Functions for the GIMP plugin "mathmap" used to transform
equirectangular panoramas (typically generated by hugin).

In all cases, the input image is assumed to be a standard
equirectangular image with aspect ratio 2:1.

References:
GIMP: http://www.gimp.org/
Mathmap: http://www.complang.tuwien.ac.at/schani/mathmap/
Hugin: http://hugin.sourceforge.net/

Composite functions:
erect2plane.mmc             General-purpose transform from
                            equirectangular to plane
tiles2plane
Functions:
erect_rot.mm		    Rotates the viewsphere in pitch, roll and yaw.
erect_tra.mm		    Translates the viewsphere a distance d forwards
erect_cyl_tra.mm            Translates the viewcylinder a distance d forwards
erect_crop.mm               Crops the image; use last in composer.
erect_graticule.mm          Superimposes a graticule; use first in composer.
erect_transverse.mm         Rotates viewsphere to put poles on equator
hplane_erect.mm             Transforms a horizontal plane to equirectangular
tiles.mm                    Generates tiled plane
transverse_erect.mm         Inverse of erect_transverse.mm

Typical workflow:

1. Generate equirectangular panorama using hugin.  

2. Load equirectangular panorama  into GIMP

3. Apply erect_transverse; edit nadir (eg to remove tripod) and
   possibly zenith; apply transverse_erect to recreate equirectangular
   panorama.

4. Use one of the composite functions to produce projected image.
   The following user values are in some or all the composite functions

   pitch Pitch of viewsphere
   roll  roll of viewsphere
   yaw   yaw of viewsphere
   fov   field of view (degrees)
   vfov  vertical field of view (degrees)
   hfov  horizontal field of view (degrees)
   d     distance the sphere or cylinder is translated.

The composite functions were prepared in mathmap composer. Composer
can also be used to prepend erect_graticule to give lines of latitude
and longditude and to append erect_crop to do some cropping and
composition at this stage.
   
   P.J Gawthrop September 2008,March 2009, May 2009.