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ROMSEY Homewood

MESH: Why does a mesh model increase its Li when i reduce it's size in world?

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Hi Guys & Gals

as the subject says "MESH: Why does a mesh model increase its Li when i reduce it's size in world?"

 

And how is it when i make a similar model, same size, LESS faces, it uploads as 3Li?

 

I am a bit confused!!! :matte-motes-dont-cry:

 

Thanks in advance for your wise words.

 

ROMSEY Homewood

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Optimizing mesh with regard to SL's Land Impact value is an art.  It's hard to say without seeing precisely what you've modeled why your LI is what is or if it could be better.  There's quite a bit that goes into the whole calculation, inluding different models to be used for the vaious LOD's.

There are a ton of mesh tutotials out there if you do a Google search which may help you as well as any other input you may receive here.

It's very rewarding to learn how to model mesh. 

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If your model has very thin parts with narrow edges, they will be represented by long, skinny tris.  The thinner you make those parts, the skinnier the triangles get, and the harder the servers work to render them.  Hence the higher L.I.  If you built your physics model from it, you might want to replace thin walls and similar parts with pairs of planes so that you have no edge faces on them at all.

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Increasing LI when you shrink a mesh can only happen if the the physics shape is triangle-based (mesh specified, but "Analyze" button not clicked in the physics tab), you have selected physics shape type "Prim" inworld, and the physics weight is higher than the download weight so that it becomes the LI. As Rolig says, this is because the physics engine collision detection hates small/narrow triangles.

What kind of physics shape is best depends on what your model is. Removing narrow triangles along edges will work to reduce the physics weight for walls etc. Otherwise you can use a hull-based shape (click "Analyse" - this works best if your physics msh is made of non-overlapping simple comvex pieces). Which kind of shape gives the lower physics weight is dependent on the details, including the size. Either way, you can reduce the physics weight by simplifying the physics mesh as far as possible while keeping just enough geometry to get the desired collision behaviour. Using the same mesh(es) as for the visible meshes only produces a good physics shape in rare cases.

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Just to add :

  For most small mesh objects, for example a table, an earring, a pot plant or a postbox etc a simple box will do for physics. And because the physics mesh is always stretched to fit the bounding box of the visual mesh the same box will do for them all. :)

So for all things like that create a cube in your 3D software, export as Collada.dae file and save it as  Cube_Phys.dae to your desktop or where-ever, so that you have it easily available. Then when you are uploading your mesh object you can upload this Cube_Phys.dae file in Step 1 of the Physics tab of the mesh Uploader and in Step 2 you should hit the Analyze button.The Physics weight will now never be more than 0.4 in the LI equation no matter how big or small you resize mesh.

 

The increase in LI you experienced with your Non Analyzed mesh when making it smaller is not a bad thing. As others have already said reducing the size of your mesh is also reducing the size of the triangles used to make up your physics mesh and you are being penalized for that.

It follows that using very big triangles will DECREASE the Physics weight in the LI equation. Which means for large mesh objects like buildings you can take advantage of this by creating your Physics/collision mesh using polygons/tris/planes as large as possible and avoiding all small and thin planes/tris in this mesh. This type of Physics model should NOT be Analyzed in Step 2 of the Physics tab in the uploader. (Remember to set to Physics Shape Type Prim once it has been rezzed inworld).

 

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