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 Post subject: Projective Grid Mapping
PostPosted: Sun, 11-01-15, 13:42 GMT 
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Joined: Tue, 04-09-07, 2:32 GMT
Posts: 438
Location: South Korea
I recently came across this nice, simple method of generating planetary terrain geometry that has LOD (level of detail) for "free":

Projective Grid Mapping (PGM) for Planetary Terrain (University of Nevada, Reno)

For any LOD scheme, terrain closer to the observer (eye) will render more polygons than terrain further away, since far-away polygons are not as well-resolved by the eye and thus their density can be reduced to save CPU and GPU time.
What PGM recognizes is, that this simply means that we can project a uniform grid into perspective space. Far-away terrain stretches out the edges of the grid in perspective space such that the polygon density is automatically lower for far-away terrain:
pgm.jpg [ 121.76 KiB | Viewed 1911 times ]

This transformation is easy to do on the GPU (it does require that the vertex processor can read textures), and does not require any fancy data structures such as quadtrees, morphing between different levels of detail, etc.

With this technique, planet surfaces can really have bumpy geometry and render realistically (and quickly) even at high zoom levels.

Perhaps something to consider for celestia.Sci?

PostPosted: Sun, 11-01-15, 15:12 GMT 
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Joined: Thu, 25-10-07, 15:20 GMT
Posts: 992
Location: NE PA, USA
This looks like something that I've been wanting to do for the longest time.

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