[ptx] Conserving verticals with many control points

[Damien Douxchamps]

Hi all,

First post here, so hello again ;-)

I've been getting mixed results with Hugin but finally I think I nailed
it. My problem is always the same: how can I keep the verticals in a
panorama? IOW, how can I avoid the panorama to look like a big wavy
line?

Yes, I know about the vertical/horizontal-line control points ("intra"
points) ;-) But it seems ineffective when the number of classic control
points ("inter" points) is comparatively large. In my case, I typically
use 20 "inter" control points and 5 "intra" control points per image. If
I use only 5 inter points and 5 intra points the result is straighter
but the fit is poor.

One quick hack I found is to simply duplicate the intra control points
many times (editing the .PTO file). This nearly solved the problem:
verticals are now much better, the panorama is not as wavy and at the
same time the fit is good.

This brings two questions:

- do we have to use both H and V intra control points to keep the
panorama straight (from a theoretical point of view)? Or can we afford
to use only one type? In my panorama no horizontal feature can be used;
this may lead to the ineffectiveness of the intra control points.

- would it be useful to add some weighting in the solver? Duplicating
points can work but when you have 5000 points it gets a bit slow.
Besides, it's not very elegant... I don't know which method is used in
Hugin (or panotools) but I know some linear and non-linear fitting
techniques allow that.

Thanks for your help,

Damien

-- 
  _    Damien 'Takahara' Douxchamps, PhD
 ('-   Post-doctoral investigator
 //\   Image Processing Group, NAIST
 V_/_  http://damien.douxchamps.net/