1 files changed, 20 insertions, 0 deletions
diff --git a/transform.py b/transform.py
new file mode 100644
index 0000000..4793c0f
--- /dev/null
+++ b/transform.py
@@ -0,0 +1,20 @@
+import numpy as np
+
+def make_rotation_matrix(phi, n):
+    """
+    Make the rotation matrix to rotate points through an angle `phi`
+    counter-clockwise around the axis `n` (when looking towards +infinity).
+
+    Source: Weissten, Eric W. "Rotation Formula." Mathworld.
+    """
+    n = np.asarray(n)/np.linalg.norm(n)
+    
+    return np.cos(phi)*np.identity(3) + (1-np.cos(phi))*np.outer(n,n) + \
+        np.sin(phi)*np.array([[0,n[2],-n[1]],[-n[2],0,n[0]],[n[1],-n[0],0]])
+
+def rotate(x, phi, n):
+    """
+    Rotate an array of points `x` through an angle phi counter-clockwise
+    around the axis `n` (when looking towards +infinity).
+    """
+    return np.inner(np.asarray(x),make_rotation_matrix(phi, n))