I've also given this some though but have yet to do more than that.
As I understand it the process would go something like this:
- Get GPS co-ords, date and time and send to handset.
- Select alignment method (this may need to be done manually on the handset)
- Select first aligment star/object
- Take wide field photo through scope and analyse (google plate solving) to work out where scope is currently pointing.
- Find co-ords of alignment star
- Convert that into a more command for the scope and send it.
- Take wide field photo through scope and analyse to work out where scope is currently pointing.
- Repeat above steps 5-7 if scope is not pointing at alignment star.
- Tell handset scope is aligned on target
- Select second alignment star and repeat steps 4-9
Now the gotchas:
- Co-ords used by the motor controller do not have a fixed zero point. It's reset to where ever the mount is pointing at power on.
The plate solving software I've looked at return co-ords in RA/Dec format. These would have to be converted into a form suitable for your Alt/Az mount, and possibly for the format needed by the motor controller board.
The pi may not be powerfull enough to perform the plate solving in a reasonable time.
A Couple of possible work arounds:
- Putting the scope to a know position and zeroing the encoders before staring alignment may simplify some of the calculations. Meade were doing this in some of their scopes with their "level north" system.
I think there's a thread on the forum somewhere about using an online service for plate solving.
If the nextstar protocol allows it, it may be possible to skip most of the process by calculating the initial poisiton, feeding that to the scope and telling it that it has been aligned. I don't have the docs to hand to check this though.
On the hardware front, on my skywatcher mounts (which also use the nextstar protocol), communication between mount, handset and attched computer is by serial. 5v ttl between mount and hanset but full RS232 levels between handset and computer. Neither of these can be connected directly to a pi.
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