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INDI Library v1.9.4 Released (17 Jan 2022)

Bimonthly Stable INDI Library release introduces new drivers and fixes for existing ones. Some highlights:

Meridian flip

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Meridian flip was created by MORELLI

Could someone of the staff, explain clearly the conditions of a meridian flip, with capture & slew and guiding please ?

I observe in simulation that the object position 180° is not on the local meridian, 1° before quasi. If you point an object very near the meridian on the east without crossing it, the mount flips on going to the position. The value for MF is 0 into Ekos.

Thanks so much.
iOptron GM28 - ED80 SW - MAK180 SW - ASI183MM PRO -QHY224C - RPI4 4Go + Stellarmate/Nafabox/Astroberry - Focus motor DIY
2 months 1 week ago #77566

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Replied by MORELLI on topic Meridian flip

I would precise my question:
- Is the MF initiated by Ekos driving the mount or by the mount MF parameters ?
- Is the capture & slew automatic after the MF, the box into the planification tab beeing checked ?
- Idem for guiding ?

We are many people around my country to share these questions. And more I could include your answers into the french PDF documentation I maintain.

Thanks.
iOptron GM28 - ED80 SW - MAK180 SW - ASI183MM PRO -QHY224C - RPI4 4Go + Stellarmate/Nafabox/Astroberry - Focus motor DIY
Last edit: 2 months 5 days ago by MORELLI.
2 months 5 days ago #77779

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Replied by Rishi Garrod on topic Meridian flip

I am also looking forward to the answer to this from someone how knows how this actually works.

My own observations are that if you just have a Sequence running then the mount will flip but imaging will not continue correctly. You really need to do a new plate solve and restart the tracking. If you use the Scheduler then it takes care of plate solving, re-focus if required and tracking.
WO ZS 61
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294 mc pro
224 planetary cam
174 guide cam
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2 months 5 days ago #77781

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Replied by Hy Murveit on topic Meridian flip

@Morelli,

Thanks so much for documenting the system! We really need good doc of Ekos for all languages. 

Wolfgang is the expert on this topic, meridian flips, but I'll take a shot at my understanding of what's going on to get you started. (I'll try my best--but please follow up if I don't respond to what you're looking for.)

Ekos, inside the mount module, regularly monitors the telescope position that your mount hardware broadcasts. If enabled, the mount module will try to initiate a meridian flip once the hour angle condition for a meridian flip is met. This condition is something like "mount on west side of pier, pointing east, and hour angle is positive by a specified amount, e.g. the parameters filled in on the mount tab".  The mount module communicates with the capture module, so if, when the condition is met, and a capture is in-progress, it will wait until the end of that capture.

When the mount module is ready for a meridian flip, and capture is no longer busy, the capture module suspends guiding and tells the mount module to go ahead with the flip.

The slewing part of the meridian flip is really performed by the mount. That is, all Ekos (the mount module) does is issue a slew command to the target position. The target position is usually the current position of the mount give or take a little bit of dithering, guide error, and alignment error. It is basically the desired position from the previous slew. So, all Ekos does is issue a slew command to "the target position (RA/DEC)". It is the mount hardware, not Ekos, which should realize "the target position should really be pointed to from the other side of the pier", and should slew over there.  Most meridian flip issues wind up being caused by this (e.g. the mount not realizing that the pier side should be changed, e.g. because it doesn't think it's near hour-angle=0, or because it has the wrong lat/lon, wrong time, etc). This is why we have meridian flip conditions of a certain margin past the meridian, to insure that a small difference between the mount's position understanding, and ekos' doesn't cause the meridian flip to fail.

When the meridian flip slew is done, and the mount seems to have changed pier sides, the capture module is in charge of resuming processing. It resumes guiding, if guiding was suspended -- i.e. if guiding wasn't running before the flip, it won't start guiding after the flip. It starts up an alignment for the target position. I don't believe there are any parameters that need to be set for it to resume guiding or start alignment. Once those things perform successfully, capture resumes its capture sequence.

Hy
Orion Atlas Pro, William Optics ZS105, Moonlight V2 focuser, GSO RC10 w/RSF focuser
ZWO ASI1600, Astronomik Filters, ST80, QHY 5L-IIm guidecam.
KStars/Ekos/Indi on NUC10 & RPi4 w/SSD -- Ubuntu
Projects: Terrain, Polar Align, Analyze, Linear Focuser, SEP MultiStar & GPG Guide, FITS autostretch.
2 months 4 days ago #77783

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Replied by Paul on topic Meridian flip

Morelli,

You may want to refer to the discussion I have had recently on Meridian flips and the limitations with the current implementation.

indilib.org/forum/mounts/10641-meridian-....html?start=12#77673

Paul
Losmandy G11 with Gemini 2 controller
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Last edit: 2 months 4 days ago by Paul.
2 months 4 days ago #77792

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Replied by MORELLI on topic Meridian flip

@Paul: I read your post before.
iOptron GM28 - ED80 SW - MAK180 SW - ASI183MM PRO -QHY224C - RPI4 4Go + Stellarmate/Nafabox/Astroberry - Focus motor DIY
2 months 4 days ago #77841

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Replied by Scott Denning on topic Meridian flip

For me, the key to successful meridian flips has always been to make the mount settings (either in the driver or the hand control) consistent with the way I'm asking for a flip in Ekos.

For example, set the meridian limit in the mount to something small, like 1 degree past the Meridian. This tells the mount to flip if a GOTO is executed to coordinates more than 1 degree past the meridian

Then in the Ekos scheduler, set the Meridian Flip to take place 3 degrees past the Meridian.

