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.
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.
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).
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.
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.
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.
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.
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.
If you go to the GPG Options page (described above) and enter the mount period in "Major Period", and click apply, then KStars should remember it.
If "Estimate Period" is not checked, then the period should not be updated by GPG.
As I said, either look up the period if it's on the PHD2 Wiki page above, or keep a good estimate from a successful KStars GPG session that lasted
a long time, e.g. over an hour since the last slew or other GPG reset.