2010/3/1 Charles R Harris <charlesr.harris@gmail.com>:
On Sun, Feb 28, 2010 at 7:58 PM, Ian Mallett <geometrian@gmail.com> wrote:
Excellent--and a 3D rotation matrix is 3x3--so the list can remain n*3. Now the question is how to apply a rotation matrix to the array of vec3?
It looks like you want something like
res = dot(vec, rot) + tran
You can avoid an extra copy being made by separating the parts
res = dot(vec, rot) res += tran
where I've used arrays, not matrices. Note that the rotation matrix multiplies every vector in the array.
When you want to rotate a ndarray "list" of vectors:
a.shape (N, 3)
a [[1., 2., 3. ] [4., 5., 6. ]]
by some rotation matrix:
rotation_matrix.shape (3, 3)
where each row of the rotation_matrix represents one vector of the rotation target basis, expressed in the basis of the original system, you can do this by writing:
numpy.dot(a, rotations_matrix) ,
as Chuck pointed out. This gives you the rotated vectors in an ndarray "list" again:
numpy.dot(a, rotation_matrix).shape (N, 3)
This is just somewhat more in detail what Chuck already stated
Note that the rotation matrix multiplies every vector in the array.
my 2 cents, Friedrich