The mount tracks past the meridian, taking exposures. When it reaches 3 degrees west of the Meridian, Ekos issues a GOTO to the RA/DEC to which the mount is already pointing. As Hy says, it's the MOUNT (not Ekos) which then executes the flip.

This example shows why the Ekos flip setting must be FARTHER WEST than the mount Meridian Limit. The important thing is to coordinate the TWO settings: one in the mount itself and the other in the Ekos Scheduler.
Last edit: 2 months 3 days ago by Scott Denning.
2 months 3 days ago #77843

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Replied by Peter Kennett on topic Meridian flip

You state: "...set the meridian limit in the mount to something small, like 1 degree past the Meridian. This tells the mount to flip if a GOTO is executed to coordinates more than 1 degree past the meridian. Then in the Ekos scheduler, set the Meridian Flip to take place 3 degrees past the Meridian."

In my case, with the CEM120 EC2, the exact opposite is needed. If I set my mount to flip 1 degree past Meridian with the mount's hand controller, it will flip 1 degree past meridian, regardless of what EKOS is doing. If I tell EKOS to flip 3 degrees after, it will never get executed, because the mount already flipped at one degree past. This means my exposures are messed up at 1 degree past, since EKOS thinks it can wait until 3 degrees past.

I have to set my mount further west than EKOS, and it becomes a failsafe in the event EKOS doesn't flip for some reason.

iOptron CEM120 EC2 and CEM25P
Celestron C11 EdgeHD
William Optics Star71
ASI 1600Mm Pro, ASI 462MC
Moonlight motorfocus & Esatto focuser
LodeStar X2 and ZWO OAG
DewBuster
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Last edit: 2 months 3 days ago by Peter Kennett.
2 months 3 days ago #77850

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Replied by Paul on topic Meridian flip

Scott,

I think you are overly simplifying thiings.
You need to set the mount up and then configure the software to meet the requirements of the mount.
The problem is that a mount has a range over which a goto will produce a meridian flip but the software is not capable of recognising a range only a fixed limit.
So, you need to set the software to produce a flip after the first point at which it will flip but before it reaches the limit.
Since, Ekos only has one setting it needs to be set to ensure it always commands the goto before it reaches the limit.
For long exposures it may happen that it cannot achieve both and will sometimes fail, depending on when a previous exposure completes.
I have had some discussions with the programmers and they are considering adding an extra setting to fix this but it has not currently been implemented.
So in summary, to ensure 100% flips working you need to have the exposure length shorter than the period between the first point and the limit and to ensure the goto is commanded before the limit is reached.

Paul
 
Losmandy G11 with Gemini 2 controller
QSI 583/683 monochrome camera with filter wheel
Starlight Xpress Lodestar X2 guide camera
Microtouch Focuser controlled using Arduino UNO emulating Feathertouch controller
Raspberry Pi 2GB with Raspberry Pi OS 32bit
2 months 3 days ago #77854

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Replied by Peter Kennett on topic Meridian flip

That is especially important with long exposures - like over 5 minutes long. Your idea is what NINA does. You set the range, and if an exposure would go over the limit, but it is too early to flip, it will pause the exposure sequence until the mount is capable of flipping. This prevents the mount from forcing a flip during an exposure.

iOptron CEM120 EC2 and CEM25P
Celestron C11 EdgeHD
William Optics Star71
ASI 1600Mm Pro, ASI 462MC
Moonlight motorfocus & Esatto focuser
LodeStar X2 and ZWO OAG
DewBuster
NANO PC-T4
2 months 3 days ago #77856

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Replied by Scott Denning on topic Meridian flip

Pretty sure the Ekos Scheduler will NEVER call the goto *during* an exposure.

The logic is as Hy describes. AFTER an exposure, if the hour angle is greater than the specified flip point, Ekos does a goto to the current RA/DEC. It's the mount (not Ekos) that flips.

Peter, from what you describe, your CEM120 does almost the exact opposite of my CEM40! If my mount is within the "tracking past the meridian" limit and Ekos tells it to slew to its current RA/DEC, nothing happens at all.

On the other hand, you describe your mount as performing a flip regardless of what Ekos is doing. In that case the correct thing for you is to just disable the meridian flip in Ekos and let the mont take care of it.

Remember, all Ekos can do is a goto to the current coordinates. It's the MOUNT (not Ekos) that has to know it's time to flip. Many mounts can track well beyond the meridian. If you have your mount set to track say, an hour past the meridian and Ekos tells it to slew to current RA/DEC 5 minutes or 30 minutes past, nothing will happen.
2 months 3 days ago #77857

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Replied by Peter Kennett on topic Meridian flip

OK, now that I am waking up - I realize my comment was not accurate at all. That's what I get for commenting whole half asleep. What I experience is NOT the mount messing up my exposures, but my DOME.
I cant figure out why - but it flips when the mount reaches some point near the Meridian. That's why my exposures get destroyed during the flips. EKOS doesn't know that the dome has moved. I don't even know WHY the dome needed to move. It just goes around and stops at the the position. There are several issues with the INDI Nexdome driver and this is just one of them.

Sorry for the confusing posts.

Peter

iOptron CEM120 EC2 and CEM25P
Celestron C11 EdgeHD
William Optics Star71
ASI 1600Mm Pro, ASI 462MC
Moonlight motorfocus & Esatto focuser
LodeStar X2 and ZWO OAG
DewBuster
NANO PC-T4
2 months 3 days ago #77858

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