topic Re: Tetrahedron in Modeling

Tetrahedron

Anonymous — Mon, 19 May 2008 20:38:13 GMT

Apparently a tetrahedron can be cut from a cube by cutting the six edges of the tetrahedron along the diagonals of each of the faces of the cube.
This would mean cutting through the section - can this be done with the marquee tool ? Or is there another way ?
Any advice would be appreciated.
Thanks
Rob Warren

Re: Tetrahedron

Anonymous — Mon, 19 May 2008 21:16:37 GMT

I don't think this can be done with the marquee tool.
You could use SEO with an object that can be rotated
about three axes operating on a AC tool element like
a slab or a wall. The easiest way would be to use
the "Pyramid" object in "Basic Shapes" unless there
is a reason why an object would not be suitable.
Peter Devlin

Re: Tetrahedron

Anonymous — Mon, 19 May 2008 21:33:42 GMT

Thanks but what does SEO mean ?
Rob

Re: Tetrahedron

Eduardo Rolon — Mon, 19 May 2008 21:54:20 GMT

Solid Element Operations

Re: Tetrahedron

Anonymous — Mon, 19 May 2008 21:54:50 GMT

SEO means Solid Element Operations. It was a feature introduced
in AC 8.0 and exists in all subsequent versions. If you are working
in AC 8 or above look it up in the help files. If not, then knowing
what it is won't help.
Please add your AC version and platform in your signature.
Peter Devlin

Re: Tetrahedron

Anonymous — Mon, 19 May 2008 22:04:16 GMT

Thanks,
I'll look it up.
My AC version is 11 Build 1210 on PC
Rgds
Rob

Re: Tetrahedron

Ralph Wessel — Tue, 20 May 2008 12:22:03 GMT

Rob wrote:
Apparently a tetrahedron can be cut from a cube by cutting the six edges of the tetrahedron along the diagonals of each of the faces of the cube.
This would mean cutting through the section - can this be done with the marquee tool ? Or is there another way ?
Any advice would be appreciated.

I think the 'Pyramid' shape Peter recommended is likely to quickly and easily solve the problem. However, if you need to form shapes by cutting, take a look at OBJECTiVE, which includes tools to quickly and easily rotate and cut objects in 3D to the shape and orientation you need. I've attached a series of images showing a cube cut down to a tetrahedron. These operations can be done in plan or section, but in this case I stayed with the plan view:

1. Select a basic rectilinear shape and set the bounding size to a 1m cubed.
2. Use the 3D rotate to swivel it around by 90 degrees about the X axis
3. Make the first two offcuts using the Split tool
4. Rotate by 90 degrees on the Y axis
5. Make the last two offcuts
6. The finished result

The end product looks right in 3D and 2D (unlike SEOs), you get snap points on all the vertices, and you can continue to rotate/split the object as required.

You can find out more about OBJECTiVE at:http://www.encina.co.uk/objective.html