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kens

New PHD2 tool for static polar alignment

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kens    135

It's been 18 months since I first started working on a tool for polar alignment in the polar region using a guidescope.

Now it's a tool within PHD2 and available in the latest dev release. Documentation will follow shortly.
Why static alignment? No reason other than to distinguish from the various forms of drift alignment.
This tool lets you polar align by pointing at the pole rather than the equator and in my testing so far is pretty quick. It works particularly well in the Southern Hemisphere due the availability of several identifiable stars near the pole. 
Feedback welcome.

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johnrt    2,178

How close to the pole do you have to point for it to work? I have Polaris blocked for most of the year by trees. 

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kens    135

It is designed to work close to the pole as opposed to drift alignment. There is a choice of 6 alignment star of which one is Polaris. The others are fainter and all are closer to the pole than Polaris. In theory it can work up to 5 degrees from the pole but we would have to add more alignment stars. Only one of the alignment stars is needed.

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GuLinux    146

Interesting, I'll give it a go.

Is this somewhat similar to Firecapture and Ekos polar alignment modules?

I was about to start coding something similar as well, since Firecapture is Windows only, while Ekos tool has a quite "restrictive" workflow, designed for automated observatories, and quite  difficult to adapt to a StarAdventurer, and I wanted something much closer to Polemaster.

I certainly hope yours will suite me :D

Just a question: any particular reason you shipped it with PHD2? 

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kens    135

Should be as safe to download as any other version of PHD2. I chose PHD2 in order to take advantage of the guiding capability which enabes the star locations to be accurately recorded and thereby reduce the amount of slewing needed. Fitting the main algorithm into PHD2 was relatively easy with few changes needed to the core code. Plus it works on both ASCOM and INDI and on all the main platforms: Windows, Linux incl ARM and OSX.

The algorithm is similat to that used by Polemaster. Ekos and Sharpcap use platesolving and I though this was a nice complement to PHD2s drift alignment as it gives the user a choice of aligning at either the equator or at the pole depending on their situation. Attached is a screen shot of what to expect:

The window shows the positions of the alignment stars as they should appear in your FOV. The mount rotates on command to select two points and calculates the centre of the arc. The two points are shown on the main display as small blue circles. You can see how small a slew distance is needed to calculate the magenta circle. The red and blue lines show the alt and azimuth adjustments needed to bring the centre of rotation to the pole. The main adjustment needed here was in azimuth (blue).

 

TEST03.png

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GuLinux    146

Cool.. pretty much what I was looking for :) I might try to contribute, although I have no previous experience with wxWidgets.

Does it also work with a large FOV, like the Polemaster itself? I have an ASI 178mm with a 25mm c-mount lens, I was planning to use that as a polar assistant tool.

1 minute ago, kens said:

The mount rotates on command to select two points and calculates the centre of the arc.

This might be a problem: as I stated before, it should also work for manual mounts (like the Star Adventurer, the RA motor is way too slow to rotate a decent amount of degrees).

Do you support, or plan to support, manual mount rotations?

 

Cheers,

Marco

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kens    135

A larger FOV should generally make it easier to find an alignment star. There is already a manual option. It can either be selected by ticking the Manual Slew box or for manual mounts that is the default. With a manual mount (or On Camera)  you need to manually select three points. The images assume that your mount is in the "home" position i.e. pointing at 18 hours HA.

The screen shot shows what manual mode looks like. Seeing as the display does not neceesarily show the correct star positions I recommend to instead adjust the alignment stars onto their respective circles (the concentric yellow and green circles). With three stars on the correct circle the mount is aligned

DOC13.png

Edited by kens

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spillage    288

There appears to be a check box for manual slew and I think if you just connect to a guide cam but not a mount then it will open in manual mode. I am at work so only had a look using simulators but it look very promising and I am looking forward to testing this out.

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kens    135
4 minutes ago, spillage said:

There appears to be a check box for manual slew and I think if you just connect to a guide cam but not a mount then it will open in manual mode. I am at work so only had a look using simulators but it look very promising and I am looking forward to testing this out.

That is indeed the case. In fact if you connect to any mount that cannot slew under computer control e.g. On Camera it wil default to manual. In manual mode you need to select your hemisphere so the right stars are shown. I wasn't able to test that fully so I was relying on comparing to Stellarium to get the right orientation.

