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diff --git a/hw6/src/coordinateTransform.cpp b/hw6/src/coordinateTransform.cpp
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+++ b/hw6/src/coordinateTransform.cpp
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+/******************************************************************/
+/* This file is part of the homework assignments for CSCI-427/527 */
+/* at The College of William & Mary and authored by Pieter Peers. */
+/* No part of this file, whether altered or in original form, can */
+/* be distributed or used outside the context of CSCI-427/527     */
+/* without consent of either the College of William & Mary or     */
+/* Pieter Peers.                                                  */
+/******************************************************************/
+#include "coordinateTransform.h"
+
+//////////////////
+// Constructors //
+//////////////////
+coordinateTransformation::coordinateTransformation(void)
+{
+  // do nothing
+}
+
+
+coordinateTransformation::coordinateTransformation(const vec3d& normal)
+{
+  // normal == Z axis
+  vec3d X, Y, Z = normalize(normal);
+  
+  // select Y axis
+  if(fabs(Z.x) < fabs(Z.y) && fabs(Z.x) < fabs(Z.z))
+    Y = normalize(vec3d(0.0f, Z.z, -Z.y));
+  else if(fabs(Z.y) < fabs(Z.z))
+    Y = normalize(vec3d(Z.z, 0.0f, -Z.x));
+  else
+    Y = normalize(vec3d(Z.y, -Z.x, 0.0f));
+  
+  // create other axis
+  X = Y.cross(Z).normalize();
+
+  // copy
+  _transformation = mat3d(X, Y, Z);
+  _inverseTransformation = transpose(_transformation);
+
+  // Done.
+}
+
+
+coordinateTransformation::coordinateTransformation(const vec3d& normal, const vec3d& axis)
+{
+  // normal == Z axis
+  vec3d Z = normalize(normal);
+  
+  // create other axis
+  vec3d axis_normalized = normalize(axis);
+  vec3d Y = Z.cross(axis_normalized).normalize();
+  vec3d X = Y.cross(Z).normalize();
+
+  // copy
+  _transformation = mat3d(X, Y, Z);
+  _inverseTransformation = transpose(_transformation);
+
+  // Done.
+}
+
+
+coordinateTransformation::coordinateTransformation(const vec3d& X, const vec3d& Y, const vec3d& Z)
+{
+  // trust user to provide an orthogonal set of vectors.
+  _transformation = mat3d(X, Y, Z);
+  _inverseTransformation = transpose(_transformation);
+}