[ptx] hmmm... are there any in-depth explanations of the hugin optimizations?

[Hal V Engel]

On Friday 22 April 2005 11:33 pm, Rob Park wrote:
> So I'm working on updating my tutorial... I went out and took a quick
> panorama of a local park... but I'd been having a hell of a time
> getting it to stitch right...
>
> I couldn't figure out what the problem was. There were horrible stitch
> lines, buildings split in half, etc. My first instinct was that
> autopano was generating bad control points but I looked them over
> meticulously and they all seemed to be exactly correct in the
> images... then I played with different optimisations, and the images
> just would not line up at all... until I did the "optimise for barrell
> distortion", suddenly everything is lining up nicely. I've never used
> this one optimization before, I'm not sure what barell distortion is
> (though this is the second panorama I've made with my new camera, so
> perhaps this camera has more barell distortion than my last one did?).

Barell distorsion refers to the curvature that all lenses impart to the image.  
In most cases this curvature causes straight lines to bow outward and if this 
is bad enough it will look sort of like a barell thus the name.  If the lines 
bow inward then it is called pin cushion distorsion.  But this is really the 
same thing only going the other direction.

I have found that it is usefull to calibrate my lenses so that I have more 
exact numbers to use when optimizing.  There are a number of web sites that 
have directions on how to do this.  But it basically involves shooting a pano 
of something with lots of vertical and horizontal lines (hint think steel and 
glass office buildings) with large overlaps between the images (>50%).  For 
best results you should be shooting from a tripod with a well setup pano 
head. Then you set your control points and make sure these are all good ones 
and then optimize for everything.  When you go to the lens tab the results 
are some fairly good numbers for your lens.  You can then save this for use 
in other projects.  Also if you are using a zoom lens you will need to do 
this a various focal length settings as this can and often does change 
considerably at different focal length settings.  Also zoom lenses tend to 
have significantly more barell distortion than do prime lenses.  F stop does 
not affect lenses distorsion.  

>
> So is there an in-depth explanation of the various hugin optimisations
> available? At the very least I'd like to understand them more, and I'd
> like to link to it from my tutorial when it's done.
>
> Thanks ;)