as it is able to cooperate with guiding.
1 year 6 months ago #66091

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Thanks for that. So are you saying I should use GPG in Ekos instead of PEC/Prep/PemPro? So what is the periodic error tab in the indi control panel used for. if anything?
Sky-Watcher AZ-EQ6
Sky-Watcher Esprit 100
Sky-Watcher EvoGuide 50 (guide-scope)
ZWO ASI294MC Pro
ZWO ASI120MM mini (guide cam)
Pegasus PPB
Pegasus Focus Cube v2
1 year 6 months ago #66212

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The tab could be used for two things:
1) Start programming PPEC into the mount
2) Enable PPEC once it is programmed in the mount
Once you click on one of these two options in that tab, it will simply turn ON (or OFF) a flag in the mount's electronic. Nothing more, nothing less.
Last edit: 1 year 6 months ago by hades.
1 year 6 months ago #66219

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So if I use GPG during my guiding, does it retain the adjustments from session to session or does it have to recalculate? I’m hoping it retains the information so I don’t have to waste time each imaging session.

Rene
Sky-Watcher AZ-EQ6
Sky-Watcher Esprit 100
Sky-Watcher EvoGuide 50 (guide-scope)
ZWO ASI294MC Pro
ZWO ASI120MM mini (guide cam)
Pegasus PPB
Pegasus Focus Cube v2
1 year 6 months ago #66293

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Unfortunately it doesn't store that information, and needs to start from scratch each time. That's why I recommend at least saving the mount period.

When I introduced this to KStars, I asked GPG's developer, Edgar Klenske, who's developed this as part of his PhD, the same question. He said that was possible but never done, and not a trivial task.
I think this is unlikely to happen in the near term.
AP1100 & Orion Atlas Pro, WO/ZS105 w/Moonlight V2 focus, GSO RC10 w/RSF focus
ZWO ASI1600, Astronomik Filters, ST80, QHY 5L-IIm.
KStars/Ekos/Indi on NUC10 & RPi4 w/SSD -- Ubuntu
Projects: Greedy Scheduler, Terrain, Polar Align, Analyze, Linear Focuser, SEP MultiStar & GPG Guide, FITS autostretch.
1 year 6 months ago #66295

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Thanks Hy,

Silly question but how do I save the mount period? :)

Rene
Sky-Watcher AZ-EQ6
Sky-Watcher Esprit 100
Sky-Watcher EvoGuide 50 (guide-scope)
ZWO ASI294MC Pro
ZWO ASI120MM mini (guide cam)
Pegasus PPB
Pegasus Focus Cube v2
1 year 6 months ago #66296

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I think that GPG could be saved for next session. But you need to have a mount with encoders or at least with an index on the RA axis, e.g.: SW EQ6-R. Because the algorithm needs to know at which RA possition is the mount. This is how it works for PPEC.
1 year 6 months ago #66302

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