APPM - offset when telescope is powered off and then powered on a day or later #APCC


Dan R Price
 

I am having a minor problem with APCC/APPM.  I begin with running APPM for about 30 points, all near the DEC of my target for the evening.  This works just fine.  Once APPM is done I run TheSkyX, find my target, switch over to SGP and run the imaging sequence for several hours.  This works just fine.  I then park the Mach2GTO and power off everything (telescope, computer).  I am very careful not to touch the telescope or mount.  The next evening I power everything up and assume I am good to go.  I run TheSkyX, find my target and slew to it.  I then take a simple image to check location and always find I have an offset of roughly 10 arc minutes from my location the night before.  I then go to APPM and do a Verify for a couple of points.  The Verify says I am .1 arc minutes or better.  At this point I abort the Verify.  I then go back to TheSkyX, do a find on my target and slew to it again.  This time the target position is almost perfect.  The rest of the evening goes smoothly.  My question is - what am I misunderstanding about APPM (or TheSkyX) that requires I run APPM/Verify on a couple of points in order to get the kind of accuracy in pointing I had the night (or several days) before?  I think the same thing happens if I use the APCC GOTO instead of TheSkyX, but I have only tried this once and was not careful in testing it.  - Dan Price 


 

i wonder if your settings in TSX are somehow a little off compared with APCC.

 On a night's startup you might try removing TSX from the equation, use APCC's and/or SGP to slew and test your settings

if the error is closer to 3-4 arcmin that could be an epoch mismatch



On Thu, Sep 15, 2022 at 6:10 PM Dan R Price <danrprice.ap@...> wrote:
I am having a minor problem with APCC/APPM.  I begin with running APPM for about 30 points, all near the DEC of my target for the evening.  This works just fine.  Once APPM is done I run TheSkyX, find my target, switch over to SGP and run the imaging sequence for several hours.  This works just fine.  I then park the Mach2GTO and power off everything (telescope, computer).  I am very careful not to touch the telescope or mount.  The next evening I power everything up and assume I am good to go.  I run TheSkyX, find my target and slew to it.  I then take a simple image to check location and always find I have an offset of roughly 10 arc minutes from my location the night before.  I then go to APPM and do a Verify for a couple of points.  The Verify says I am .1 arc minutes or better.  At this point I abort the Verify.  I then go back to TheSkyX, do a find on my target and slew to it again.  This time the target position is almost perfect.  The rest of the evening goes smoothly.  My question is - what am I misunderstanding about APPM (or TheSkyX) that requires I run APPM/Verify on a couple of points in order to get the kind of accuracy in pointing I had the night (or several days) before?  I think the same thing happens if I use the APCC GOTO instead of TheSkyX, but I have only tried this once and was not careful in testing it.  - Dan Price 




Dan R Price
 

Thank you, Brian.  I've been using Polaris for testing.  Maybe Polaris is a bad choice for testing the performance of the APPM.  I seem to have come up with more questions and no clear answer.  In Stellarium 0.20.2 it shows for Polaris:
 
(J2000.0):  2h31m51.50s/+89d15m51.5s
(on date):  3h00m08.78s/+89d21m33.9s
 
Could Polaris have changed its location by approximately 28 minutes in just 22 years? 
 
Also, after using Sharpcap to perform a Polar Alignment and then running APPM/Verify for the first three points of the model (worst RA delta was -.273 arc-min, worst DEC delta was .347 arc-min) and then performing another go to to Polaris from TheSkyX, the Astro-Physics V2 ASCOM Driver went from
 
Before:    03:57:43/89:21:38
to 
After:       03:57:27/89:21:37
 
If this is RA/DEC why is it so far off from Stellarium and TheSkyX?  Is it because Polaris is so close to the earth's polar axis?  Do I have something set up wrong?  Also, as expected, another test image now shows Polaris is very close to the exact center of the image.  If it is an Epoch issue then that would mean APPM/Verify caused the Epoch used to be changed?  
 
