Geospatial indexing should work with spherical surfaces

Geospatial indexing, and querying those data assumes that a surface is Cartesian surface (flat). This is not the case with the Earth. Treating geographical coordinates as Cartesian coordinates, leads to obvious errors.

I believe $center and $box queries could possibly be "fixed" by most people by upcoming search within polygon SERVER-772, but obviously this won't fix $near results errors.

It is very desired that there is some kind of specifying that geospatial index should work with sphere, not flat surface.

Maybe a way to do it from user's point of view would be:

db.places.create_index(

)

Specifying radius of sphere this way would make sense for people who want to use different units than kilometers, or map things on different surfaces (Mars, anyone?).