Why is there no mount with auto-polar-align?

[rogerg]

If a digital compass or an IPhone can find north/south, why can’t an EQ mount with GPS, current date/time, current lat & long, and other computation, be made to have an integrated azmith adjustment to automatically determine north/south and rotate the azmith of the mount to perfect alignment?

Similarly: If a digital angle gauge/angle meter can find 31 degrees elevation, and an iPhone can tell us if our tripod is perfectly flat or not, why can’t an EQ mount be made to have an integrated altitude adjustment and automatically determine the correct altitude (in conjunction with GPS and current date/time data) and move elevate the mount to the correct azmith?

Is this just a case of cost?

I was surprised when the first GPS telescopes came out, as i thought this was what the “you beaut fantastic GPS!” feature would have given us. But now many years later I’m still surprised there’s no mount on the market that will auto-align its self once plonked down on the ground.

Is it just much harder than I’m thinking it is???

Roger.

[mithrandir]

It's another two motors, would rely on the tripod/pier head being perfectly level, known local magnetic variation, and a CCD to confirm the alignment stars were where it though they should be.

Any magnetic compass is only as accurate as the variation you feed it. A bit of reo in the concrete or a nearby steel fence throws my Silva compass off about 5 degrees. Polar alignment needs better values than "S is over thataway".

With a bit of practice it doesn't take that long to polar align, at least for visual.

[rogerg]

I don't see that it should rely on tripod/pier level at all - the fact is you could have a level in the tripod knowing how "off level" it is, this could be taken into consideration quite easily I think.



Interesting. I don't have an iPHone to test it, but I thought if magnetic interference would be a problem then the electronics, battery, metal in a device like an iPhone would have the same effect as reo, if it did affect the type of compass used in such devices?



Of course that's true, but the same could be said for Goto: It doesn't take much to learn star hopping to the point it's extremely efficient to find almost any NGC object, but people still like Goto :)

Thanks for your reply, all interesting food for thought :)

[bartman]

Hi Roger,
There is a scope that auto aligns with a ccd built in.
It's a Meade ETX-LS. According to the article in Sky at Night Magazine - November 2009 - it takes about 10 mins to align and keeps objects in the 'eyepiece' for up to an hour.
I'm not sure if it would be good for astrophotography. I'd buy one if I had some spare cash!
Bartman

[mithrandir]

Mine has a level built in. If I level the tripod both e/w and n/s with a bubble level, including rotating the level 180 deg to even out any error in it, and then look at the built in level, the bubble is outside the centering circle. That can be corrected simply because the error is on the n/s line. I don't know what would need to be done if it was ne/sw.

How accurate do you think the iPhone compass is? I would expect it would do for finding your way around when you are in effect using it as a GPS. My GPSs will all tell me which way is north, but only if they are moving and can work out the course I am on.

The fields induced by the electric currents are small are unlikely to matter. Any magnetic compass is affected by any magnetic materials around it. A fixed compass on a ship can be compensated for the metal in the ship. A portable one can't. You can never tell what will be close enough to affect it.

The iPhone level function has more chance because gravitational variation is much less, assuming a non-accelerated frame of reference.



It is also an alt/az mount, so it is the same set of motors to align and track. The GPS tells the software where the mount is. The CCD lets the software work out where it is pointing.

All in all I don't see it as economic for an equatorial mount.

[renormalised]

Or, you could design a system much like what they have in fighter aircraft, using a gyrocompass and INS. But that would probably become too expensive to do.

[Tandum]

I think maxpoint does something like this. It runs around taking images and plate solves them against a database. Sounds a bit like Barts Meade ETX except you need a camera and PC.

[AndrewJ]

Gday Roger

Automated "polar" aligning is relatively simple, but would be costly for a std EQ mount due to the power required for the extra motors, and possible redesign of the adjustment mechanisms to support automated work.
An IPhone etc will get you close, but for a proper align, ( do reduce DEC drift etc , you need the ability to do very fine adjusments.
Just for fun, i have started to automate my wedge, piccies attached.
I have the DEC working well, but had to redesign the AZ to reduce the power reqd to move a loaded wedge.
The plan is to write a simple application to watch a webby feed whilst drift aligning, and have it adjust the wedge.
One day :D

Andrew

[rogerg]

Looks like a good step forward Andrew! I hope you'll let us know how it all goes when it's finished :)

[g__day]

Roger,

To answer your initial question - its the required precision, versus all the mechanical errors / tolerances of the interacting gear - that makes this economically unachievable.

