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25 Jul 2018
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TOPIC: [Fixed] Plate solving giving wrong results with ANSVR

[Fixed] Plate solving giving wrong results with ANSVR 1 week 6 days ago #29494

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I'm running Kstars 2.9.8 on Window 10 64 bit. Platesolving through Ansvr.
My target was NGC6822 (Barnards Galaxy) at (from KStars):
JNow: 19h 45m 58s -14° 45' 45"
J2000: 19h 44m 56s -14° 48' 23"
I get a successful solve and the mount slews. The next solve says it is within acceptable range.
But if I then take an image and solve at nova.astrometry.net it is around 15 arc-minutes off in RA.
Results from nova.astrometry.net (J2000) are:
Center (RA, Dec): (295.932, -14.862)
Center (RA, hms): 19h 43m 43.610s
Center (Dec, dms): -14° 51' 44.593"
Size: 38.1 x 28.8 arcmin
Radius: 0.398 deg
Pixel scale: 1.96 arcsec/pixel
Orientation: Up is 262 degrees E of N
I suspect the conversion of J2000 returned by nova.astrometry.net to JNOW is in the wrong direction. Perhaps as I'm in the southern hemisphere?
Had the same issue with 2.9.6 the other day which is why I upgraded.

Attaching Kstars log and image solved on nova.astrometry.net
Attachments:

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Ubuntu 16.04 AMD64 VM, RPi3 Ubuntu Mate 16.04, Windows 10 AMD64, Ubuntu 16.04 AAEON UP Core
Avalon M-Uno, EQ6 Pro, Atik420, ASI1600MM-C, ASI120MM-S, DBK21AU04, ZWO EFW, Optec TCFSi
Vixen R150S, GSO RC8, ST80
Last Edit: by kengs.

Plate solving giving wrong results 1 week 6 days ago #29496

Hi kengs,

I believe this is good question for Dustin Lang (the author) of astrometry.net --- either as an github
issue or a astrometry.net forum post.

I am not mistaken, then the astrometry.net web engine uses this generic parameter for solving:
solve-field --downsample 2 --tweak-order 2 --scale-units degwidth --scale-low 0.1 --scale-high 180.0

This is what I get, when I solve the image locally under Linux with the latest astrometry.net (master)

Field 1: solved with index index-4205-07.fits.
Field 1 solved: writing to file /tmp/Barnard.solved to indicate this.
Field: Barnard.jpg
Field center: (RA,Dec) = (295.931792, -14.862427) deg.
Field center: (RA H:M:S, Dec D:M:S) = (19:43:43.630, -14:51:44.739).
Field size: 38.1293 x 28.8327 arcminutes
Field rotation angle: up is -82.5227 degrees E of N
Field parity: pos
Creating new FITS file "Barnard_wcs.fit"...

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Plate solving giving wrong results 1 week 6 days ago #29510

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astrometry.net is doing the right thing. It returns coordinates in J2000 which Ekos converts to JNOW. Its the conversion to JNOW that appears to be wrong so the corrective slew to target is taking the target further away from the centre of the field instead of closer to it.

Added: I also solved locally and got the same result as online.

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Ubuntu 16.04 AMD64 VM, RPi3 Ubuntu Mate 16.04, Windows 10 AMD64, Ubuntu 16.04 AAEON UP Core
Avalon M-Uno, EQ6 Pro, Atik420, ASI1600MM-C, ASI120MM-S, DBK21AU04, ZWO EFW, Optec TCFSi
Vixen R150S, GSO RC8, ST80
Last Edit: by kengs.

Re:Plate solving giving wrong results 1 week 5 days ago #29533

That may sound stupid and I do not suggest it could be the case in your test, but I need to mention that I had very weird results when I forgot to suspend guiding while plate-solving. Guiding corrections actually offset the mount model. PHD2 has an option to disable guiding while the mount slews, the internal guider does not.

