PHD2 and 'step' guiding

[Reid Smythe]

I'm developing a 3rd party ASCOM driver for a mount.  This mount doesn't quite behave in accordance with the ASCOM standards when pulse guiding: it will take the duration and speed to develop a distance and 'step' the mount rather than move at the guidespeed for duration.  

For example: if it receives a guideNorth command for 5000 ms at a guide speed of 0.2"/sec, it will step the mount 1" in the guideNorth direction.  This is contrary to the ASCOM PulseGuide method which expects the mount to move for 5000 ms at 0.2"/sec.

Picking through a bit of the PHD2 source, it looks like the only implication is that you will not see the IsPulseGuiding property be true (it basically flips on and off in a matter of a few ms) and it looks like you internally keep track of the pulse length and won't send another command on that axis until you would expect the last pulse to be finished.

From the PHD2 perspective, in terms of minimizing the potential for failures or errors, would it be better to artificially maintain IsPulseGuiding true for the duration of the ordered pulse or report the true status of the hardware although the mount behavior will be unexpected?

[bw_m...@earthlink.net]

I think the safest approach would be to implement the pulse-guide method as a synchronous call and have the driver impose a delay for the requested pulse-guide duration.  That will conform with the ASCOM standard and your driver will behave many others, so there won’t be any unpleasant surprises.  When you return from the function call, just be sure that IsSlewing and IsGuiding are false.  Of course, you could accomplish the same thing with an asynchronous function but that might complicate the logic in the driver.

 

Regards,

Bruce

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[Reid Smythe]

I actually had the synchronous solution implemented recently, however ASCOM 7 is making PulseGuide explicitly async so I put in the logic you mentioned above for that solution.

I will leave that as the default behavior of the driver, thanks!

R/

Reid

[bw_m...@earthlink.net]

Sounds good, let me know if you need any help.  We have a MountExerciser tool that can mimic what PHD2 does during calibration which is useful for daytime testing.

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