Object database coordinates not accurate

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astrosatch
Posts: 18
Joined: Tue Sep 25, 2018 7:46 am

Object database coordinates not accurate

Post by astrosatch » Thu May 16, 2019 7:07 am

Hi!
I'm using ASIAIR with EQmod and when I choose object from database it doesn't come into center. Even multiple platesolving doesn't help. So I checked coordinates in Skysafari and are different. Then I manually put coordinates from skysafari and the object ends in center. I'm not sure how many objects are incorect, but I noticed more than one. Ngc 4038 is off by several minutes. This should be corrected, because otherwise object list is useless and one should do better with manually entering coordinates from Skysafari.

Br,
Andrej

lancer jiang
Posts: 74
Joined: Mon Nov 26, 2018 9:59 am

Re: Object database coordinates not accurate

Post by lancer jiang » Thu May 16, 2019 9:18 am

Hi Andrej
I got the same RA&Dec,the same altitude,etc..by my AIR and SkySafari,please check the screenshot attached.

Here‘s my step
1. AIR: choose object-> search ngc 4038
2. SkySafari 5 pro ->Search ngc 4038

12345.png

mAnKiNd
Posts: 14
Joined: Tue Feb 20, 2018 3:29 am

Re: Object database coordinates not accurate

Post by mAnKiNd » Fri May 17, 2019 2:30 am

astrosatch wrote:
Thu May 16, 2019 7:07 am
Hi!
I'm using ASIAIR with EQmod and when I choose object from database it doesn't come into center. Even multiple platesolving doesn't help. So I checked coordinates in Skysafari and are different. Then I manually put coordinates from skysafari and the object ends in center. I'm not sure how many objects are incorect, but I noticed more than one. Ngc 4038 is off by several minutes. This should be corrected, because otherwise object list is useless and one should do better with manually entering coordinates from Skysafari.

Br,
Andrej

I can report I am experiencing a similar issue.

Right now, NGC 7023 (Iris Nebula) is not agreeing with Sky Safari 6 Pro pointing.

The target slew was initiated in ASIAIR and subsequently centered by three plate solving and sync attempts, but the target did not end up in the centre of the crosshair (it was relatively close) so I followed it up with some manual mount adjustments until it was good enough.

Following this, switching to SS6 revealed that the pointing frame was showing way off after the ASIAIR plate solve and sync! I even tried hitting align in SS6 after plate solve and sync in ASIAIR and SS6 is stating "command failure...too far from telescope's actual position".

Furthermore, RA+DEC coordinates for the Iris Nebula do NOT agree between the two apps, they have slightly different values, which is most probably why this issue exists.

Please advise?

Using EQMOD with AZ-GTi on Android.

Hope this helps.
Minos

astrosatch
Posts: 18
Joined: Tue Sep 25, 2018 7:46 am

Re: Object database coordinates not accurate

Post by astrosatch » Mon Jul 08, 2019 9:47 am

There still isn't correction in asiair database. I can definatelly say that coordinates of all objects including star database are wrong. For cca 5 arc minutes. Not single one ends in center. On the other hand, coordinates from Skysafari are all accurate. Please correct this.

Br,
Andrej

W7AY
Posts: 54
Joined: Fri Jan 25, 2019 3:38 am

Re: Object database coordinates not accurate

Post by W7AY » Mon Jul 08, 2019 5:28 pm

>> There still isn't correction in asiair database.

I wonder if the ASIAIR is not using the current precession Epoch (JNOW), and instead sticking with the year 2019.5 that many databases start with before epoch conversion. In the example shown by Mr. Jiang, he had compared the ASIAIR coordinates with the 2019.5 info in SkySafari.

However, in SkySafari, there is a way for the user to ask the app to convert to whatever epoch (current epoch checkbox == JNOW). We don't know what epoch ASIAIR uses.

I just checked SkySafari with Kochab. With the reference 2019.5 epoch, the SkySafari object database shows a declination for Kochab of 74 deg 4' 39". When I slewed to Kochab using J2000, SkySafari showed 74 deg 9'. When I chose JNOW (current epoch), SkySafari showed 74 deg. 5'. There is significant differences in 20 years.

In addition to precession, there is also the proper motion of the stars (also shown in the SkySafari object database). But those are relatively small compared to precession changes. So I don't think that is the error that you found with ASIAIR.

On top of that, there is atmospheric refraction (which affect stars closer to the horizon), but since I was earlier told that the ASIAIR corrects for it in the polar alignment process, ZWO is probably also accounting for it in GOTO.

Jiang xian sheng: could you please check with your team what Epoch is used when converting the original star database to the true star position? If the current Epoch (JNOW) is not used, that can also affect the accuracy of calculating the NCP during polar alignment, .

Clear skies,

Chen

lancer jiang
Posts: 74
Joined: Mon Nov 26, 2018 9:59 am

Re: Object database coordinates not accurate

Post by lancer jiang » Wed Jul 10, 2019 5:45 am

Hi Mr.Chen
“Jiang xian sheng: could you please check with your team what Epoch is used when converting the original star database to the true star position? If the current Epoch (JNOW) is not used, that can also affect the accuracy of calculating the NCP during polar alignment,”
Yes,confirmed with R&D,the JNOW is used currently.

astrosatch
Posts: 18
Joined: Tue Sep 25, 2018 7:46 am

Re: Object database coordinates not accurate

Post by astrosatch » Thu Jul 11, 2019 11:49 am

" Yes,confirmed with R&D,the JNOW is used currently "

So what is wrong then? I just don't have the same coordinates and my Skasafari epoch is Jnow.

astrosatch
Posts: 18
Joined: Tue Sep 25, 2018 7:46 am

Re: Object database coordinates not accurate

Post by astrosatch » Mon Jul 15, 2019 10:10 am

Here are my coordinates in Asiair 1.2 latest beta

NGC 4038
RA 12h2.63 DEC -18deg 51.85'

Iancer jiang, how is possible that they aren't the same in your app?

W7AY
Posts: 54
Joined: Fri Jan 25, 2019 3:38 am

Re: Object database coordinates not accurate

Post by W7AY » Mon Jul 15, 2019 7:48 pm

Hi astrosatch,

That is really odd.

On my iPad (iOS 12.3.1) running ASIAIR Beta 6, I am getting this for NGC 4038 (I am just testing, not a ZWO employee).

RA 12h 2m 52s (12h 2.8667m) and DEC -18º 58' 23" (-18º 58.38').

The DEC is *substantially* different from the DEC that you see (-18º 51.85').

For what its worth, the JNOW RA and DEC that SkySafari estimates are

RA 12h 2.87m and DEC -18º 58.38'.

The displayed numbers for my copy of ASIAIR and my copy of SkySafari 6 Plus are virtually identical. But both are different from your beta ASIAIR. Are you using iOS? If not, perhaps that is the difference?

Regards,
Chen

astrosatch
Posts: 18
Joined: Tue Sep 25, 2018 7:46 am

Re: Object database coordinates not accurate

Post by astrosatch » Tue Jul 16, 2019 7:20 am

Chen: The displayed numbers for my copy of ASIAIR and my copy of SkySafari 6 Plus are virtually identical. But both are different from your beta ASIAIR. Are you using iOS? If not, perhaps that is the difference?

I am using android. However this shouldn't be the reason. Just because I'm not using IOS, the objects are not in different area of the sky. I wonder if other android users notice this.

Andrej

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