I'm using INDI Library 1.8.5 ; Kstars 3.4.2 ; Source: PPA ; Kernel/Arch : 5.4.0-40-generic #44-Ubuntu SMP Tue Jun 23 00:01:04 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux.
My mosaics that are 1W x 2H have correct overlap, however my 2W x 1H have more overlap - about 30% instead of 5%.
The maths seems to check out OK when looking at the calculated RA/DEC for the panels, but there is a big overlap for some reason.
This can be recreated using the simulator CCD.
I created an example using NGC5139, simulator CCD (1280x1024, 5.2um pixel) with a 480mm FL scope. FOV is 47.67' x 38.14'.
For the example I set a 2Wx1H mosaic with zero overlap, I expect difference between the panels to be 47.67', the width of the FOV.
The tool created 2 jobs:
(1) RA 13h 28m 20.77s DEC -47° 28" 39.59'
(2) RA 13h 25m 10.09s DEC -47° 28" 39.59'
The difference in RA is 3m 10.68s which is 47.67 arcmin, which is what I expected.
There is no difference in DEC, also as expected.
However, in real world use with my Canon DSLR and also evident here using the simulator CCD dimensions and viewing the RA/DEC for each panel in Stellarium, there is a big overlap between panels.
My maths may be wrong - I certainly not an expert at this, I initially thought it was a bug with the tool but I'm scratching my head as to why the panels overlap so much. As mentioned earlier, this only affects panels along the width of the mosaic, not its height.
I calculated the same 2Wx1H mosaic of NGC5139 layout using Telescopius. Interestingly it generated :
Pane, RA, DEC, Position Angle (East)
PANE 1, 13hr 29' 07", -47º 28' 46", 0
PANE 2, 13hr 24' 27", -47º 28' 46", 0
These are 4' 40" apart in RA. Compared to 3' 10.7" apart from the Ekos tool. The Telescopius panels line up correctly when checked in Stellarium.
As the DEC calculations are OK, I wonder if the issue relates to the difference in units used between RA and DEC - maybe the code behind the tool is treating these the same where they should be different?
Thank you for the detail investigation. This indeed appears to be a bug but I didn't have enough time to investigate it. Maybe you can spot the issue
? This is where it's calculating the center points for each mosaic panel.
My maths or coding isn't good enough for this sorry. I did manage to recreate the calculations in Excel using the method from mosaic.cpp and found I got the wrong RA value as well.
I can say adding the width of the sensor, minus overlap (in degrees) to the RA position (degrees) gives the wrong position, though this method works for DEC.
I had a look at how
do their mosaic tool ((
) and they do some spherical and cartesian coordinate conversion - perhaps that's a hint for you.
I'll keep giving it some thought, and hopefully someone can assist.
RA is in hours, but yeah it's more likely to do with spherical trig. The calculation in Mosaic assumes a flat plane which is only approximate for very small angles and breaks down over large areas. Will have to look at it more in the future unless someone wants to step it to fix that.
I haven't yet used the mosaic tool (but soon will). Big Noel, I'm curious whether you've tried to mosaic at the celestial equator (Dec=0). Is the answer correct at Dec=0? If so, could this be a simple issue with not correctly factoring cos(dec) in the RA calc? The error for NGC5139 is suspicious in this regard.... Just a thought.
Good test dmsummers and you might be on to something.
I'll test Kstars more tomorrow night, but knowing the EKOS tool gives a 3' 10" difference in RA using the simulator when using NGC5139 as a test (DEC -47 28 36). I compared that to the Telescopius results, at RA 0, DEC 0, the difference in RA between centers of a 2x1 mosaic using the SimulatorCCD specs is... 3' 10" !
I entered a different target in Telescopius; RA 0, DEC 45. The difference in centers is 4' 28" . Clearly the Telescopius algorithm is factoring in something relating to the DEC. This might be enough for someone to solve the issue.
When it works, the mosaic tool and scheduler is magic, I really hope to see this issue fixed so I can use it more! AstroPixelProcessor does a good job at compiling the mosaic too.
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