[ptx] new tutorial on TCA correction

[Pablo d'Angelo]

Bruno Postle wrote:
> On Wed 15-Mar-2006 at 23:01 +0000, Bruno Postle wrote:
> 
>> On Wed 15-Mar-2006 at 08:52 +0100, Pablo d'Angelo wrote:
>> >
>> > Please take a look at my tutorial on estimation of the TCA correction
>> > coefficients at:
>> >
>> >  http://hugin.sourceforge.net/tutorials/tca/en.shtml
> 
> My mistake, the output is fine, the maths in the tutorial and the
> javascript calculator give good results.

Thanks for the calculator. I have moved it a bit to the top, so that
people without octave can just key in their coefficients, without having to
read all the stuff about the diagrams and octave.

> I found that optimising just c and fov for the red and blue channels
> gave the best output for me.

Yes, especially the a coefficient is hard to optimize since it only really
affects the image corners, where less control points are placed.

> A couple of points:
> 
> Hugin CVS has a bug that makes it difficult to change the input
> projection (I eventually managed to set it to equirectangular by
> selecting every other projection in turn).

Hmm, strange. I haven't experienced this problem (wx 2.6.0).

> The tutorial says to run this octave command:
> 
>  octave:2> display_tca('pano_tutorial.pto');
> 
> ..the correct command seems to be:
> 
>  octave:2> show_tca('pano_tutorial.pto');

Corrected.

> Though I can't see much difference between the fulla output when using
> PTOptimizer and when using the octave script - They seem to be as good
> as each other to me.

I had some problems with the PTOptimizer approach. Maybe the peleng fisheye
shows a quite strange distortion and it tends to be a bit unsharp at the
borders.

Anyway, great that both approaches work for you!

> In my tests, the red and blue channels were both scaled down leaving an
> ugly green border around the photo.  Can the calculation for the fulla
> parameters be adjusted to scale everything so the smallest channel fits
> the image width?

Yes, this is quite annoying, and I'll take a look at this.

ciao
  Pablo