To get a rough alignment - isn't too challenging. But to get within say 30 arc seconds of your celestial pole, and account for all the flexures and non perfect orthonogality of your OTA components, and account for seeing variations - requires human intervention and a fuzzy logic system.

Simple example - how level can you get your mount. Can you think of a way to get your mount level to within 20 arc seconds. Now also ask is the base of your mount perfectly level in all directions to within a micro metre? I can't think of how one might get the base of a mount level to better than 5 arc minutes of true level.

Next is your OTA perfectly flat on your mount, or is its light path only within 2-3 arc minutes of aligned to the mount holding it?

Do any of the components of your rig flex by more than a few arc minutes or tens of arc seconds - and does this vary with elevation of the target?

Close to isn't too hard to achieve, but the high precision and rigidity of all the interacting components required for long duration, long focal length imaging is very, very exacting.

Look at Tpoint - it may model hundred of stars to account for pointing, tracking, flexure and non-orthonogality of your rigs' components - and it has tens of interacting variables and fitting methods.

Bottom line - the precision required exceeds the economic capability / cost point of the gear amateurs consume.

Matthew

[Steffen]

The iPhone's compass will correct for magnetic declination at your location, but being a magnetometer it is still at the mercy of nearby magnetic materials distorting the field.

Therefore - compass, shmompass! What would be interesting to see is whether the gyroscopic device in the upcoming iPhone 4 will be sensitive enough to detect the Earth's rotation and hence the orientation of the Earth's axis in a reasonably short amount time. That would be the bee's knees for polar alignment. However, I don't think a gyroscope sensitive enough to pull this off with sufficient accuracy would fit inside an iPhone…

Cheers
Steffen.

[Paul Haese]

If PEMPro can get your mount polar aligned to ridiculous accuracy then it must be a simple matter of writing the code to tell several motors to adjust the azimuth and altitude on the mount. It should do this in an iterative fashion. Afterall the accuracy to guide is already present, why wouldn't it be possible to get auto alignment.

Good question Roger. I think this is possible and achievable.

[rogerg]

True, and not only that - systems like the Gemini have built in modelling that can tell you (assuming they work correctly for your hemisphere ;) ) exactly what correction to make to your Alt and Az adjustment in order to achieve perfect alignment. So using something like Gemini you in theory don't need the PC.

This would be a little more time consuming and requiring more user intervention than my initial "plonk it down and it works it out" though :) But close.

Rog.

[Bassnut]

Ive discussed this with Andrew before (yours is taking too long to make Andrew :poke: :P), yes its certainly achievable and infact a fairly simple automation project with an iterative drift algorithm or probably in one hit with Tpoint.

Initially pointing south and leveling only has to be approximate if all 3 axis were contolable.

Its the cost of a 3 axis system thats the problem, not whether its possible or not.

Well, it could actually be "plonk down and it works it out", with only rough level and south pointing.

[bojan]

Why not the processor which controls the movement of AR and DEC axis simply take measurements (via camera) and apply required corrections?
Some dobsonian driver software essentially does this (by performing 3 star alignment procedure) and the whole mount (including ortogonality of the shafts) is analysed and parameters are stored.
Apart from small amount of field rotation, this should be enough.. no need for second set of motors, really.

[Bassnut]

Ive been wondering about that. Tpoint makes a map and compensates for all alignment errors for pointing, but I dont think it compensates RA/DEC tracking, would seem a logical extention and not that hard. Perhaps it does, havent tested drift with an out-of-alignment mount after a Tpoint map.

[rogerg]

Gemini does this when in "Adaptive King" tracking mode, it will use the modelling to track accurately using both RA and Dec. In practice I don't use it because I need to get rid of the field rotation anyhow.

[bojan]

Then there is really no problem for processor to report something like this:
"Move your polar axis by such-and-such to the east, this-and-that up"..
Screws with verniers on them are really not that expensive to make.

