Issue

Target 11/16 (NGC 7492) - Guide Run 2
Guiding achieved, but possibly a 'near-miss'
- Overall RMS 2.1" (RA 1.5", Dec 1.4" ), SNR 26, HFD 4.5".
- Guide Request ({"method": "guide", "params": [{"pixels": 2.0, "time": 10, "timeout": 15}, false, [341, 229, 2415, 1622] ], "id": 725} made at 02:14:51
- Guide Initiation was slow, 2 very dim stars (SNR 6) were initially selected but then became lost
- StartPHD2Guiding timed out waiting after 30s (guiding process will be continued in the hope that guiding settles)
- The guide star at 2736.8, 1170.0 with SNR 18 was selected after 39s, and Settling was begun after 40s.
- PHD2 settling timed-out after 56s (16s after SettleBegin) when the SettleDone Event returned the error "timed-out waiting for guider to settle")
- Picture of the GuideFrame below, shows that the ROI for the Find Star operation happened to be devoid of any bright stars.
- The 3 brightest stars in image all lie outside of the ROI.
- Fortunately there are couple of dim stars within the ROI, one of which was selected as the guide star.

- Whilst  initially selected star had a very low SNR (6) which would probably be too low to achieved reliable guiding  PHD2 eventually setlled on a star (with SNR 16)  which held an average SNR of 26 across the imaging interval.

Target 13/16 (AT2021aesn) - Guide Run 4
Guiding largely failed. Stars trailed in at least 3 of 5 images.
- Overall RMS 13.8" (RA 10.1", Dec 9.4") SNS 9, HFD 3.8",  Lost Star frames  84%
- Guide Request {"method": "guide", "params": [{"pixels": 2.0, "time": 10, "timeout": 15}, false, [341, 229, 2415, 1622] ], "id": 960} made at 02:56:54
- Guide Initiation was slow, 2 very dim star (SNR 7) were initially selected but then became lost
- StartPHD2Guiding timed out waiting after 30s (guiding process will be continued in the hope that guiding settles)
- The guide star at 2743.0, 1861.7 with SNR 7, HFD 4.4 was selected after 34s, and Settling was begun after 40s
- Lock Position was reset to 2716.8, 1882.4 after 56s.
- PHD2 settling timed-out after 57s (16s after SettleBegin) when the SettleDone Event returned the error "timed-out waiting for guider to settle".

- Picture of the Reference GuideFrame (10s exp) shown below, shows that the Full Frame and the ROI is completely devoid of any stars (due to cloud).
   (Note.  Capture of the F1 Guide Frame (1.5s exp) failed. Cloud may have partially passed by time of FindStar)
- The selected 'star' had a very low SNR (7) and probably doesn't represent a real star, but just a hotter patch of pixels. Guiding wasn't reliable due to poor/dim guide star and due to cloud.  
- The Y coordinate of selected guide star (1861.7) is unexpected  as it lies outside of the specified ROI where the Y coord of the bottom of the ROI is x(229) + height (1622) = 1851

Target 14/16 (NGC 157) - Guide Run 5
Guiding failed. Stars trailed
- Overall RMS 99.8" (RA 95.0", Dec 30.7") SNS 7, HFD 3.5", Lost Star frames 93%
- Guide Request {"method": "guide", "params": [{"pixels": 2.0, "time": 10, "timeout": 15}, false, [341, 229, 2415, 1622] ], "id": 1041} made at 03:11:53
- Guide Initiation was slow, 2 very dim stars (SNR 6) were initially selected but then became lost
- StartPHD2Guiding timed out waiting after 30s (guiding process will be continued in the hope that guiding settles)
- The guide star at 1438.3, 255.3 with SNR 7, HFD 2.9 was selected after 77s, and Settling was begun after 82s.
- PHD2 settling timed-out after 97s (16s after SettleBegin) when the SettleDone Event returned the error "timed-out waiting for guider to settle")
- Picture of the GuideFrame below, shows that image is largely devoid of stars.

- The brightest star at 1682, 466 and next brightest star at 1629, 1122 both lie within the ROI. In the image the brightest star shows a potential dim 'star' to left of the principal star. This is likely to be a hot pixel or cosmic strike, as there is feature is not present in the earlier 10s reference frame, and may not appear in the frame used by AutoFind Star process.
- Examining the PHD2 debug file, neither of the two brightest stars appears in the AutoFind: local max list. Far less obvious collections of hotter pixels are listed !. This is before any 'star' candidates are excluded.  Both stars appear in an earlier 10s reference image thereby ruling out the possiblity that they were cosmic ray strikes that were not present in the image frame that AutoFind was run against.
- The selected star had a very low SNR (6-7) and proved to be unreliable for guiding (93% of guide frames produced a 'star lost' event).

