diff --git a/util/Transform.cc b/util/Transform.cc
index 115a3e2..ec1f8ff 100644
--- a/util/Transform.cc
+++ b/util/Transform.cc
@@ -1,5 +1,6 @@
 
 #include "Transform.h"
+#include <math.h>
 
 Transform::Transform()
 {
@@ -15,9 +16,33 @@ void Transform::translate(double x, double y, double z)
     m_matrix *= t;
 }
 
-void Transform::rotate(double amt, double xv, double yv, double zv)
+void Transform::rotate(double angle, double xv, double yv, double zv)
 {
-    /* TODO: fill in */
+    /* formula from http://en.wikipedia.org/wiki/Rotation_matrix */
+    Vector l(xv, yv, zv);
+    l.normalize();
+
+    double c = cos(angle);
+    double s = sin(angle);
+
+    double lx2 = l[0] * l[0];
+    double ly2 = l[1] * l[1];
+    double lz2 = l[2] * l[2];
+
+    Matrix t = Matrix::identity();
+    t[0][0] = lx2 + (1 - lx2) * c;
+    t[0][1] = l[0] * l[1] * (1 - c) - l[2] * s;
+    t[0][2] = l[0] * l[2] * (1 - c) + l[1] * s;
+
+    t[1][0] = l[0] * l[1] * (1 - c) + l[2] * s;
+    t[1][1] = ly2 + (1 - ly2) * c;
+    t[1][2] = l[1] * l[2] * (1 - c) - l[0] * s;
+
+    t[2][0] = l[0] * l[2] * (1 - c) - l[1] * s;
+    t[2][1] = l[1] * l[2] * (1 - c) + l[0] * s;
+    t[2][2] = lz2 + (1 - lz2) * c;
+
+    m_matrix *= t;
 }
 
 void Transform::scale(double xs, double ys, double zs)
diff --git a/util/Transform.h b/util/Transform.h
index ca3d75f..38a6242 100644
--- a/util/Transform.h
+++ b/util/Transform.h
@@ -10,7 +10,7 @@ class Transform
     public:
         Transform();
         void translate(double x, double y, double z);
-        void rotate(double amt, double xv, double yv, double zv);
+        void rotate(double angle, double xv, double yv, double zv);
         void scale(double xs, double ys, double zs);
         Matrix & getMatrix() { return m_matrix; }
 
diff --git a/util/Vector.cc b/util/Vector.cc
index b239769..2208d11 100644
--- a/util/Vector.cc
+++ b/util/Vector.cc
@@ -10,6 +10,13 @@ Vector::Vector()
     m_array[2] = 0.0;
 }
 
+Vector::Vector(double x, double y, double z)
+{
+    m_array[0] = x;
+    m_array[1] = y;
+    m_array[2] = z;
+}
+
 void Vector::normalize()
 {
     double length = sqrt(m_array[0] * m_array[0]
diff --git a/util/Vector.h b/util/Vector.h
index 084a1a7..0704d93 100644
--- a/util/Vector.h
+++ b/util/Vector.h
@@ -8,6 +8,7 @@ class Vector
 {
     public:
         Vector();
+        Vector(double x, double y, double z);
         double & operator[](int idx) { return m_array[idx]; }
         double operator[](int idx) const { return m_array[idx]; }
         void normalize();