[gary]

Hi Fred,

I can answer that for you.

TPoint, on its own, is a pointing analysis system. As you are aware, it provides
the parameters for a pointing model.

In order to get the most benefit from a system such as TPoint, the same pointing
models need to be implemented in the telescope's control system kernel. The
control system kernel is then responsible for pointing and tracking in real time.
Apart from the corrections provided by the pointing model, the control system is
also factoring in effects such as Earth rotation, refraction, etc.

Since tracking is the differential of pointing, good pointing performance is a prerequisite
for good tracking performance if the system is tracking "blind", that is, without the
benefit of guiding on a guide star.

So for telescope's such as the AAT and the Gemini's the operators perform a TPoint
pointing analysis and the parameters extracted from that analysis are then fed into
the scope's control system kernel. Software Bisque with their TheSky and TPoint
offerings also provide a system called ProTrack which they use with their ME mounts
that provides these type of real-time tracking corrections. Our own Argo Navis
has an integrated pointing analysis system called TPAS, the outputted parameters
of which are then used in integrated models in its own pointing and tracking kernel.
So, for example, if you interface a slew and track system to it like a ServoCAT
or SiTech, it feeds them tracking rate data that is being continually corrected
in real time.

To give you an example of the 'static' behavior of a system such as TPoint
and the 'dynamic' real-time behavior of the control system kernel, consider
for one moment refraction. When inputting data into TPoint, the user has
entered their latitude as well as the current atmospheric pressure, temperature
and the computer's system has to have its time accurately set to compute the
current Hour Angle of stars. These parameters are then used to correct the apparent
position of each star owing to the effects of refraction. The control system
kernel, on the other hand, needs to be making corrections owing to refraction
to both the pointing and tracking on a continuous basis. If the temperature or
pressure are different on that night compared to the night of the TPoint run, then
the correction made for refraction at any given elevation will also be different.

As you are aware, polar alignment error in systems such as TPoint and our
own TPAS are treated just like any other source of systematic mount error.
The advantage of this approach, is that unlike a drift test, polar misalignment is
considered simultaneously with all the other errors in the system. Since the
errors are entwined in a complex and knotty way, unraveling the polar misalignment
parameters requires reasonably complex analysis techniques.

Of course, there is also no magic point in the sky to which one can align the
mount's RA axis and achieve a 'perfect polar alignment' that is then valid for all
points in the sky to which the scope can point. In other words, the best place
to align the RA axis of the scope depends on where the scope is tracking at
any one instant. A good compromise is to align the RA axis with the refracted
pole.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au

[Bassnut]

Thanks for that Gary, and the time for such a comprehensive explanation. So thats what ProTrack does ;-).

[AndrewJ]

Gday Fred


The Melbourne weather saps ones desire at times :(
But i do have the DEC done.:D

I can currently watch through my EP and do a smooth "controlled" manual move in Alt or Az of around 10 arcsec, using only 2 fingers.
Using the motor in DEC, its even smoother.
However, i am also using 1/2" UNEF threads on a lever arm of 280mm to do my moves.
When you look at the very short lever arms and coarse threads on most cheaper GEMs, the ability to do low power fine adjusts just isnt there.

Also, why I plan to use the drifting method, vs TPoint etc as
1) Its exceedingly cheap
2) I dont need encoders etc, and dont need to account for any lash in the adjusting mechanism. Just watch the star and move accordingly
3) I was thinking that if you used drifting, at any time during the night,
if you slew to a new locn, you could start a quicky drift test and if necessary, get the mount to micro adjust itself for that locn
This removes all the refraction, flexure etc effects,
and means no complicated models are reqd.
Just point and tweak.

Andrew

[wysiwyg]

Interesting conversation!

I have often wondered how you would go about automating polar alignment. I think without a CCD/Camera feedabck system it would be fairly inaccurate but not impossible.

Having used TPoint with the PME, the process of polar alignment is fairly simple.

1. Level the mount as best you can
2. Point roughly to SCP
3. Home and point telescope to a star as near the home position
4. Take live images and move DEC/RA manually until star in FOV.
5. Center star on CCD chip using Maxim DL
6. Sync
7. Start new TPoint model (6 points minimum)
8. After having slewed to and centered all 6 stars, Tpoint will provide DEC/RA adjustment info fro the PME.
9. Adjust mount accordingly
10. Your done.

