David's Astronomy - Notes 2022-11-25 (S1062)

Backgound
The primary and secondary scope alignment has previously been synced using an Orion X-Y Finder on the back of the secondary scope, and can be checked by examining Guide Reference JPG Pictures which show the plate-solved position of the FOV from LX200 primary scope drawn on to plate solved larger FOV from the secondary scope.

The Scope 2 Pointing Offset from Scope 1 has consistently been < 1' in recent sessions.

Issue

a) S1062 (2022-11-27)

Guide Reference JPG Pictures show a disinct discrepency in the apparent alignment of primary & secondary scopes for the 3rd & 4th target acquired (18:34)
b) S1063 (2022-11-28)

Linking of Cam2 Guide Reference for Target 9/41 (SS Cyg) reported an incorrect Scope2 Offset (20:20)

Description

a) S1062 (2022-11-27)

Targets 2/39 and 3/39 (C/2022 E3 (ZTF) & NGC 6701) showed the expected close alignment in FOV centres (see Fig 2), but beginning with Target 4/39 (GCVS SS Cyg) the alignment appears to have been lost (see Fig 3).

Figure 2. Normal FOV Offset (NGC 6701, 18:17)

Fig 3. False FOV Offset (GCVS SS Cyg, 18:39)

Had the secondary scope lost its close alignment with the main scope ? Had there been a shift in LX200's Primary Mirror (best focus changed dramatically since last session, but alignment between the FOV of the two telescope is ok for first) or was there some slippage in the X-Y Finder 'on the Secondary Scope. FOV. Target 5/40 (29P Schwassmann-Wachmann) also seemed to have poor alignment, but the discrepency was in the opposite direction. Target 6/40 was missed.

Target 7/40 (NGC 7501) and Target 8/40 (M31 w/AT2022icc) and Target 9/40 (GCVS BL Lac) however all showed the expected normal close alignment between the two scopes
b) S1063 (2022-11-28)

Target 3/40 (DY Per) and 9/41 (SS Cyg) reported an incorrect Scope2 Offset of 81.30' and 86.11' respectively and the resulted in Cam1 FOV not being drawn on the Guide_Ref JPG Pictures from these two targets. Other targets had correct Scope 2 offsets and showing the Cam1 FOV area as expected. .. Whilst correct RA/Dec coordinates were reported following linking Guide_Reference image with ASTAP the reported Scope 2 Offset (86.11') is incorrect. This lead to Cam1 FOV not being drawn on the Guide_Ref JPG Picture. The same problem also affected Target 3/40(DY Per, Scope2 Offset 81.30'). It also affected SS Cyg target during the previous S1062 session (2022-11-25)

Analysis

a) S1062 (2022-11-27)

Investigating images from Target 4/39 (GCVS SS Cyg) shows that the Guide Reference taken through TS80 secondary scope shows close alignment on the preceeding final Locate frame taken through LX200 primary scope. This shows that for some reason the LX200 FOV is incorrectly drawn onto the Guide Reference JPG picture.

Final Locate Frame plate solved in TheSky6 (UCA/USNO, Stars 51, Scale 1.403, Angle 179.6°) had a pointing error of just 0.16' and plate-solved coordinates of
    21 42 47.657 (RA J2000),    +43 35 10.69 (Dec J2000)
Guide Reference Frame plate solved in ASTAP (Stars 52, Scale 1.013, Angle 359.1°) had coordinates
    21 42 46.711 (RA J2000),    +43 34 17.48 (Dec J2000)
Scope2 Offset was reported as being 19.64' (N: -7.96', W: 17.96'), compared to normal offset from previous target of only 0.86' (N: -0.86', W: 0.10')
The offset seen in the JPG pictures is evidently associated with this reported Scope 2 Offset, however the difference in the reported plate-solved coordinates corresponds to an actual offset of only , N: -0.86' / W : 0.17' which is consistent with visually close match between the two images and the normal Scope 2 offset. There is clearly a bug or glitch of some kind.

Target 5/40 has a reported Scope2 Offset of 11.08' (N: 6.00', W: -9.31'). Log files don't provide any detail on the calculation, so code will to be replayed using original images to try to understand issue.

Replaying SS Cyg images on Development Computer gave the following

Final Locate Frame wouldn't solve in TheSky6 for some reason, but linked in ASTAP linstead (Stars 0, Scale 1.403, Angle 179.4°)
    21 42 47.652 (RA J2000) +43 35 10.66 (Dec J2000)
Guide Reference Frame plate solved in ASTAP   (Stars 0, Scale 1.013, Angle 359.1°)
   21 42 46.711 (RA J2000) +43 34 17.48 (Dec J2000)
Scope2 Offset was reported as being 0.90' (Offset N: -0.88', Offset W: 0.17'). This time the offset and the result JPG picture are correct (see Fig 4).

