What I did:
I constructed an ellipsis segment by adding a circle (128 vertices), deformed it as an ellipsis and deleted ~75% of the vertices. A circle was “parented” to that segment. Then I set “DupliVerts” and “Rot” on in the Animation Settings.
What I expected:
All circles should be displayed perpendicular to the tangent.
What the problem is:
The circle orientation varies in an unexpected manner.
What I request:
Is there a problem in my modeling, with my configuration of the DupliVerts or does Blender behave unsufficiently?
Since the elipse is constructed of vertices and edges, there are only vertex normals. Vertex normals project from the object center through the vertex. Hence all of your circles are aligned with the center of the object.
What you want to use instead are face normals (ie: normals.) To turn your elipse into an elipse with faces, extrude the elipse, however slightly. Then use dupli-faces instead of dupli-verts.
Thanks for all your answers. “Orinoco” gave me the insight. I should have asked “What are vertex normals?” If I look to my own (!) screenshot again, it is now obvious that the normals are calculated with the origin of the object. I thought the edges have any effect. If I rethink this, this can’t be - what would happen if there is none or more than one. So once again I was taken in a wrong assumption. Are vertex normals documented somewhere?
Not in any obvious places. After a bit of searching, I found this
In Blender right now, convertBlenderScene.c has a normal weighting feature in normalenrender(),
which seems to only kick in when AutoSmooth is on. (Otherwise it uses the averaging method that
seems to be somewhere else in the code.) That code uses the cos*1 of the negative of the dot
product. So, an angle of 0° has a weight of zero, and angle of 90° has a weight of , and an angle
of 180° has a weigh of 2. I’m guessing the idea is that the normal between the edges that make
up a wider span of the intersection should have a greater weight. It seems nice, but in my
experiences actually made things slightly worse
but it has no date and does not refer to any Blender version number (typical!) so I’ve no way of knowing how up to date this is, or even whether it is accurate. The MeshTools 1 panel has a Vertex Normals button on it, if selected, it will show the vertex normals. I suspect that my earlier observation about vertex normals only applies to circles and elipses.