 It is unclear why one of the brighter stars wasn't selected by autofind, but it seems there weren't even recognised as candidates in the local max. The manual for Camera Settings says that misshapen stars may not be recognised by PHD2's guide star auto-selection.   The manual says that  " 'Auto-selection frame downsample' setting can be used in unusual situations where PHD2 guide star auto-selection is not recognizing misshapen stars. If this happens, you can try values greater than 1 to improve the chances of recognizing such stars".    It is proposed to try out a session setting 'Auto-selection frame downsample' to 3,  and possibly also turn on 'Enable diagnostic image logging' and check  the 'For All Auto-select Star frames' option.

AstroMain Code Tests

AstroMain 3.53.10: New code was added to StartPHD2Guiding() routine so that if the SNR of the star selected by PHD2 Guide Method is too low (<30) the x,y coordinates of the brighest star in the image is identified by GetBrightestObject() and used to change the lock position using the 'set_lock_position' method. Whilst this successfully sets the lock position, as evidenced by a subsequent LockPositionSet event  with the same coordinates that were sent (but notably without a 'StarSelected' event with same/similar coordinates),  this is followed by a new LockPositionSet with totally different coordinates. Problem seems to happen for each guide run where a new guide star tries to be set by StartPHD2Guiding(), there were no guide runs where the intended guide star was actually used for guiding. 

Change made in AstroMain 3.53.11 beta version to use set_lock_position with Exact = false parameter.  (Guide/Manual says "When EXACT is true, the lock position is moved to the exact given coordinates. When false, the current position is moved to the given coordinates and if a guide star is in range, the lock position is set to the coordinates of the guide star").  We can see that using 'set_lock_position' isn't the correct method to use because a)  the currently selected Guide star probably isn't in range of the proposed new lock position and b) if it was in range guide movements would be made to move the guide star to the new lock position.

In the absence of a 'set_guide_star' method,  the most appropriate method to try would seem to be 'find_star', but in order to direct PHD2 it to the required guide star, find_star would be used with roi: [x,y,width,height] that describe a box around the required guide star. 

- Using {"method": "find_star", "params": {"roi": [484, 86, 20, 20]}, "id": 186}   produced error message "could not find star".
- Using {"method": "find_star", "params": {[365, 248, 20, 20]}, "id": 122} causes PHD2 to crash.
- Using {"method": "find_star", "params": [276, 248, 20, 20], "id": 48}  produced error message "invalid ROI param".
- Using {"method": "find_star", "params": {283, 139, 20, 20}, "id": 110}  produced error message "invalid JSON request: Missing name on line 1".
- Using {"method": "find_star", "params": [[285, 136, 20, 20]], "id": 174}  produced error message "could not find star".
- Using {"method": "find_star", "params": [[266, 225, 50, 50]], "id": 235}  produced error message "could not find star".
- Using {"method": "find_star", "id": 46}  (ie entire frame) produced error message "could not find star".
- Using {"method": "find_star", "params": [[472, 65, 50, 50]], "id": 240} outside when capture is stopped causes PHD2 to change guide star corresponding to coordinates of proposed star.  But when guide method is called again, PHD2 goes back to another (dimmer) star.
The method for finding BrightestObject in Image would sometime return coordinates for a star lying outside of the intended ROI area.

In the end (i.e. in the final AstroMain 3.53.11 version) it was decided to rule out the attempt to define and select a new guide star position as it was not a practical solution. 

It remains an option to stop the current guide initiation in the event of a low SNR star and repeat a Guide initiation but using Full Frame instead of the smaller ROI used by design.  This would increase the image area available for finding a candidate guide star by 66%.

Actions

TimeOut. Increase PHD2 Guide TimeOut parameter from 15 to 30s. 
StartPHD2Guiding TimeOut. Increase StartPHD2Guiding's TimeOut from 30s to 100s.
     (This is an initial timeout period but should be adjusted on the fly after seeing SettleBegin)
Auto-selection frame downsample.  Run a session or part of session with Auto-selection frame downsample set to 3 (instead of auto or 1). This is see if it helps improve the chances of PHD2 recognizing 'misshapen' stars.
Guide request.  In event of a low SNR star, repeat the Guide Request using Full Frame rather than the more restrictive ROI initially used. This would increases the area available for finding a candidate guide star by 66%.

