Question about prim equivalents/land impact

[Jun Yiwama]

Can someone explain me all the aspects of prim equivalents/land impact? like, how many vertices/faces make a single prim equivalent and how to make sure your meshes would remain the same polycount as they were in the program you've modelled them? (for me it's blender) because for instance, I've uploaded a model that had 6k vertices in it and once i've exported it using collada and imported it into SL it was 12k polygons and 60 prims worth of land impact. From what i understand the problem lays in collada as it turns every quad face into two triangular faces i.e makking the polycount twice it's size, but i still don't get why its 60 prims. 

[Drongle McMahon]

Calculating the prim equivalent weight (now called land Impact) is rather complicated. You can find all the details by starting with this wiki entry. A few quick points that may help...

1. Three weights are calculated, download weight, physics weight and server weight. The highest of these is used.

2. Download weight, at a particular size, is only very roughly related to the triangle count. More accurately, it depends on the size of the compressed download data in the internal SL format. This depends not only on triangle and vertex counts, but also on amounts of material boundaries, UV seams and sharp edges. It also depends on the compressibility of the data. Collada can use polygons (up to quads if you use Blender), but they are converted to triangles by the uploader.

3. The vertex count you see in the uploader will often be more than that you see in Blender because extra vertex entries in the vertex list are required when the same position appears with diffrerent normals or different UV coordinates.

4. The download weight increases with size. The value in the uploader refers to the dimensions of the model and the scale factor in the uploader. If you stretch the uploaded object after rezzing it, it will increase the PE (and if you shrink oit it will decrease the PE).

5. The physics weight depends on whether you have supplied a physics shape and whether you have decomposed (Analyzed) it or not. If noe is supplied, the physics shape is the default convex hull. If one is suppled and decomposed, it is a collection of convex hulls. If it is not decomposed, it is a triangle-based shape. the weight of triangle based shapes increases with decreasing size (!). The convex hull weights are independent of size. Small traingles can cause very high physics weights in triangle-based shapes.

6. The server weight will only be bigger than the other weights for very simple meshes. It is calculated at the level of the linkset. It is a minimum of 0.5 per mesh (Blender object) in an uploaded linkset. It increases to 1.0 per mesh if any linked prim contains a script. If you have only one mesh with server weight 0.5, and that is the highest of the weights, the PE will be rounded up to 1.