PHD2 RMS Error on PHD Graph Module


I monitor guiding performance on the PHD Graph module, but I have to switch back to the PHD window to see the RMS error. The graph module takes up a lot of real estate on my smaller laptop screen (I only have room for 2 modules per side), but the graph only uses a small portion of that.

A display of the RA, Dec, and Total RMS error under the graph would be awesome. Also maybe the SNR and/or star mass?

On a similar note, would it be possible or practical to calculate the average RMS error for each exposure duration, and if so write it to the fits header? - Does anyone have any comments on whether this would be useful to aid in image grading?



Looking through the PHD2 API, I don’t see the RMS value passed to clients. Right now this does not look like its possible, but @Andy can “square” (pun intended) me away if I’m wrong.


Right, although the guide offsets for individual guide frames are reported, PHD2 does not know for what range of frames the RMS is “interesting”. In phd2 itself, the RMS number that you see corresponds to the guide frames visible on the graph window. If your graph window shows 100 frames, then the RMS values are for those frames. Often the rms will include dither or other disturbances, so is not quite the actual number you are interested in (rms during exposure).

SGP could calculate the RMS during each exposure from the individual guide frames during the exposure. It’s probably best to do this in SGP since phd2 does not know when the exposure is happening. PHD2 does know about settling complete, so it could report an rms number since that last settle complete? But SGP’s idea of settle complete may not exactly coincide with PHD2 (SGP makes the final call since it decides when to start an exposure.)

If you did want PHD2 to calculate it, we would want to add some messages from SGP to PHD2 indicating “exposure start” and “exposure end”. Then phd2 could also display the in-exposure rms error, as well as reporting it to SGP. Just a thought. Ken, if you want to contact me off-list we can discuss it more.