[ptx] Projections (was Alternative fisheye projections)

[JD Smith]

On Fri, 2006-04-07 at 00:22 +0200, Pablo d'Angelo wrote:
> Peter Gawthrop schrieb:
> > I'd like to play around with other projections.  The idea is to
> > stitch a rectilinear 2x1 and then project it to make it look good.
> > 
> > So far, I have modified sphere-slicer.pl by Bruno Postle to do this
> > for Mercator's projection (using formulae from
> > http://mathworld.wolfram.com/topics/MapProjections.html). The problem
> > is that it is slow. Before I plunge in to other projections, I would
> > like to be sure I am on the right path.
> > 
> > Do you thing perl is the correct approach? Or would modifying nona/hugin be
> > a better approach? I guess the main issues for me are speed and
> > interpolation quality.
> 
> Here is a patch that adds the mercator projection to libpano12.
> just use f4 in the p line use it.
> 
> I have only tried using it with PTmender (should also work with PTStitcher).
> It should also be possible to optimize mercator panos, but I haven't tested
> it yet.
> 
> Support for it from within hugin and nona will follow later.
> 
> Are there any other interesting projections that should be included in
> panotools?

Hi Pablo:

Very nice.  Here's a discussion we had on the PanoTools list about what
projections might be interesting to add:

http://thread.gmane.org/gmane.comp.graphics.panotools/22701/

I was advocating the Lambert cylindrical (or any of the equal-area
cylindricals) as a better alternative for printing than a straight
cylindrical, for panoramas with more than ~100-120deg vertical field of
view, since at latitudes phi=+-90deg, they map to y=+-sec(phi_s) rather
than y=+-infinity.  See:

http://mathworld.wolfram.com/CylindricalEqual-AreaProjection.html

compared to:

http://mathworld.wolfram.com/CylindricalProjection.html

Up to about +-30deg of latitude, Lamberts and the "plain" cylindrical
are very similar.  Above that, the cylindrical starts racing out of
control.  This class of projections would allow full 360x180 printed
panos that might look less strange than a standard cylindrical (as would
Mercator). 

JD