Vertex group problems

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Vertex group problems

Post  cgen2 on Sun Mar 29, 2009 7:59 pm

Blender is giving me grief. My problem seems real basic so I can't be the first to hit it. Any help gratefully received.

I'm using Blender 2.48a on an iMac running Mac OS 10.5.6.

For example, I have a reasonably simple model (a wing) with one texture on the top and one on the bottom surface. I separate the vertices (by selecting faces) into two groups and assign two materials. I try to create two vertex groups matching the materials but Blender always selects another face from the wrong group. Sometimes Blender selects another two or three faces. Consequently I can't create the requisite two vertex groups. Sometimes the problem has a different symptom with the wrong texture selected on a material.

Blender itself renders the object in the 3D view OK with the textures on the right faces.

In my example I have fiddled about until I have avoided the problem but when I convert to triangles for SIO2 one of the faces appears in the wrong group. This is a recurring problem and I have not been able to devise a workaround. Please help before I do something silly ...

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Re: Vertex group problems

Post  Jawdy on Mon Mar 30, 2009 8:40 am

Is the wing too complex to have as once full object with one texture? Or does it not "fold" out well to the UV's for drawing?

I'm not too sure what you're trying to achieve in Blender as I've never done this myself, but some stuff with Blender->SIO2 to check: Have you checked all your normals? Have you "center new" all your objects?
Not sure if they would make a difference, but trying to help in some small way, if I can.
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Re: Vertex group problems

Post  cgen2 on Tue Mar 31, 2009 1:27 am

Jawdy - not too complex but we have two different textures for the top and bottom surfaces of the wing. Blender's "Project from view" does a good job of unfolding to UV. Blender handles simple cases Ok, eg single material or texture. If I select a set of vertices and assign it to a group then use CNTL-I to select the other set and assign it to another group, I expect to have two non-overlapping sets. This separation is necessary for SIO2 to render properly. Blender itself doesn't seem to rely on vertex groups or materials to render, at least in the 3D View. Blender's 3D view is invariably OK. The problem only becomes evident when using SIO2. The SIO2 response follows:

Take a look at this video tutorial:

http://www.youtube.com/watch?v=HYjnP3jQIiw&fmt=18

http://www.youtube.com/watch?v=OI499KsFmF8&fmt=18

Also work with the vertex group on a triangle basis... I had similar problems as you what I did was to simply separate certain triangles of the mesh before the SIO2 optimization phase... Blender and SIO2 are handling vertices / triangles completely differently so... You need to be aware of the work around Wink

Hope this helps,

Cheers,

Back to me. I find normals are very useful when grouping faces and hence vertices. The point about working with triangles is well made. The disadvantage though, is that it does add to the clutter increasing the number of faces I have to select - fewer faces are easier than more faces. (I find faces are much easier to work with when separating materials). I'll try working with triangles but this way of working does not seem very satisfactory. I suspect that this is a bug in Blender that goes unnoticed in Blender. What do others do? Are there other work arounds?

PS. I note that simple shapes can't necessarily be separated into two sets of non-overlapping groups of vertices, e.g. minimal cylinder.


this often doesn't I often have problems with this.
I am now fairly skilled with Blender in some areas. I try to protect the art department (my son) from the vagaries of software.

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