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soconne

Num of Triangles Being Rendered With Geomipmapping

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I have a simple question for those of you that have implemented Geommipmapping terrain. How many triangles do you usually draw per frame using, let''s say a 256x256 heightmap or 512x512 heightmap ? Because currently I have my own terrain system set up to where it generates a ''static'' terrain mesh that is optimized using a form of Roam so i can have less triangles in flat areas and more in mountaneous areas. When i do this, depending on what quality I want, I get between 3,000 - 8,000 triangles for an entire terrain landscape, and this suits my needs just fine. What I''m wondering is whether using Geomipmapping I''ll get less triangles per frame to render or more? Because I''ve downloaded some geomipmapping demos that render an incredible amount of triangles but it runs really really fast.

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It is hard to say, but using the same error metric, it is likely that your method will result in less triangles.

In geomipmapping, the resolution of the of each patch is depends on all the vertexes in the patch and patches will have areas with unnecessary resolution. Assuming that resolution is decided for every vertex in your method, it is more efficient as far as number of triangles is concerned.

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but also keep your target machine in mind. current cards might still be happily smiling if you brute force render a 256x256 heightmap. for the visible part of a 1536x1536 terrain its about 40-60k to avoid too visible popping.

if you have an nvidia you can try it yourself.
terrain

readme has the interesting keys (f, v, home/end and d might be of interest to turn of fog, increase the view distance, adjust the lod and selection method)

just found a version for nvidia/ati (cards with fragment programm support only). stats via 'm' on console. obviously less geometry closer to the ground (occlusion culling).
here

[edited by - Trienco on May 8, 2004 1:59:38 AM]

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I just finished writing a terrain simulation using a modification of Rottger''s geomipmapping technique. I''m getting about 1000-1500 triangles for a relatively detailed 512x512 terrain.

The choice of static/dynamic depends quite a bit on just how jagged the terrain is; if your terrain has a lot of detail, then a static mipmapping method will either lose a lot of detail or generate a lot of triangles.

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Hey zaambu, you are getting 1000-1500 triangles ''per frame'' using geomipmapping or are you using a static mesh ?

If you are using geomipmapping, got any pics :-) ?

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On a 32768 x 32768 heightfield, I typically render about 300,000 triangles out to the visible end at around 15 kilometers. This is aiming at Radeon 9700 and higher cards.

On a GeForce 2 MX, on an "earth sized" fractally/artist-blend generated heighfield, we draw about 8,000 triangles per frame, out to a visible end of about 10 kilometers (i e, much lower resolution
:-)

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quote:

Because currently I have my own terrain system set up to where it generates a ''static'' terrain mesh that is optimized using a form of Roam so i can have less triangles in flat areas and more in mountaneous areas.



Why not use your roam algorithm to generate your geomipmap levels? You could just adjust your error metric for distance. This way you wouldn''t have to rebuild your vertex and index buffers every frame, but you would still get the optimization from your roam algorithm. What do you think?

Jason Z

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