Re: OT: Map projections

mvillanu@xxxxxxxxx wrote in news:1152515099.665016.130170
@m79g2000cwm.googlegroups.com:

Forgive this OT but I figure this place is as good as any to ask....

I friend of mine sent me a little program that generates randomized
fractal maps of planets. (Don't ask...I'm a geek...nuff said). The
program allows me to choose what type of map projection I want
(mercator, sinusoidal, etc....)

My question:

I want to take these pictures and map them onto a 3d sphere, in this
case it's a straight UV map onto a NURBS sphere, and to keep things
simple, a cylindrical mapping onto the sphere (though I'm willing to
mess with the UV also).

Question #1
Which projection lends itself most easily for this (mercator, peters,
etc...) so that it's the most aesthetically pleasing/natural looking to
the eye?

Question #2
Perhaps someone knows of a Map projection + texture mapping
configuration that works best?

Question #3
Someone else know of a terrain generator that generates
"sphere-mapping" friendly pics?

I've quickly learned that it's one thing to wrap a sphere using pics
from a real planet. It's another thing to generate realistic looking
planets from fractal generated terrain.


One question that leaps to mind is this: Is the terrain originally
generated in spherical coordinates, then projected onto the map? It
seems likely that this is the case, given that you have a choice of
projections. If the original generation is in spherical form, then
projected, the obvious question is: can you sneak inside the program to
get that data? If so, then it seems like your job is done, right?

If the only info you can get is the projected data, then you would need
to back-project to get onto the sphere (an excellent source for the
common projection equations and their inverses is USGS Professional Paper
1395, Map Projections: A Working Manual, which, alas, is out of print,
but should be available through a library (via interlibrary loan, if
nothing else)). Anyhow, if this is the case (all you can get are the
projected boundaries and such), then choose a projection that does not
have singularities at the poles (e.g. NOT Mercator, orthographic, or
stereographic): sinusoidal, ellipsoidal, Molleweide are a few such.

Best of luck.

--

Jim
"Value nothing but truth, compassion, and love"

.

Relevant Pages

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