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[Felix Hagemann <679398@xxxxxxxxxxxxxxxxxx>]

With a current snapshot this happens as well. Occurs with portait images
of 2920x4386 when going from 199 degrees to 200 degrees fov. I have
spend a bit of time trying to hunt this bug down. Preliminary result:

1. During image remapping in saRemap.c, saRemap_new(...) x[i] in this line 
y[i] = CamLens_RofA( pd, CamLens_AofR( ps, x[i] ) )
becomes > Pi.
2. Therefore the calls to CamLens_RofA( pd, CamLens_AofR( ps, x[i] ) )  (itself calling a2r_ster which calculates tan(0.5 * x[i] ) returns a negative value for y[i].
3. The negative value for y[i] makes the monoticity test of the following spline evaluation fail, making the whole saRemap_new return 0 and autopano-sift-c segfault when saRemap_inv tries to dereference the null pointer.

Questions:
A comment in CamLens.c indicates that A (or x[i] in the above) should be < Pi for stereographic projection. Does this make sense? How did we end up with it being greater? Why does this trigger at fov > 199 in portrait and >225 in landscape? 
Should we just remap all x > pi to x = pi to get rid of the problem?

Sorry for the chaotic braindump above, I need to go to sleep now and
need to write the stuff down, otherwise a start from scratch is needed
when I'm looking at the problem again.

Regards
Felix

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https://bugs.launchpad.net/bugs/679398

Title:
  autopano-sift-c crashes with very wide photos

Status in Hugin - Panorama Tools GUI:
  Triaged

Bug description:
  With autopano-sift-C 2.5.1

An 8mm fisheye on a full size sensor produces a landscape orientation photo with an angle of view of 260 degrees, calling apsc like this results in no features identified and a segfault:

  autopano-sift-c --projection 2,260 output.pto *.JPG

The transition is sudden: 223, 224, 225 degrees are fine and hundreds of features are detected. 226 degrees and above and 0 features are detected and matching produces a segfault.