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Geometric error calculation

Started by Hiyar Feb 27, 2009 at 4:46 AM 3 replies 1k views

Original Post

Feb 27, 2009 at 4:46 AM

Hi, Is it possible to use geomipmap geometric error calculation for a quadtree based terrain? As far as I know standard geomipmapping uses fixed size terrain patches. I'm using quadtree. The root node covers the entire terrain, then it is split until the highest res reached. Up until now I have used simple distance based creteria for LOD. But that doesn't consider the roughness of the terrain. So, I need to change this.

Hiyar

Author

Hiyar

Feb 28, 2009 at 8:09 AM

No respose yet?

As you might know, the error calculation for same-size-patch based terrain, generally doesn't work for quadtree based terrain. Because the error is local to each patch. However I can add the maximum error of the children nodes to the local error as described in the paper "Rendering Very Large, Very Detailed Terrains"
I have already implemented that idea for geometric error calculation, but I'm getting real crap results
Click
(I have removed edge stitching)

Triangles in rough areas are too dense and in some areas I never get the highest resolution even when the camera is on the ground.

Any idea what is wrong?

Dragon_Strike

Feb 28, 2009 at 11:31 AM

if u posted some code of of u calculate the geometric error and how u choose the different levels to render we might be able to help u...

do u transform the geometric error to screen space error when choosing mesh level/density?

Hiyar

Author

Hiyar

Feb 28, 2009 at 2:25 PM

How do I project it to screen space?
I'm using this formula:

C = screenHeight / (2 * tau * |tan(FoV/2)|)

tau is error threshold.

then multiply C with node error.

Node error is the maximum error of the four children + error of the actual node.

Dragon_Strike

Feb 28, 2009 at 2:49 PM

Quote:
Original post by Hiyar
How do I project it to screen space?
I'm using this formula:

C = screenHeight / (2 * tau * |tan(FoV/2)|)

tau is error threshold.

then multiply C with node error.

Node error is the maximum error of the four children + error of the actual node.

seems right

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