Mind you this is the process with a PME as TPoint provides the exact number of tics to move the RA and DEC adjustments.
This will give you a fairly accurate polar alignement but not perfect.

The above process takes about 15 minutes.

It would be fair to say that if TPoint knows exactly what adjustements to take, there would be no problems sending a signal to a couple of servo motors to make the adjustments in tics.

Keep in mind, as soon as you do make adjustemnts you effectively have to re-do the TPoint model. This is a reiterative process to fine tune polar alignment.

To get spot on polar alignment and for pro-track to work effectively you need a 300 point + model to work with, not to mention tweaking the terms and eliminating outliers in your sample size. In my experience this is worth doing when you have a permanent obs, but an overkill for field use. I find a 30 Tpoint point model gets you close enough in the field.

So in motorising the polar alignment and given that the above procedure takes 15 minutes, one would ask if its worth the effort.
The only benefit you would gain in the field is that you would not have to get up from your chair to do it :-)

Mark

[Bassnut]

Mark

The free AAG Tpoint mapper (http://www.aagware.eu/aag_software.htm#MAP) will *automatically* do a 40 point map in 10mins (with Tpoint/pinpoint and Sky on a PME) :thumbsup:. Very tedious manually :P.

[rogerg]

Several people have commented it's quick to do a polar alignment so why bother..

A person proficient with polar alignment can do a good alignment in under 30 minutes. I don’t think there’s any argument that polar alignment can be “quick” and effective using conventional means, but .. that doesn’t stop me looking for a better way :)

If I can plonk down my mount in a field and turn it on, then tell it to polar align, I’d gladly spend my next 30 minutes eating my dinner or chatting to others or planning what to observe, rather than concentrating on timings and fiddling with adjustments :)

It’d also make accurate polar alignment much more accessible to newbies.

It’d also add more “gadget factor” to my setup, which some of us enjoy :)

I don’t see the need for such a feature in permanent setups, it’d almost be a waste of a few good motors and sensors :) Even my LX200 classic on wedge only needs a 10 minute test and tweak every few months.

I’m enjoying reading the discussion of pros and cons, believers and non-believers :)

[wysiwyg]

Yes, thats exactly what I use for larger TPoint models.
You still need that first six or so that are done manually before engaging TPoint mapper though.

[wysiwyg]

I agree whole heartedly, but unfortunately most newbies start off with mounts similar to EQ5's and EQ6's because they are cheap and a great starting point.
However these mounts as you know do not have the mechanical precision required to introduce things like motors to control the ALT and AZ.

Take an EQ6 for example, the ALT adjustment is a two way mechanical process, you undo one bolt to do up another. Unless you heavily modify the base it would be impossible to achieve automated polar alignment, not to mention the cost.

Because all mounts are so different having one system to work for all would also be impossible to implement.

Its not until you get to the PME or AP class mounts where you have the mechanical precision available to you to be able to make such improvements effectively.

Pushing one button to polar align would be nice though :)

Mark

[Bassnut]

mmm, whys that?. I havent needed to.

[Bassnut]

Yes, I can see iteritave drift adjustment working nicely, and cheaper, and easier to manage software wise, but it would take longer, not that that matters much.

Now get it done Andrew, enough Blah :rofl::thumbsup:

[wysiwyg]

Fred, that's a good point actually!

I just read the AAG pdf manual and it says to check the following:
"A TPoint model is available in TheSky6. Note that, if a new model is used in TheSky6, the telescope should be synchronised over a known star"

I guess you can get away without even doing the first six manually and let TPoint mapper do its work. As long as the synced star is in the field of view and roughly centred then pinpoint should do the rest.

Thanks Fred, you just saved me another 5-10 minutes off my polar aligning :-)

[AndrewJ]

Gday Fred



Soooooo correct.
Rock up to Izzos,, plonk down the scope
Start it drift aligning then
down some plonk and wait for the pig to roast:D
( and the IzzoCirrus to form )
Meanwhile, the scope can align itself.
Ahhhhh, Norm would be proud.