Fig 4. Correct FOV Offset (GCVS SS Cyg, 18:39)
(Jpg created from replayed target on Development Computer using original images)

Next step is to examine code and potentially replay the target + original image using debugger to investigate how a glitch could have created an incorrect Scope 2 offset result during the live operation.

Code shows that Scope 2 Offset is calculated in LinkCam2GuideFrame() routine using the equation
    Offset_Mins = AngularSeparation2(LocateInfo2.CenterRa, LocateInfo2.CenterDec, LocateInfo.CenterRa, LocateInfo.CenterDec, dOffsetN, dOffsetW) * 60

AngularSeparation2() is a program routine that doesn't rely on 3rd party library or program and would always be expected to give the correct Offset between the two CenterRa/CenterDec values supplied.

Extra Trace lines added to LinkCam2GuideFrame() in AstroMain 3.58.5 to help diagnose the problem further.
b) S1063 (2022-11-28)

Tracing helped confirmed that correct RA/Dec coordinates were being reported following linking the Guide_Reference image with ASTAP
and confirmed that the coordinates (used for LocateInfo2 (Cam2) were being set by the results of the following code line
   RaDec = Image.XYToRADec(Image.Width / 2, Image.Height / 2)    LocateInfo2.CenterRa = RaDec(0)    LocateInfo2.CenterDec = RaDec(1)
This is ok for images that have been imaged link in TheSky6 and have a valid WCS Inserted, and indeed work for some ASTAP Linked Images. Bit is doesn't evidently work correctly for all ASTAP linked images.   This is not because of what ASTAP is doing but whether an initial call to Image.InsertWC (only designed to place the image into TheSky6 was producing a valid WCS Insert or not.

It had been thougt that exception to Image.XYToRADec would have led to setting to the LocateInfo2(Cam2) coordinates being set by code in exception block using the code
   LocateInfo2.CenterRa = SavedBestRa2000    LocateInfo2.CenterDec = SavedBestDec2000

but this assumption was incorrect.

Issue fixed in AstroMain 3.58.6, by using a new variable 'SavedBestFromASTAP' (boolean) and makes changes to PlateSolveImage() and LinkCam2GuideFrame(), so that if 'SavedBestFromASTAP' = True the LocateInfo2 coords are taken from SavedBestRa2000 and SavedBestDec2000

If SavedBestFromASTAP = True Or SavedWCSisValid = False Then ' added condition 2022-11-27 (MI S1063) ' Get Centre Ra/Dec from SavedBest Coordinates ' ------------------------------------------- ' Note: this to fix issue that some Cam2 images end up giving an incorrect Scope2 Offset    LocateInfo2.CenterRa = SavedBestRa2000    LocateInfo2.CenterDec = SavedBestDec2000    bWorkingWcs = False End If

Conclusion
Any combination of occasional data related conditions and a flaw in log in AstroMain code led to the situation where incorrect coordinates from Cam2 image was being given to the routine that calculates the offsets between the primary and secondary scope, and led to situation where Cam1 FOV was incorrectly position on the Guide Reference JPG picture or was missed of the picture all together.

Issue has been fixed in AstroMain 3.58.6 which is being used in live session S1064 (2022-11-28).


	Session Aims & Highlights
	- Observing Result - Night Summary Plot - Session Event Log

	Operational Issues
	- Critical Issues (0), Major Issues (1), Minor Issues (5), Small Defects (4), Continuous Improvement (10)

	Investigation - Incorrect Scope 2 Offset leading to Incorrect/Missing Cam1 FOV on Guide Reference pictures

	Images from 2022-11-25 >> [ Local Files >> ]

This Web Page:	Notes - Session 1062 (2022-11-25)
Last Updated :	2024-03-27
Site Owner :	David Richards
Home Page :	David's Astronomy Web Site

David's Astronomy Pages
Notes - Session 1062 (2022-11-25)

Session Aims & Highlights (2022-11-25)

Operational Issues (2022-11-25, S1062)

Investigation - Incorrect Scope 2 Offset and Incorrect/Missing Cam1 FOV on Guide Reference pictures

David's Astronomy Pages Notes - Session 1062 (2022-11-25)

Session Aims & Highlights (2022-11-25)

Operational Issues (2022-11-25, S1062)

Investigation - Incorrect Scope 2 Offset and Incorrect/Missing Cam1 FOV on Guide Reference pictures

David's Astronomy Pages
Notes - Session 1062 (2022-11-25)