Rotate Without Slew (suggestion)

Use case: You plan to image a target, and want to get everything ready in a scripted fashion including PHD2 calibration and (manual) rotation while the human is awake. And you want to do all this in a reusable template, that will work for different targets which might not be up yet when invoked.

To calibrate PHD2 you need to slew high and near DEC 0. That’s easy and for a given area a specific alt/az works fine, but getting the right rotation for the night is more difficult.

If the target were known to be up, you could slew/rotate to it, achieve the right rotation, then slew to alt/az. But it might not be up yet at the start of the evening (e.g. you will wait in a loop until it is up, but the human does not want to stay up).

A solution I think is a slight variation on the rotate command, a “Rotate without slew” command. It would use the current reported telescope coordinates for a plate solve, but not do a center – just accept the result, but then use the plate solve’s rotation angle so the rotator could do its thing to get the right rotation.

In this way a template could:

Slew to alt/az (same each night)
Rotate without slew (but based on target)
Start guide with calibrate
Stop guide
Human goes to sleep
Wait for target to be above X Altitude
Slew/center/rotate to target (with rotation now already done)

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