Just to add another bit of confusion - TheSkyX lists for Polaris Topocentric:  03h02m11.2626s/89d21m16.859s, and 2000.0:  02h31m49.0837s/89d15m50.794s.  I could see confusing the two systems would cause the error, but then why would running APPM/Verify correct it?
 
Is it possible that APPM/Verify is introducing the 18 second difference between GPS and UTC?  And that this 18 seconds is being lost when the mount and computer are being shut down?  

I'll follow your suggestion and see what happens when I take TheSkyX out of the test and only use APCC.  Thank you!
 
Clear Skies,
Dan


 

>>> If this is RA/DEC why is it so far off from Stellarium and TheSkyX?  Is it because Polaris is so close to the earth's polar axis? 

Boy, yes. Polaris is a poor choice for this kind of test for the reason you mentioned. I get all kinds of crazy numbers at polaris that are misleading

I wouldn't take any other action until you can test with a target that is well away from either pole, and preferably well above the horizon 



On Fri, Sep 16, 2022 at 8:46 AM Dan R Price <danrprice.ap@...> wrote:
Thank you, Brian.  I've been using Polaris for testing.  Maybe Polaris is a bad choice for testing the performance of the APPM.  I seem to have come up with more questions and no clear answer.  In Stellarium 0.20.2 it shows for Polaris:
 
(J2000.0):  2h31m51.50s/+89d15m51.5s
(on date):  3h00m08.78s/+89d21m33.9s
 
Could Polaris have changed its location by approximately 28 minutes in just 22 years? 
 
Also, after using Sharpcap to perform a Polar Alignment and then running APPM/Verify for the first three points of the model (worst RA delta was -.273 arc-min, worst DEC delta was .347 arc-min) and then performing another go to to Polaris from TheSkyX, the Astro-Physics V2 ASCOM Driver went from
 
Before:    03:57:43/89:21:38
to 
After:       03:57:27/89:21:37
 
If this is RA/DEC why is it so far off from Stellarium and TheSkyX?  Is it because Polaris is so close to the earth's polar axis?  Do I have something set up wrong?  Also, as expected, another test image now shows Polaris is very close to the exact center of the image.  If it is an Epoch issue then that would mean APPM/Verify caused the Epoch used to be changed?  
 
Just to add another bit of confusion - TheSkyX lists for Polaris Topocentric:  03h02m11.2626s/89d21m16.859s, and 2000.0:  02h31m49.0837s/89d15m50.794s.  I could see confusing the two systems would cause the error, but then why would running APPM/Verify correct it?
 
Is it possible that APPM/Verify is introducing the 18 second difference between GPS and UTC?  And that this 18 seconds is being lost when the mount and computer are being shut down?  

I'll follow your suggestion and see what happens when I take TheSkyX out of the test and only use APCC.  Thank you!
 
Clear Skies,
Dan




Ray Gralak
 

Hi Dan,

Thank you, Brian. I've been using Polaris for testing. Maybe Polaris is a bad choice for testing the performance of
the APPM. I seem to have come up with more questions and no clear answer. In Stellarium 0.20.2 it shows for
Polaris:
APCC disables pointing and tracking rate correction near the pole because there can be wild variations in RA there. So you were not testing pointing correction at all in this case.

-Ray


Dan R Price
 

Brian and Ray, thank you!  I followed your suggestions and used Deneb instead.  Also took TheSkyX out of the test and used the APCC GOTO instead.  Deneb showed up in the center of the image with the first try after powering up.  I then went back to TheSkyX and did a GOTO to Polaris and it showed up in the center as well.  Using TheSkyX performed a GOTO to Vega and then M13.  All showed up in the center of the image.  Looks like there might be a minor issue with the first GOTO after power up if I use TheSkyX.  If the first GOTO is APCC then everything seems to follow just fine.  Again, thank you!