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### creating a tetrahedron frame

Posted: **Wed Dec 26, 2012 10:18 am**

by **zappfinger**

Hello,

I am trying to create a tetrahedron frame, consisting of cylinders.

Any ideas?

Richard

Posted: **Wed Dec 26, 2012 1:22 pm**

by **Mr.Yeah**

At least I can tell you how to make tetrahedra.

There's a script named add_mesh_solid.py in scripts\addons. When the add-on is active, you can create a tetrahedron with

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`bpy.ops.mesh.primitive_solid_add(source='4')`

Look at the source code so you understand how to get the right vertices. I think you'll need something like this (taken from add_mesh_solid.py)

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```
s = sqrt(2)/3.0
t = -1/3
u = sqrt(6)/3
v = [(0,0,1),(2*s,0,t),(-s,u,t),(-s,-u,t)]
```

so you can use v as a basis to create cylinders with

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`bpy.ops.mesh.primitive_cylinder_add()`

Article of primitive_cylinder_add() in the Blender API documentation

Posted: **Wed Dec 26, 2012 6:14 pm**

by **zappfinger**

Thanks, I will take a look.

I was trying along another path, having found the code to create a tetrahedron and also some code to create a cylinder between 2 points.

But combining then does not give the correct result:

import math

import bpy

from mathutils import Vector

def doCils():

X1, Y1, Z1 = 0, -1 / math.sqrt(3),0

X2, Y2, Z2 = 0.5, 1 / (2 * math.sqrt(3)), 0

X3, Y3, Z3 = -0.5, 1 / (2 * math.sqrt(3)), 0

X4, Y4, Z4 = 0, 0, math.sqrt(2 / 3)

D1x, D1y, D1z = X2-X1, Y2-Y1, Z2-Z1

doIt(D1x, D1y, D1z)

D2x, D2y, D2z = X3-X2, Y3-Y2, Z3-Z2

doIt(D2x, D2y, D2z)

D3x, D3y, D3z = X4-X3, Y4-Y3, Z4-Z3

doIt(D3x, D3y, D3z)

D4x, D4y, D4z = X4-X1, Y4-Y1, Z4-Z1

doIt(D4x, D4y, D4z)

def doIt(dx,dy,dz):

Vaxis = Vector((dx, dy, dz)).normalized() # versor

Vobj = Vector((0,0,1)) # z axis versor

Vrot = Vobj.cross(Vaxis) # rotation axis: normal to both vecs

angle = math.acos(Vobj.dot(Vaxis)) # angle between Vaxis and Vobj

Cone = bpy.ops.mesh.primitive_cylinder_add(radius=.1)

bpy.ops.transform.rotate(value=(angle,),axis=Vrot) # rotate

doCils()

Posted: **Thu Dec 27, 2012 9:25 am**

by **Mr.Yeah**

I didn't look closely at your code so I don't know why it doesn't work but it's way too complicated. Here's the code I made:

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```
import bpy
from math import sqrt
from mathutils import Vector
def cylinder(a, b, radius=1.0):
depth = (a-b).length
location = a.lerp(b, 0.5)
rotation = Vector((0, 0, 1)).rotation_difference(a-b).to_euler()
bpy.ops.mesh.primitive_cylinder_add(
depth=depth,
location=location,
rotation=rotation,
radius=radius)
def tetrahedron_frame(radius=0.1):
s = sqrt(2)/3
t = -1/3
u = sqrt(6)/3
v = [(0, 0, 1), (2*s, 0, t), (-s, u, t), (-s, -u, t)]
cylinder(Vector(v[0]), Vector(v[1]), radius=radius)
cylinder(Vector(v[0]), Vector(v[2]), radius=radius)
cylinder(Vector(v[0]), Vector(v[3]), radius=radius)
cylinder(Vector(v[1]), Vector(v[2]), radius=radius)
cylinder(Vector(v[2]), Vector(v[3]), radius=radius)
cylinder(Vector(v[3]), Vector(v[1]), radius=radius)
tetrahedron_frame()
```

And next time please use the

Posted: **Thu Dec 27, 2012 9:36 am**

by **zappfinger**

Thanks very much!

Very usefull and definitely more elegant.

Richard

Posted: **Thu Dec 27, 2012 10:28 am**

by **Mr.Yeah**

BTW: You can add an option to scale the frame while creating.

Replace

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```
def tetrahedron_frame(radius=0.1):
s = sqrt(2)/3
t = -1/3
u = sqrt(6)/3
v = [(0, 0, 1), (2*s, 0, t), (-s, u, t), (-s, -u, t)]
```

with

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```
def tetrahedron_frame(radius=0.1, scale=1.0):
s = sqrt(2)/3*scale
t = -1/3*scale
u = sqrt(6)/3*scale
v = [(0, 0, scale), (2*s, 0, t), (-s, u, t), (-s, -u, t)]
```

cu

Mr.Yeah