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View Full Version : help! how do i model a "Dodecahedron"


yairmann
03-25-2007, 08:19 PM
in MAYA 8 .

i need to create a Dodecahedron (like soccer ball) but without the hexagon faces,
only 5s

kirigoi
03-26-2007, 11:07 PM
Hmmm... Are you sure you mean a dodecahedron? A soccer ball is a truncated icosahedron. I presume you do as you mention it needs only pentagonal sides (i.e. a regular dodecahedron, as dodecahedron simply means any object with 12 faces).

I'm not sure if there any geometry tricks you could use to make one directly out of primitives (does Maya not allow you to create platonic solids?), but as long as you don't mind entering a few vertex values you can create one fairly quickly. I can't show you in Maya, but the following method should work fine anyway.

First create a 2m polygonal cube centred on the origin. It's vertices should be (1,1,1), (-1,1,1) etc. Slice the faces of this cube as follows:

http://www.skylight3d.com/images/CGTalk/screens/dodeca_01.png


There should be slices on the sides hidden as well, but in the same pattern so that none of the slices meet on the same edge. Pay attention to the axes I have defined as they may be different to the default Maya ones and I will refer to them later.

Now create a single vertex (not a polygon unless there's no other way), with values of (1/a, a, 0) where a is the golden ratio (1+√5)/2 m. This is approximately (61.8cm, 1.618m, 0).

Mirror this on the x-axis and the y-axis so you have 4 points above and below the cube.

Copy these points, rotate them 90 around the y-axis, then the x-axis. You should now have 4 points in front of and behind the cube.

Copy the top 4 points again, and rotate them 90 around the z axis, then the x axis to get points left and right of the cube. These 12 vertices will be used to adjust the cube to the right shape. The points should be in the locations shown below (click to get a high-resolution screenshot). Only half the vertices are highlighted for clarity.

http://www.skylight3d.com/images/CGTalk/screens/dodeca_02_small.png (http://www.skylight3d.com/images/CGTalk/screens/dodeca_02.png)


The points are fairly close to the cuts you made in the cube earlier. All you have to do now is weld each of the points at the end of these cuts to the nearest of the vertices you've created like so (only half shown again):

http://www.skylight3d.com/images/CGTalk/screens/dodeca_03.png


When all twelve vertices are welded you should have a completed dodecahedron (click to expand):

http://www.skylight3d.com/images/CGTalk/screens/dodeca_04_small.png (http://www.skylight3d.com/images/CGTalk/screens/dodeca_04.png)


I hope that makes sense, it's a bit hard to describe the steps. If you want I can make a video tutorial to show it in more detail, but given that I'm not using Maya it may not be very useful when it's the concepts that matter. There's probably a bunch of other ways you could do this too, so let me know if you find a more elegant solution (you could do it by physically scaling the cuts themselves by the golden ratio for example).

Let me know if you have any questions. M

kirigoi
04-28-2007, 05:58 PM
You're welcome, I think ;)

Yairmann only has 3 posts, so I guess he's long gone...

kirigoi
04-28-2007, 06:20 PM
Oops, double post

schiz0
04-29-2007, 06:36 AM
Well his join date is 2004, so i'll assume he's just someone that browses the forums with little to say.

Beanmaster
04-30-2007, 06:03 PM
In Maya there is one ready to go: Create->Polygon Primitives->Platonic Solids opt. then choose Dodecahedron.

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04-30-2007, 06:03 PM
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