Andrew

PS I reckon timewise wouldnt be such a big difference,
as with a webby watching the drift, vs a bloodshot eyeball
it wont take long on each axis
vs waiting till its dark enuf to do a Tpoint run
then adjust
then do a new TPoint run and adjust
then do another ??????
All comes down to how accurately you can adjust the axes
and as noted, yr bog std EQ units have no precision when it comes to this.

[duncan]

Hi All,
Just back from the bush!! Nice to have home comforts again.

However this statement sums itn up!!!!

"Because all mounts are so different having one system to work for all would also be impossible to implement."
Thanks Mark.

Nobody seems to want to work together for the betterment of all anymore.
Imagine how far advanced we could be if everyone worked together for a change?

We would all have huge scopes, just plonk 'em down and within seconds be able to take extraordinary photo's within minutes and then spend the rest of the night with the Missus or Hubby. Damn we wouldn't want that now would we.Haha!!!!!!!
Ah Well ONE DAY!!!!!!!!!!
Come on Andrew! Hurry it up,LOL
Cheers,
Duncan;)

[AndrewJ]

Gday Duncan



Geez, i can start to feel the whipmarks again :lol:

However, my wedge was specifically designed to
allow me to "easily" load a 10" LX200GPS scope
Ie, it folds down flat to allow me to fit the scope in an
Alt/Az position, then the wedge folds back up into position.
Its just a side effect that this design lends itself to
Motorisation of the wedge axes.
As mentioned by others, i also dont see how
a std wedge or EQ type head could be done cost effectively
and i doubt my homemade wedge could ever be made
cost effectively either.

Andrew

[TrevorW]

why is this a good idea

a) not everyone has a permanent site
b) I for one have the SCP blocked by my roofline
c) who wants to stuff around every time they set up aligning and drift aligning etc

[allan gould]

I don't know how many times Ive offered this up, but Alignmaster will get you polar aligned with two iterations that takes about 5 min total. Never use anything else. And you dont need to see the pole.

[TrevorW]

Tried it can't make sense of it Allan never seems to work for me

[Bassnut]

Dont even bother with that, just click and go ;-)

[marki]

Yep it takes a couple of minutes (as long as you can see the required stars) and does a very good job of accurately polar aligning the mount.

Mark

[TrevorW]

School holidays coming up Marki if we get a fine night you can show me how too get this working Cheers

[sejanus]

Allan, does it get you close enough for astrophotography? Or do you still need to drift align to finish it off? I've read differing opinions.

[allan gould]

Several people that I have pointed out this program to, now use it entirely for their polar alignment. In severe cases they have no way of seeing anywhere near the pole and have a limited set of alignment stars. You can edit (carefully) the sterne file and put in your own set of alignment stars. Peter_4059 did just that as he images in a very restricted field of view due to backyard trees etc.
I used three iterations for my observatory based scope and have not had to touch it since. No drift aligning necessary. Prior to my observatory I would set up each night, polar align using Alignmaster (1 or 2 iterations), start PhD guiding and photograph with at least 10min subs. But if you want to check it use a drift alignment or K3CCDTools.

[sejanus]

Well that rocks. Thanks for that. I'll definitely give it a whirl when I get my mount.

[netwolf]

How about no polar alignment by using 3 axis? Alt/Alt/Az

http://www.bbastrodesigns.com/ThreeAxisMounts.html
http://threeaxis.sourceforge.net/

[netwolf]

Sorry to resurect this vert old thread but i saw this on youtube. Please dont focus on the flat earth disproving aspect. But what is interesting is the yse of the drone flight controller to show when a mount is polar aligned the Gyroscope only registers movement in one axis when mount is moved. Just wondering if we could use this in reverse that is polar align until the gyroscope only regsiters movement in one axis?

https://youtu.be/AJOaBGAgyhw

[gregbradley]

I saw a video of a prototype Toast Delight mini tracker mount with a GPS based polar alignment system.

It simply located itself and formed a circle that you adjusted the mount until a cross hair was in the centre of the circle and you were done.

Greg.

[Icearcher]

Thats a awesome idea, you would just need to system to adjust the DEC and RA until it detected no change to two of the axis and Im guessing you could build a self contained wedge that would set up at the touch of a button.

Would work even with no view of the SCP?