Polar Alignment without Polaris (workflow)

Discussions on extending SharpCap using the built in Python scripting functionality
fly_n
Posts: 24
Joined: Wed Oct 02, 2019 7:54 pm

Re: Polar Alignment without Polaris (workflow)

Post by fly_n »

Hello Jean-Francois,
thank you for the log files.
I see the error you are describing. Somehow the Sidereal Time is set to 0.000 for the EQ8 with SynScan and EQMOD, which I don't quite understand.

To make the pointing calculations I need the Sidereal Time, which is a function of the date, time and location.
Unfortunately the Sidereal Time cannot be queried with the SharpCap.Mounts.SelectedMount. function.
I saw three options:
a) have the user enter the ASCOM name of the mount and go through ASCOM to get the number.
I opted against this, as I feared I would not be able to provide a complete list of mount driver names and the selection would take up too much real estate on the GUI.
b) calculate the Sidereal Time with an implementation from a book. I also opted against this idea, as I was not certain it would be equal within a few seconds to the mount and be another error source.
c) lastly I had the idea to use the ASCOM simulator as a source of the information. I thought the ASCOM time would be synchronized with the mount and the location is from the GUI and every ASCOM install also has the simulator... so what could possibly go wrong.
It functions well with the TeenAstro driver, but from your experience does not seem to work with EQMOD / SynScan.

I don't understand why the ASCOM simulator should not work with EQMOD, but if it is so...
Maybe Robin would be so kind to implement a SharpCap.Mounts.SelectedMount.SiderealTime function to make it easier to calculate things or I could try to go with SharpCap.Mounts.SelectedMount.Name and ASCOM to do the query on the actual mount and not go through the simulator.

Kind regards,
Norman
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Re: Polar Alignment without Polaris (workflow)

Post by admin »

Hi Norman,

I will add the sidereal time property to SharpCap 3.3 – watch out for the next update.

Cheers, Robin
fly_n
Posts: 24
Joined: Wed Oct 02, 2019 7:54 pm

Re: Polar Alignment without Polaris (workflow)

Post by fly_n »

Thank you Robin, that will be helpful.
I just noted that the SharpCap.Mount.SelectedMount.Name route would not work, as ASCOM would like the ProgID and not the name.

Jean-Francois, I was playing with the refraction on actual images and trying to see if I could use an optimizer to find a temperature and pressure combination, that would give the 'perfect' refraction answer for that image series.

What I noted however was the following, the optimizer was chasing it's own tail.
The reason for that is twofold.
A) above about 15° ALT, the refraction is close enough to a linear function, considering other uncertainties.
B) in order for the math to work, I need to set the DEC values such that they are set onto a plane that is rotated about the ALT axis.
I use a constant offset for that. If I subtract any refraction that is quasi linear, it looks just like a small additional rotation.
But as the real answer is unknown, the optimizer cannot figure out what part of the steepness or offset of the refraction is real and what is not.

I guess a derivative of this script could determine the actual refraction by slewing in DEC direction, but I would not expect it to be helpful in the end.
Curious and funny, but likely not helpful in getting better pictures.

Kind regards, Norman
fly_n
Posts: 24
Joined: Wed Oct 02, 2019 7:54 pm

Re: Polar Alignment without Polaris (workflow)

Post by fly_n »

Hello Jean-Francois, Robin,

thank you for the implementation of the SiderealTime property in the latest 3.3 Beta.
I've modified the script to use this now instead of going through the ASCOM telescope simulator.
It's working on my end so please give it a try if you like.

Kind regards,
Norman
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