Strange numbers in APPM model #APCC #Mach2GTO


David Johnson
 
Edited

I've been using the Dec Arc feature, and it seems to work well.  Thank you for implementing it.  However, some of the numbers I'm getting for the model parameters are many orders of magnitude different than the usual values.  For example, I'm doing a model with two arcs, one at 61 degrees N declination and one at 63 degrees.  Below you can see what it looks like.  The resulting model numbers are also shown below.  Notice some of the "west" parameters.

The mount tracks well, so it's not a functional issue, but it puzzles me that the numbers are so different.  Is this caused by doing the two arcs close together and no points elsewehere?  If so, would I have major issues if I tried to do regular tracking correction away from the two arcs?  I doubt I would do that, because I'm obviously concentrating on a target between the two arc declinations, but I do sometimes change targets for unforeseen reasons, and maybe if I do I should just turn tracking off if I don't want to do another model?




Ray Gralak
 

Hi David,

some of the numbers I'm getting for the model parameters are many orders of magnitude different
than the usual values.
The all-sky model requires data in a larger area of the sky to accurately determine the pointing terms, so you cannot count on the all-sky pointing terms being accurate with just a few rows of declination arcs.

If you are in a permanent setup, the ideal way to get the advantages of declination arc tracking accuracy and all-sky modeling is to capture a lot of data points (400+) so that there are many declination arcs throughout the entire sky.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of David Johnson
Sent: Thursday, September 2, 2021 6:10 PM
To: main@ap-gto.groups.io
Subject: [ap-gto] Strange numbers in APPM model #APCC #Mach2GTO

[Edited Message Follows]

I've been using the Dec Arc feature, and it seems to work well. Thank you for implementing it. However,
some of the numbers I'm getting for the model parameters are many orders of magnitude different than the
usual values. For example, I'm doing a model with two arcs, one at 61 degrees N declination and one at 63
degrees. Below you can see what it looks like. The resulting model numbers are also shown below. Notice
some of the "west" parameters.

The mount tracks well, so it's not a functional issue, but it puzzles me that the numbers are so different. Is
this caused by doing the two arcs close together and no points elsewehere? If so, would I have major issues
if I tried to do regular tracking correction away from the two arcs? I doubt I would do that, because I'm
obviously concentrating on a target between the two arc declinations, but I do sometimes change targets for
unforeseen reasons, and maybe if I do I should just turn tracking off if I don't want to do another model?





David Johnson
 

Understood.  Mount tracked extremely well last night again.  Results here. The mount tracks so well unguided that I think I’ve forgotten how to guide.

I definitely like the idea expressed in another thread of some simple tools in APPM to help set up for Dec Arc tracking. Right now, it’s definitely doable but a little clunky. For example, being able to just input the declination of your target and maybe some altitude limits and have it automatically generate good points for Dec Arc tracking would be very nice for those of us that setup and breakdown often.  As it is, it’s not hard once you get the hang of it. 


Chris White
 

 If so, would I have major issues if I tried to do regular tracking correction away from the two arcs? 

I dont think so. I believe that if you move to a location beyond your dec arcs that it reverts to all sky for correction, and I assume that if an all sky model is not present that it would just revert to standard sidereal tracking...


Dean Jacobsen
 

On Fri, Sep 3, 2021 at 07:12 AM, David Johnson wrote:
Mount tracked extremely well last night again.  Results here. The mount tracks so well unguided that I think I’ve forgotten how to guide.
Nice shot David. 

I have been doing unguided imaging with the Mach2 for more than a year now and I couldn't be happier with the mount and the software tools.  The guide scope and guide camera have been sitting on the shelf collecting dust.

I also imaged the Sharpless 2-155 area.  My view is a little wider than yours though  --> https://www.astrobin.com/udzsan/E/
 
--
Dean Jacobsen
Astrobin Image Gallery - https://www.astrobin.com/users/deanjacobsen/