[ptx] libsift control points

[Eric Engle]

Hello,

I have two questions about the libsift/autopano routines.  This seems to
be the audience to address.

I downloaded autopano 1.7 and put it to use on three large grayscale
images with about 30% overlap between neighbor images.  The sift control
points produced looked good at casual inspection (i.e. the hugin control
points tab revealed what looked like excellent correlation between the
three images.)

The resulting mosaic from hugin was terrible.  I spent some time
wrestling with the hugin parameters.  The best image produced is still
badly aligned and warped.

So I backed up and took a closer look at the control points.  I did a
pixel-level comparison between features present in both images and found
that the control points were NEAR the same features but were between 5
and 15 pixels translated.  Unfortunately, the degree and direction of
translation is different at each control point.

Is this likely to be the cause of my bad output from hugin?  Is this an
expected result from the SIFT algorithm?

The images are snapshots of the Martian surface.  They are at slightly
different contrast levels since the satellite took them during different
orbits.  The field of view is extremely narrow, 3-4 degrees.

Could these qualities cause the slight inaccuracies I'm seeing?

Any help here would be appreciated.  I can post the images if they are
needed.

Thanks,
Eric Engle
ASU Mars Space Flight Facility