I think we have different ideas of how pointing and tracking works. I see them as different things where perfect pointing makes a slew super accurate but after the slew has finished the mount tracks by moving the Ra axis with no further reference to pointing. The Ra and Dec that is generated using the perfect mout model will show the position changing but this does not affect the tracking. I think that will be what the reality is.
dmsummers wrote: Hi Chris,
Thanks for responding and pointing out my neglect of PEC; It was assumed, but I've edited my original post to add this. I'm trying to be precise to understand how this all works (it's confusing enough as it is). I'll disagree (amicably) to a couple of your points.
First about pointing not helping tracking/guiding. The only reason why guiding is necessary is because of inaccurate pointing modeling (beyond PEC). A perfect pointing model would eliminate the need for guiding altogether; any attempt to guide under perfect pointing would result in "chasing the seeing". Thus, any improvement in the pointing model should directly translate to better tracking and smaller guiding residuals until the limit of seeing is reached.
The only position information that the Celestron GPS driver provides is Ra and Dec. I know this because I have been involved in writing the Celestron GPS driver. The Ra and Dec that the HC provides is generated by the mount model in the HC and this will as a minimum use the mount time and position to convert the mount axis values to Dec and Ra.
dmsummers wrote: I also think it's probably not precise to say that Ekos uses mount information through the HC (even though I agree with all your comments on consistency of HC startup procedure). Doesn't Ekos only have a one way command feed to the HC? Wouldn't it be more precise to say that Ekos derives mount position from solved camera images, and then just commands a new mount position via sync command through the HC?