Hi, I havn’t done much with rotations yet, but for a script I am working on at the moment I need to rotate a mesh (not Object Mesh) to be aligned with another.
The mesh I want to rotate is aligned with the x, y, z -axis, but I want to align it with 3 vectors (i, j, k). I have read a bit about rotation matrices and I think that is what I will be needing but how can I construct one with this data?
Thanks in advance
I think you’d be surprised how easy that is 
Let i,j,k be normalised vectors representing local x,y,z then:
m = mathutils.Matrix(i.xyz,j.xyz,k.xyz)
ob.matrix_world = m.resize4x4()
If you want to maintain ob’s original location:
m = mathutils.Matrix(i.xyz,j.xyz,k.xyz)
ob.matrix_world = mathutils.Matrix.Translation(ob.location) * m.resize4x4()
It seems to depend what type i,j,k really are.
I got this working:
import bpy
import mathutils
from mathutils import *
i = Vector((1,1,1))
j = Vector((1,2,3))
k = Vector((0,0,4))
m = Matrix((tuple(i.xyz),tuple(j.xyz),tuple(k.xyz))).resize4x4()
print(m)
cube = bpy.context.active_object #default Cube
cube.matrix_world = m
EDIT:
tuple and .xyz may be removed 
This suffices: m = Matrix((i,j,k)).resize4x4() #see extra ( and ) !!
Hi, thanks for the replys. Both these replys work for Mesh Objects, but I don’t see how they work on meshes. My situation is that I have a list of vertices and I want to rotate all of them by an unknown amount to align the mesh formed by these vertices to another mesh. I already have the three vectors(i, j, and k) which represent the rotation of the vertices relative to their object. And I know the new vertices(the once I wont to rotate) are presently aligned to their objects local axies.
So, I wont to change the rotation of the mesh without affecting the rotation of the object. Dose that make sense or am I being confusing?
Ok, that makes perfect sense. Suppose we have object ob of which we want to rotate the mesh data with matrix m:
me = ob.data
for v in me.vertices:
v.co = m * v.co
Note that this will rotate the verts around the mesh origin.
Ah, I see, Thanks
Latest Blender you MUST reverse the matrix-vector product into vector*matrix!
“Latest Blender you MUST reverse the matrix-vector product into vector*matrix!”
PKHG you just saved my life! I couldn’t make something work and then a bell went off in the back of my head to this thread. Sometimes it’s easy to forget that 1x3 * 3x3 is ok but 3x3 * 1x3 is not!
that would be basic matrix math
you 3X 3 times 1X3 cannot be done or exist in math !
as long as you read the right way like 1 X 3 is 1 row X 1 col
happy 2.5
Whose bright idea was that? It is the near-universal mathematical convention that ordinary coordinate vectors are columns and matrices act on them from the left. Violating this expectation is very bad API design - especially when it was correct before!
Best wishes,
Matthew