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Spherical Projection

Topics: Algorithms
Aug 2, 2007 at 2:08 PM
Edited Aug 13, 2007 at 10:47 AM
Is it possible to add spherical projection (as used on TGlobe, Satscape, Amiglobe, STSPlus, Google Earth etc.) to the list of available projections? It would help considerably in certain application scenarios and should help reduce the near-polar distortions of flat-map projections.
Aug 6, 2007 at 6:04 AM
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Aug 7, 2007 at 6:48 AM
A spherical projection? What do you mean by that? (in my mind that doesn't even make sense, because a projection tries to get away from the spherical coordinate system by projecting them onto a 2D plane),

The data that Google Earth uses is in a Mercator projection, which distorts the poles toward infinity, so this gives you huge distortion at the poles, so I'm not following you on that either. Furtermore the Mercator projection is supported by Proj.NET that is used by SharpMap for reprojection.

You say you need low distortion at the poles. Are you looking for one of the polar projection methods?
Aug 8, 2007 at 5:42 AM
I would guess he means a spherical ellipsoid used in the datum...

...on which the projection is based....

The polar-projection doesn't make sense, unless you assume some kind of polar-based projection on the aforementioned spherical ellipsoid, which would be a pragmatic assumption to make.

Not everyone is as versed in these matters, so it is probably wise to cut a bit of slack...
Aug 13, 2007 at 10:47 AM
Apologies for the poor phrasing. I have probably misused the relevant terminology, as indeed my GIS experience is limited. So I will rephrase in layman terms.

The applications & libraries I mentioned have the option of displaying the earth as a true 3D sphere.


They all do this in addition to being able to displaying 2D maps.

The question is whether it is feasible to add this capability to the SharpMap library.
Aug 14, 2007 at 7:36 AM
Common to all these 3D applications is that they use 2D images projected onto a sphere. So yes you can use SharpMap to construct the images. Depending on how you map these images onto the sphere decides what projection you should use. SharpMap has before been successfully used as a server for both Google Earth, Virtual Earth 3D and NASA World Wind viewers.
SharpMap doesn't have any 3D rendering engine, and there are no plans for this in the roadmap. To put it very simple, SharpMap is "just" a tool that reads spatial data and renders it onto raster images.
Of course, I'm sure you would be very welcome to start such a 3D project that builds on top of SharpMap ;-)
Aug 14, 2007 at 9:43 PM
There is a 3D engine in the works, albeit very cursory. However, all the primitives and basic math is there. It's in the v2.0 source tree. Check it out.
Aug 15, 2007 at 8:22 AM
Thank you. I will look into it.