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Physics offset

Sharie Criss

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I've created a VERY simple mesh from a deformed plane...


This is used in the corner of a skybox to give a little terrain hill. The model is sized correctly in blender and I only have to make very minor adjustments when I rez it.

No matter what I do, the physics seems off - I hover over the mesh by about .7m. In a few small places, it seems fine:


but the vast majority is way off:


I've taken most of the defaults when uploading the model, selecting the High LOD for the physics model as this is a pretty low-poly mesh. I've tried selecting the model DAE file for the physics model too, no change.

I'm using the latest Blender, and have tried both the 4..5.1 firestorm and latest LL SL Viewer for uploading.



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Bingo. That did it. Thanks! It is unfortunate that the cost went from 3 to 10. That's quite an insane LI calculation on LL's part. I could probably make a similar hill from a bunch of prims that have 100 times the vertexes for half the LI. Bleh. The LI for mesh is still way too high. A simple mesh model like this should not have that kind of LI.

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Hi :)

A couple of tips for Creating a mesh terrain with accurate physics and a low LI .

I guesstimated the size of your terrain to be around 18 x 18 x 4 meters and when uploading and setting the Physics Shape Type to Prim the original terrain had a LI of 10 and the Optimized version an LI of 3.

1) Remove all unnecessary vertices :

Minimize vertices.png


2)  In Step 1 of the  Physics tab in the  mesh uploader use the High LOD mesh for Physics shape.

Very important DO NOT ANALYZE in Step 2 . This will leave it as a triangle based physics shape.

When you have large triangles like in this terrain not Analyzing the Physics shape will give the lowest Physics count in the LI calculation.


3) Rez the terrain and set the Physics shape Type from the default Convex Hull to Prim.


Edited to add:

Because the Physics cost (3.1) was higher than the Download weight (1.0) in the LI calculation of the optimized mesh it is possible to increase the size of this mesh terrain to 50 x 50 x 10 and still have a LI of 3 (Download 3.4,  Physics 1.2, Server 0.5)

Note when using the Not Analyzed Physics shape the Physics part of the LI calculation will get smaller the largeryou make the mesh .


Edited a second time:

In the above example I had left the terrain mesh as Flat shading in Blender before exporting because I think this gives a better finish to a terrain mesh when rezzed and textured in SL. However I tried uploading a smooth shaded version then the 50 x 50 x 10 meters size terrain (when set to physics type Prim) came in at LI = 1 (Download 1.4, Physics 1.2, Server 0.5).

If you are carefull with how you place the vertices and avoid small triangles sometimes mesh can be used for terrain :)


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Absolutely fantastic advice, I plan on trying this out right away - thank you so much for your very detailed response!!!



My new hill has an LI of 2 with the prim physics type - MUCH more in line with what I would expect :) Thanks! And the easy way of nuking the unneeded verticies, the Decimate modifier. Does most of the grunt work that can be hand tweaked.

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