Re: APPC refraction correction question

Ray Gralak

Am anxious to see what happened.
The problem is with which data points are in a model. Some of the terms have factors that vary directly or indirectly by declination. After subtracting refraction, some values used to calculate pointing terms became non-deterministic, much like right ascension becomes at a celestial pole.

With all the data points being at one declination, the amount of pointing error introduced by not including refraction kept the multi-term best fit "singular" (i.e., one solution) with the pointing terms modeling refraction+other errors.

The solution is simply to use at least two rows of declination data points. Having at least two declination rows would allow APCC to calculate pointing terms that vary directly or indirectly by declination more accurately.

-Ray Gralak
Author of APCC (Astro-Physics Command Center):
Author of PEMPro V3:
Author of Astro-Physics V2 ASCOM Driver:

-----Original Message-----
From: [] On Behalf Of Craig Young
Sent: Friday, July 31, 2020 2:11 AM
Subject: Re: [ap-gto] APPC refraction correction question

Thanks Ray. Here is the pnt file. It consists of 22 samples along a DEC arc of -15 degrees from HA -3 to the
meridian. With refraction correction turned off the Offset error in HA is -170.12. With refraction correction disabled
the model terms are reasonable numbers. With refraction correction enabled you will see the model terms go
really bad. So the model seems good without refraction and samples along a DEC arc, but when refraction is
turned on the model is off the scale. Something dramatic happened. But, if you remove the offset terms then the
model is back to being realistic. Am anxious to see what happened.


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