Same triangle count but double vert count during upload?

[Sybil Hallison]

Hello, I am working on a mesh building and I am currently trying to reduce my poly count, before messing with LOD and physics .

I was looking for building components in my design, that increase by much my poly count. After a lot of trial and error, I found a "guilty" spotlight rack which was mirrored along the whole building (4 racks total). Even if it had low vert count, it had 50LI. I removed the mirror modifier and exported one single rack which then had around 3LI. Because 50LI is way more than the 3x4=12LI , I supposed there was something wrong with the physics calculation so I moved on and tried to reduce even more the poly count of this rack.

My original model had 358 verts and 640 tris, after some modification I ended up with 288 verts and 516 tris. When I tried to upload the new model to SL I noticed that the LI didn't change by much. I also noticed that even though the tris count was identical on blender and on uploader the vert count shown on uploader is 785 while blender shows 288 verts.

Is this normal? Am I doing something wrong or am I missing something obvious here?

I also forgot to mention that I was using both Avastar and the default export for exporting the dae file

Edited September 20, 2018 by Sybil Hallison

[Kyrah Abattoir]

Hard edges and UV seams will create extra vertices, it's normal

[Sybil Hallison]

Thank you for your answer Kyrah, good to know...
Does that vert increase play any part in the LI calculation? Or should I ignore it and start messing with physics now for more optimized results?

[Pamela Galli]

I am wondering how you wind up with so many more tris than verts.

in any case, hard to comment without some more screenshots 

[Kyrah Abattoir]

Show us the wireframe?

[Macrocosm Draegonne]

I had noticed a few more sometimes but double seems excessive, too many hard edges and seams?

[ChinRey]

10 hours ago, Macrocosm Draegonne said:

I had noticed a few more sometimes but double seems excessive, too many hard edges and seams?

The uploader's vertice splitting is not a big problem. The normals data makes up the bulk of the info a vertice has to hold and splitting that data across several vertices rather than heaping it all onto a single one doesn't really make that much difference. It's not ideal but it's not even on the top hundred list of SL mesh flaws.

There is of course a limit to how many vertices a single mesh can have in SL but it's very high and a mesh that us anywhere near that limit isn't suitable for a dynamic 3D environment anyway.

[Beq Janus]

On 9/20/2018 at 7:31 PM, Kyrah Abattoir said:

Hard edges and UV seams will create extra vertices, it's normal

Normal is exactly the right word.

Mesh in SL has vertex normals only (no face normals) in order to create a hard edge you get an edge split occurring, one vertex carrying the normal to the first plane, the other carrying the normal to the other. In a simple cube, you get a 3-way split. making your 8 vert cube a 24 vert mesh.

The following shows two simple cubes in Blender. The second one has had an edge split modifier applied to it to create the effect that SL upload will create. A vertex can have just one normal and thus you end up with each vertex in triplicate. Sometimes you can get away with it, the cube on the left here will look perfectly fine a lot of the time, but placed in the "right" lighting" especially if you are using materials on it, the smoothing will be very apparent.

 

There is another source of doubling that can occur too, every material that you have on your object is defined as a separate "inner" mesh within the mesh unit itself. In doing this vertices can be duplicated. On the plus side, if a hard edge has already split it then no further duplication will occur.

On 9/21/2018 at 3:46 PM, Sybil Hallison said:

Thank you for your answer Kyrah, good to know...
Does that vert increase play any part in the LI calculation? Or should I ignore it and start messing with physics now for more optimized results?

The vert count has an indirect impact on the LI in the sense that the streaming cost of the mesh is based on the overall size of the mesh data once it has been compressed. but as @ChinRey says the return on your efforts there are tiny, and unless you can do away with the hard edges and remain happy with the shading that is not normally a place to hunt optimisations unless you are desperate or obsessive. 

[Kyrah Abattoir]

The only place i can think of edge splits raising dramatically is if you where to make a checkerboard-type model.

[ChinRey]

1 hour ago, Kyrah Abattoir said:

The only place i can think of edge splits raising dramatically is if you where to make a checkerboard-type model.

You know, I can actually imagine some SL mesh makers creating a checkerboard with separate triangles and vertices for each tile.

Kind'a scary.

[Kyrah Abattoir]

It's not so bad if all you're making there is a checkerboard.