Debug Log

PHD2's Debug Log File details each AutoFind attempt

For AutoFind associated with Target 11/16 (NGC 7492), the log file shows

Guide Request at 02:14:51

- Time Ok 02:14:51 (Local)
- Lock Position Ok X 2765.3, Y 1571.7(5.0s) SNR --
- Star Selected Ok X 2765.3, Y 1571.7(5.0s) SNR 6
- Lock ... Fail Lost Lock (8.2s)
- Star ... Fail Star lost (8.2s) Low HFD
- Lock Position Ok X 811.5, Y 216.4 (19.2s) SNR --
- Star Selected Ok X 811.5, Y 216.4 (19.3s) SNR 6
- Lock ... Fail Lost Lock (22.5s)
- Star ... Fail Star lost (22.5s) Low SNR
Guiding ... Info StartPHD2Guiding has timed out after 30s

02:14:51.080 00.003 11704 PhdController::Guide begins
02:14:51.080 00.000 11704 PhdController: newstate STATE_SETUP
02:14:51.080 00.000 11704 PhdController: setup
02:14:51.080 00.000 11704 PhdController: newstate STATE_ATTEMPT_START
02:14:51.080 00.000 11704 PhdController: start capturing
02:14:51.093 00.013 11704 Changing from state SELECTING to UNINITIALIZED
02:14:51.095 00.002 11704 guider state => SELECTING
02:14:51.098 00.003 11704 StartCapturing CaptureActive=0 continueCapturing=0 exposurePending=0
02:14:51.104 00.006 11704 ScheduleExposure(1500,3,0) exposurePending=0
02:14:51.105 00.001 11704 Enqueuing Expose request
02:14:51.105 00.000 11704 PhdController: newstate STATE_SELECT_STAR
02:14:51.111 00.006 11704 evsrv: cli 0AB88D78 response: {"jsonrpc":"2.0","result":0,"id":725}
02:14:51.113 00.002 2700 Worker thread wakes up
02:14:51.113 00.000 2700 worker thread servicing REQUEST_EXPOSE 1500
02:14:51.113 00.000 2700 Handling exposure in thread, d=1500 o=3 r=(0,0,0,0)
02:14:53.112 01.999 2700 Exposure complete
02:14:53.619 00.507 2700 worker thread done servicing request
02:14:53.621 00.002 11704 OnExposeComplete: enter
02:14:53.623 00.002 11704 UpdateGuideState(): m_state=1
02:14:53.624 00.001 11704 UpdateCurrentPosition: no star selected
02:14:53.628 00.004 11704 Throw from C:\cygwin\home\agalasso\projects\phd2\guider.cpp:1352->unable to update current position
02:14:53.628 00.000 11704 Status Line: No star selected
02:14:53.637 00.009 11704 UpdateImageDisplay: Size=(3096,2080) min=1254, max=1595, med=1368, FiltMin=1325, FiltMax=1563, Gamma=0.390
02:14:53.957 00.320 11704 UpdateGuideState exits: No star selected
02:14:53.958 00.001 11704 GuiderMultiStar::AutoSelect enter
02:14:53.962 00.004 11704 Star::AutoFind called with edgeAllowance = 0 searchRegion = 30 roi = 2415x1622@341,229
02:14:53.963 00.001 11704 AutoFind: using ROI 2415x1622@341,229
02:14:54.240 00.277 11704 AutoFind: auto downsample for scale 1.03 => 1x
02:14:54.761 00.521 11704 AutoFind: global mean = -0.0, stdev 202.9
02:14:54.761 00.000 11704 AutoFind: using threshold = 0.1

02:14:55.095 00.334 11704 AutoFind: local max [342, 230] 21.4
  sequence of 'local max'
02:14:55.318 00.000 11704 AutoFind: local max [2754, 411] 13.7

02:14:55.318 00.000 11704 AutoFind: too close [2754, 411] 13.7 - [2754, 400] 13.7
 sequence of too close'
02:14:55.455 00.004 11704 AutoFind: too close [2739, 230] 13.8 - [2754, 230] 21.4

02:14:55.458 00.003 11704 AutoFind: BPP = 16, saturation at 65535, pedestal 0, thresh = 58981
02:14:55.460 00.002 11704 Star::Find(30, 342, 1849, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:55.462 00.002 11704 Star::Find false star n=3 nbg=281 bg=1368.8 sigma=4.7 thresh=1383 peak=1381
02:14:55.462 00.000 11704 Star::Find returns 0 (2), X=342.00, Y=1849.00, Mass=60, SNR=2.9, Peak=1396 HFD=0.0
  sequence of x,y, starmass SNR, Peak, HFD measurements
02:14:55.667 00.000 11704 Star::Find(30, 1959, 230, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:55.678 00.011 11704 Star::Find false star n=9 nbg=275 bg=1369.1 sigma=4.3 thresh=1382 peak=1382
02:14:55.680 00.002 11704 Star::Find returns 0 (2), X=1959.00, Y=230.00, Mass=135, SNR=2.9, Peak=1389 HFD=0.0