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michael8554    409

G'day Ken

Def will give it a go next clear night.

Does the guidecam have to be concentric with the imaging camera?

How does the Align at the Equator work please?

Michael

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spillage    288

@kens

Will this work like sharpcap in the way that I can fire up the mount and slew to get polaris in view (if its not) and then run the 1st, 2nd and 3rd position steps.

@michael8554

I dont think it matters about the guide cam being concentric (like sharpcap) and you would align it from the home position when pointing to polaris (if in the north).

Typical that the clouds rolled in tonight just as it got dark. Will be interested to see how my guidecam and scope do and if there are any differences between this and drift alignment as sharpcap and phd drift always seemed a bit out of syn with each other.

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kens    135
3 minutes ago, spillage said:

@kens

Will this work like sharpcap in the way that I can fire up the mount and slew to get polaris in view (if its not) and then run the 1st, 2nd and 3rd position steps.

@michael8554

I dont think it matters about the guide cam being concentric (like sharpcap) and you would align it from the home position when pointing to polaris (if in the north).

Typical that the clouds rolled in tonight just as it got dark. Will be interested to see how my guidecam and scope do and if there are any differences between this and drift alignment as sharpcap and phd drift always seemed a bit out of syn with each other.

Yes - its similar to SharpCap. But in auto mode the mount slews automatically and only needs to collect two positions.

@michael8854 The reason for collecting the star positions is to calculate the alignment of your camera/scope with the mounts RA axis. You can use either your imaging scope/cam or guide scope cam as long as PHD2 can connect to it.

 

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kens    135
3 hours ago, michael8554 said:

G'day Ken

Def will give it a go next clear night.

Does the guidecam have to be concentric with the imaging camera?

How does the Align at the Equator work please?

Michael

Aligning at the equator is the normal PHD2 Drift Alignment. You first track the drift of a star near the meridian and Dec 0 (equator) to determine the azimuth adjustment. Then do the same for a star near the horizon and dec 0 to determine the altitude adjustment.

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michael8554    409
16 hours ago, kens said:

Aligning at the equator is the normal PHD2 Drift Alignment. You first track the drift of a star near the meridian and Dec 0 (equator) to determine the azimuth adjustment. Then do the same for a star near the horizon and dec 0 to determine the altitude adjustment.

Thanks Ken

So you mean the original PHD2 polar alignment - I was hoping for a version of your new alignment, as yours gives a much more intuitive display of which way to move the mount !?!  

Michael

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kens    135
2 hours ago, michael8554 said:

Thanks Ken

So you mean the original PHD2 polar alignment - I was hoping for a version of your new alignment, as yours gives a much more intuitive display of which way to move the mount !?!  

Michael

My version does the alignment in the polar region rather than at the equator. First download and install the dev snapshot from https://openphdguiding.org/development-snapshots/

Run PHD2, connect camera and mount, make sure you have calibrated and are pointing near the pole

Under the Tools menu select "Statis Polar Align". A window pops up with some instructions.

Use the graphic to select a reference star on the main displa and identify it withthe drop-down list.

Click Rotate and let the tool do its thing.

Adjust in altitude to move the reference star along the red line, and in altitude to move along the blue line. (the on screen instructions say orange and green - I'm changing that)

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spillage    288

sorry is the red alt or az. Also (too cloudy to have a real go tonight) as you move the alt az will the red/blue line decrease in real time or do you need to click the calculate button each time an adjustment is made.

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kens    135

Alt is red. The overlay is static but the centre of rotation does not move as you adjust. What you are doing is moving the celestial pole to coincide with the centre of rotation. One you've made your adjustments you could slew in dec to recentre then rerun the process from the start to check your alignment if you want. I'm most interested to hear about the choices for reference stars and how easy or otherwise to find them

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spillage    288

Last  night was probably not the best night to be trying this out with patchy cloud and I sure I had  a few gremlins lurking in the background. I appreciate that I do have an old qhy5 mono so will not be as sensitive as a newer cam.

I did find the reference stars a little hard to choose from as they did not appear in the same position as my live view. It felt like you needed to guess which was which.

Not sure if this may be due to my image size.

It did however only take few minutes to calculate and it appeared that if cloud passed by then it was happy to sit there and continue calibration once it was clear enough.

It is looking very impressive and I hope this is of some help.

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