Star Alignment fails with Singular Condition

[georg.viehoever]

See attached log. Sure a minor issue...
Georg

Code: [Select]

StarAlignment: Global context
Loading reference image:
E:/Benutzer/Oeffentlich/Pictures/2010_08_12_Amerika_Astro/2010_09_01_grand_canyon/Calibrated/debayer/debayer_milkywaynorthb10_c.fit
Reading FITS: 32-bit floating point, 3 channel(s), 3908x2602 pixels: 100%
Extracting CIE L* component: 100%
Structure map: 100%
Detecting stars: 100%
12088 stars found.

Registering target image 1 of 17
Loading target file:
E:/Benutzer/Oeffentlich/Pictures/2010_08_12_Amerika_Astro/2010_09_01_grand_canyon/Calibrated/debayer/debayer_milkywaynorthb10_c.fit
Reading FITS: 32-bit floating point, 3 channel(s), 3908x2602 pixels: 100%
Extracting CIE L* component: 100%
Structure map: 100%
Detecting stars: 100%
12088 stars found.
Matching stars ...
* Reference image: Limiting to 2000 brightest stars.
* Target image: Limiting to 2000 brightest stars.
2000 putative star pair matches.
Performing RANSAC ...
2000 star pair matches in 1 RANSAC iterations.
Summary of model properties:
Inliers     : 1.000
Overlapping : 1.000
Regularity  : 0.995
Quality     : 0.999
Root mean square error:
?RMS  :  0.000 px
Average RMS error deviation:
?RMS  :  0.000 px
Peak errors:
?xmax :  0.000 px
?ymax :  0.000 px
Transformation matrix:
     +1.0000     +0.0000     +0.0000
     -0.0000     +1.0000     -0.0000
     -0.0000     +0.0000     +1.0000
scale    : 1.000
rotation :     +0.00°
dx       :     +0.00 px
dy       :     -0.00 px
*** Error: Singular matrix in 2-D surface spline generator

*** Applying error policy: Ask on error...

[Juan Conejero]

Yes, I know this problem. It happens sometimes (rarely) when two or more alignment stars are very close and surface splines are being used as the registration model. Try to change anything that varies the distribution of alignment stars, for example a parameter of the star detection group. A slight variation in the set of alignment stars normally suffices to fix the problem.

This problem is difficult to solve, but I am working on it. I'll try to fix it definitely in the next version. Sorry!

[NKV]

This problem is difficult to solve

difficult... Juan, just add exclusion:

Code: [Select]

If ( reference != target ) target.align();

[georg.viehoever]

This problem is difficult to solve

difficult... Juan, just add exclusion:

Code: [Select]

If ( reference != target ) target.align();

Yes, that should do the trick in 99.999% of all cases....

[Juan Conejero]

If ( reference != target ) target.align();

Yes, the above condition will fix many practical problems. However, instead of the above, I prefer this one:

if ( registration transformation is not identity to within 0.005 px )
   align target
endif

which will prevent failure in even more cases. There will be still some marginal cases where surface spline interpolation will fail due to degenerate configurations of alignment stars. I'll try to fix these also in the next version.