Materials incorrect in complicated polyhedral model
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tetrahedra only model.skpThe attached is part of a larger model that I've been working on. It shows ten tetrahedra (triangular pyramids) arranged symmetrically. The tetrahedra are in two colors, each as a separate layer. When both layers are showing, on the inner triangles, sketchup bounces back and forth between the two colors, creating a bit of a disco ball effect. I would appreciate it if someone more expert than myself could help me figure out whether it might be possible to fix this problem and make the layers intersect correctly.
It seems possible that this is some kind of round off error and maybe there's a way to make my model more precise. It also seems possible that this is too far from what sketchup is designed to do, that the planes are just too close, and I should work around by either not showing the two layers moving together in my final animation or by looking for different software.
BTW, I created these by first making a dodecahedron (using instructions from one of Bonnie Roskes's Geometricks books). I made cubes inside the dodecahedron, and then tetrahedra inside the cubes (the two different colors of tetrahedra are the two different tetrahedra that fit in one cube). The complete model also has an icosahedron and five octahedra, all with the same radius, and it shows how the various layers look together. I've gotten positive responses to the first draft of the video, and I am working to make it better.
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This is called "Z-flighting".
It occurs in many 3d apps when you have faces that are coincident or almost coplanar.
The graphics engine is unable to make a decision about which face takes precedence consistently. So in one camera angle some purple faces are displayed and at another angle these will be magenta, sometimes it combines the two as a moiré pattern of the two colors !So if you have any objects like groups of components aligned in such a way that there are coplanar faces then you will get this happening. Images don't Z-flight with faces BUT they have to be flat. Cutting components also won't do this but again it only applies to the one face onto which the instance is glued, and won't help you in this your case...
If you can suitably construe your object/layer hidden/visibility states in different scenes [frames] in your animation then you should never get this happening.
Why do you ever want to have the two objects occupying the exact space in the world?
If you are hoping to cross-fade from one color to another you'll have to make some intermediate colored versions and/or post-process the animated frames to blend them ?Another way to avoid Z-fighting is to make one object slightly smaller that the other, that way one will always dominate and display over the other. Scale about the center [+ctrl]. The amount of offset difference in two faces' planes that is needed to avoid Z-fighting depends on many variables - their distance from the camera/angle, screen resolution, perhaps even your graphics-card and/or its settings... You'll need to experiment to see what works in your case...
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Thank you for your reply. It's nice to know that this problem has a name.
I just realized that my problem is actually mathematical not with sketchup -- you are right, I am trying to have two planes occupy the same space! No wonder sketchup can't decide.
I started making this model because I had trouble visualizing it myself, and then what comes up with sketchup is so close to looking like something that "should" be regular that I thought I knew what it was supposed to look like -- but five wedges arranged around a point cannot alternate between two colors. Those wedges are both colors....
So I think what I will do is change the coloring to two lighter colors and then explode the model and paint the faces where they intersect a darker color.
In hindsight, the issue now seems obvious, sigh..... but I appreciate that you helped me get the answer, even if I didn't really ask the right question.... very interesting....
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