02:14:55.682 00.002 11704 AutoFind: finding best star pass 1
02:14:55.682 00.000 11704 Star::Find(30, 342, 1849, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:55.682 00.000 11704 Star::Find false star n=3 nbg=281 bg=1368.8 sigma=4.7 thresh=1383 peak=1381
02:14:55.682 00.000 11704 Star::Find returns 0 (2), X=342.00, Y=1849.00, Mass=60, SNR=2.9, Peak=1396 HFD=0.0
  sequence of x,y SM, SNR, Peak, HFD
02:14:55.901 00.002 11704 Star::Find(30, 1959, 230, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:55.905 00.004 11704 Star::Find false star n=9 nbg=275 bg=1369.1 sigma=4.3 thresh=1382 peak=1382
02:14:55.907 00.002 11704 Star::Find returns 0 (2), X=1959.00, Y=230.00, Mass=135, SNR=2.9, Peak=1389 HFD=0.0
02:14:55.909 00.002 11704 AutoFind: could not find a star on Pass 1

02:14:55.912 00.003 11704 AutoFind: finding best star pass 2
02:14:55.916 00.004 11704 Star::Find(30, 342, 1849, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:55.918 00.002 11704 Star::Find false star n=3 nbg=281 bg=1368.8 sigma=4.7 thresh=1383 peak=1381
02:14:55.920 00.002 11704 Star::Find returns 0 (2), X=342.00, Y=1849.00, Mass=60, SNR=2.9, Peak=1396 HFD=0.0
  short sequence
02:14:55.938 00.003 11704 Star::Find(30, 2754, 1552, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:55.939 00.001 11704 Star::Find returns 1 (0), X=2765.32, Y=1571.68, Mass=110, SNR=5.9, Peak=1405 HFD=3.6
02:14:55.943 00.004 11704 AutoFind: star saturated or too dim [2754, 1552] 13.8 Mass 110 SNR 5.9

02:14:55.943 00.004 11704 AutoFind: star saturated or too dim [2754, 1552] 13.8 Mass 110 SNR 5.9
02:14:55.944 00.001 11704 Star::Find(30, 468, 1849, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:55.944 00.000 11704 Star::Find false star n=3 nbg=276 bg=1368.0 sigma=4.7 thresh=1382 peak=1378
02:14:55.951 00.007 11704 Star::Find returns 0 (2), X=468.00, Y=1849.00, Mass=44, SNR=2.9, Peak=1386 HFD=0.0


02:14:56.128 00.000 11704 AutoFind: could not find a non-saturated star!
 
02:14:56.144 00.016 11704 AutoFind: finding best star pass 3
02:14:56.146 00.002 11704 Star::Find(30, 342, 1849, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:56.147 00.001 11704 Star::Find false star n=3 nbg=281 bg=1368.8 sigma=4.7 thresh=1383 peak=1381
02:14:56.147 00.000 11704 Star::Find returns 0 (2), X=342.00, Y=1849.00, Mass=60, SNR=2.9, Peak=1396 HFD=0.0
 Sequence of Stars
02:14:56.162 00.000 11704 Star::Find(30, 2754, 1552, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:56.162 00.000 11704 Star::Find returns 1 (0), X=2765.32, Y=1571.68, Mass=110, SNR=5.9, Peak=1405 HFD=3.6
02:14:56.162 00.000 11704 AutoFind returns star at [2754, 1552] 13.8 Mass 110 SNR 5.9

PHD2 reports  Star Selected   X 2765.3, Y 1571.7(5.0s) SNR 6

02:14:56.162 00.000 11704 MultiStar: primary star forcibly inserted in list
02:14:56.162 00.000 11704 Star::Find(30, 2754, 1552, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:56.175 00.013 11704 Star::Find returns 1 (0), X=2765.32, Y=1571.68, Mass=110, SNR=5.9, Peak=1405 HFD=3.6
02:14:56.177 00.002 11704 MultiStar: List (1): {2765.32, 1571.68}(5.9),
02:14:56.179 00.002 11704 setting lock position to (2765.32, 1571.68)
02:14:56.179 00.000 11704 MultiStar: stabilizing after lock position change
02:14:56.179 00.000 11704 AutoSelect: state = 1, call UpdateGuideState
02:14:56.179 00.000 11704 UpdateGuideState(): m_state=1
02:14:56.179 00.000 11704 Star::Find(30, 2765, 1571, 0, (0,0,0,0), 2.5, 65535) frame 1
02:14:56.193 00.014 11704 Star::Find returns 1 (0), X=2765.32, Y=1571.68, Mass=110, SNR=5.9, Peak=1405 HFD=3.6

Update 2022-09-12
Issue resolved in session S1036 by reducing Minimum SNR from 50 to 13.  This now allows PHD2's Find Star to select a guide star is range 13 to 49 which were previously been overlooked in favour of dim star/noise with SNR of only 6 or 7 ('strange but true').