Semi-Globe image preparation
Here are some ways manipulate the images digitally in order to produce printed patterns for globemaking:
1. Test: using Flaming Pears Photoshop Plugin Flexify 2
2. Test: using the make_gores.pl Perl script and GIMP
3. Test: using ppmglobe from the netpbm collection
4. TODO: trying ISIS2 from the US Astrogeology Program
Conclusion
Mapping a mercator projection onto a sphere for making globes is done in different ways.
Traditionally gores in a form of orange peels from pole to pole are cut out and glued onto a glass ball.
Also possible seems a so called flower petal pattern where the surface of the planet is cut in two hemispheres along the equator
and the poles make the center of the flower petal. Since the orientation of the
paper grain is defines the way
the paper expands when soaked in water based glue ths approach has serious drawbacks.
A third way is that the globe image is printed on a film which has thermoplastic properties and is stretched on the hemispheres
in the manufacturing process. This is how the most commercial globes are made today.
All the tested algorythms fail to produce the proper results because they all don't take into account that the gores themselves stretch
across the sphere when glued on it.
Seemingly the tested algorythms follow this wrong example with a:
trivial formula for
mapping a mercator projection onto a sphere.
The right projection is illustrated here:
Böhm Wanderkarten
Also the Books “Map Projections - A Reference Manual” by Lev M. Bugayavevskiy and John P. Snyder, 1995
ISBN 0-7484-0304-3 on page 222 and
“Kartographische Netzentwürfe” by Karlheinz Wagner, 1949 (and 1962)
ASIN B0000BP33E
on page 155 feature correct calculations, but it seems no software is available to easily employ the correct formulas.