# brillouin zone modelling problems: bissecting plane, plane intersection

Hi,

I’m trying to model the brillouin zone of an FCC crystal, which is a truncated octahedron:

I want to visualize the octahedron inside the FCC structure made up of spheres.

I was hoping to find an easy way to place the planes between the spheres and then model their intersection as lines/cylinders.

Actually, while writing this post, I think I found a “manual solution” to my problem using the following 2 tricks:
http://blenderartists.org/forum/archive/index.php/t-144358.html

1)Basically, I measure the distance between 2 spheres to get a line object between them.
2)Then I select the line and snap the cursor to its center (shift+S)
3)Then go to “User preferences” window, in the “Edit methods” tab, enable the “Align to view” button.
4)Select local axis system
5)Align view to selected
7)Rotate plane locally as needed (r-x-x, r-y-y or r-z-z with +/-90)

Now in principle I just need to add flat cubes instead of planes to be able to use booleans correctly for the intersection.

But if you know of any better way to get a line from 2 intersecting planes, faster ways to do it or any scripts which can help with modelling such things, please let me know.

In 2.5x, the ‘Regular solids’ add-on will give you a truncated octahedron.

Now in principle I just need to add flat cubes instead of planes to be able to use booleans correctly for the intersection.

It’s best to avoid booleans for this sort of low-level modelling. (They do have good uses, but not this.)

But if you know of any better way to get a line from 2 intersecting planes, faster ways to do it or any scripts which can help with modelling such things, please let me know.

In 2.49 you can align the view and then use the knife with vertex snapping and view X or Y constrained motion; there’s also a geometry tools script (though I’ve not used it). I know of no effective way of doing anything like this in 2.5x.

Best wishes,
Matthew

Thanks, this is great.
(actually, I made a mistake: What I need is a rhombic dodecahedron. The truncated octahedron is for the reciprocal lattice. (brillouin!=wigner-seitz))

For the plane intersections, it’s probably best to write a script, but I don’t want to do that right now.

I used the add-on to add a “rhombic dodecahedron”, but am now trying to align it correctly.
Basically, each face should point to one of the closest spheres and be on the middle of each sphere-sphere segment.

I tried the tracking function (ctrl+T) to align one face, but then I can’t rotate the object anymore.

I’m attaching my current blend file.

Any ideas of how to do this easily?

### Attachments

brillouin21.blend (976 KB)