-Eric

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Plate solving giving wrong results 1 week 5 days ago #29534

Looking at the log, it seems to me we're dealing with an API change here:
[2018-09-12T21:59:09...][     org.kde.kstars.ekos.align] - "{\"jobs\":[62],\"processing_finished\":\"1\",\"processing_started\":\"1\",\"user\":\"0\",\"user_images\":[]}"
[2018-09-12T21:59:09...][     org.kde.kstars.ekos.align] - "{\"status\":\"success\"}"
[2018-09-12T21:59:09...][     org.kde.kstars.ekos.align] - "{\"dec\":\"-14.816192073\",\"epoch\":\"JNow\",\"orientation\":97.5146272814133,\"parity\":1,\"pixscale\":1.96562592485983,\"ra\":\"296.199887826\",\"radius\":0}"

RA/DEC seem to be returned in JNow here.
-Eric

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Re:Plate solving giving wrong results 1 week 5 days ago #29535

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TallFurryMan wrote: That may sound stupid and I do not suggest it could be the case in your test, but I need to mention that I had very weird results when I forgot to suspend guiding while plate-solving. Guiding corrections actually offset the mount model. PHD2 has an option to disable guiding while the mount slews, the internal guider does not.

-Eric

I was using PHD2 but guiding was off. I re-ran the platesolve under controlled conditions.

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Ubuntu 16.04 AMD64 VM, RPi3 Ubuntu Mate 16.04, Windows 10 AMD64, Ubuntu 16.04 AAEON UP Core
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Plate solving giving wrong results 1 week 5 days ago #29537

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TallFurryMan wrote: Looking at the log, it seems to me we're dealing with an API change here:

[2018-09-12T21:59:09...][     org.kde.kstars.ekos.align] - "{\"jobs\":[62],\"processing_finished\":\"1\",\"processing_started\":\"1\",\"user\":\"0\",\"user_images\":[]}"
[2018-09-12T21:59:09...][     org.kde.kstars.ekos.align] - "{\"status\":\"success\"}"
[2018-09-12T21:59:09...][     org.kde.kstars.ekos.align] - "{\"dec\":\"-14.816192073\",\"epoch\":\"JNow\",\"orientation\":97.5146272814133,\"parity\":1,\"pixscale\":1.96562592485983,\"ra\":\"296.199887826\",\"radius\":0}"

RA/DEC seem to be returned in JNow here.
-Eric

As far as I understand it, astrometry.net returns only J2000 coordinates. I've not found any option to return JNOW coordinates.
I tested again today on another target and Ekos consistently puts the target some 15' off centre in RA. I then switched to Astrotortilla using the same engine and it correctly centred the object.

What I suspect now is that the J2000 to JNOW conversion is being applied twice. Astrometry.net returns RA of 19h43m44s as J2000 which converts to JNOW of 19h44m48s which is the value in the log (296.199887826 degrees). A further J2000 to JNOW conversion is then applied to 19h44m48s which results in 19h45m50s as shown in the next part of the log. 1m of RA corresponds to 15 arcminutes which is the error I am seeing.

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Ubuntu 16.04 AMD64 VM, RPi3 Ubuntu Mate 16.04, Windows 10 AMD64, Ubuntu 16.04 AAEON UP Core
Avalon M-Uno, EQ6 Pro, Atik420, ASI1600MM-C, ASI120MM-S, DBK21AU04, ZWO EFW, Optec TCFSi
Vixen R150S, GSO RC8, ST80

Plate solving giving wrong results 1 week 5 days ago #29538

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Looks like JNOW is an ANSVR config option which is why I couldn't find it in the astrometry.net API documentation. I'll see how to switch it off an hopefully then the solves will work.
The following user(s) said Thank You: TallFurryMan

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Ubuntu 16.04 AMD64 VM, RPi3 Ubuntu Mate 16.04, Windows 10 AMD64, Ubuntu 16.04 AAEON UP Core
Avalon M-Uno, EQ6 Pro, Atik420, ASI1600MM-C, ASI120MM-S, DBK21AU04, ZWO EFW, Optec TCFSi
Vixen R150S, GSO RC8, ST80

Plate solving giving wrong results 1 week 4 days ago #29552

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SOLVED!! (excuse the pun)
Altering the ANSVR config to return J2000 coordinates fixed the issue. I must have set it to JNOW once when messing around with SGP on Windows.
The following user(s) said Thank You: knro

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Ubuntu 16.04 AMD64 VM, RPi3 Ubuntu Mate 16.04, Windows 10 AMD64, Ubuntu 16.04 AAEON UP Core
Avalon M-Uno, EQ6 Pro, Atik420, ASI1600MM-C, ASI120MM-S, DBK21AU04, ZWO EFW, Optec TCFSi
Vixen R150S, GSO RC8, ST80
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