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diff --git a/hw6/src/transformation3d.cpp b/hw6/src/transformation3d.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 "transformation3d.h"
+
+
+//////////////////
+// Constructors //
+//////////////////
+transformation3d::transformation3d(void)
+{
+  _translation = vec3d();
+  _transformation = mat3d(1.0f);
+  _inverseTransformation = mat3d(1.0f);
+}
+
+
+transformation3d::transformation3d(const vec3d& translation, const mat3d& transformation, const mat3d& inverseTransformation)
+{
+  _translation = translation;
+  _transformation = transformation;
+  _inverseTransformation = inverseTransformation;
+}
+
+
+transformation3d::transformation3d(const transformation3d& t)
+{
+  _translation = t._translation;
+  _transformation = t._transformation;
+  _inverseTransformation = t._inverseTransformation;
+}
+
+
+//////////////
+// Operator //
+//////////////
+transformation3d& transformation3d::operator=(const transformation3d& t)
+{
+  _assign(t);
+  return *this;
+}
+
+
+transformation3d transformation3d::operator*(const transformation3d& t) const
+{
+  return transformation3d( transformPoint(t._translation),
+			   _transformation * t._transformation,
+			   t._inverseTransformation * _inverseTransformation);
+}
+
+
+transformation3d& transformation3d::operator*=(const transformation3d& t)
+{
+  *this = *this * t;
+  return *this;
+}
+
+
+//////////////
+// Mutators //
+//////////////
+transformation3d& transformation3d::invert(void)
+{
+  _translation = _inverseTransformation * (-_translation);
+  swap(_transformation, _inverseTransformation);
+  return *this;
+}
+
+/////////////
+// Methods //
+/////////////
+vec3d transformation3d::transformPoint(const vec3d& p) const
+{
+  // first transform, then translate
+  vec3d transformed = _transformation * p;
+  transformed += _translation;
+  
+  // Done.
+  return transformed;
+}
+
+
+vec3d transformation3d::transformDirection(const vec3d& d) const
+{
+  // Only apply transformation
+  vec3d transformed = _transformation * d;
+
+  // Done.
+  return transformed.normalize();
+}
+
+
+vec3d transformation3d::transformNormal(const vec3d& n) const
+{
+  // Don't apply translation.
+  // n' = (_transformation^T)^-1 * n
+  // n'^T = n^T * _transformation^-1
+  // n'^T = n^T * _inverseTransformation
+  vec3d transformed = n * _inverseTransformation;
+  
+  // Done.
+  return transformed.normalize();
+}
+
+
+vec3d transformation3d::inverseTransformPoint(const vec3d& p) const
+{
+  // for undo translation, then invert the transformation
+  vec3d transformed = p - _translation;
+  transformed = _inverseTransformation * transformed;
+
+  // Done.
+  return transformed;
+}
+
+
+vec3d transformation3d::inverseTransformDirection(const vec3d& d) const
+{
+  // Only invert the transformation
+  vec3d transformed = _inverseTransformation * d;
+
+  // Done.
+  return transformed.normalize();
+}
+
+
+vec3d transformation3d::inverseTransformNormal(const vec3d& n) const
+{
+  // Don't apply translation. Undo (transformation^T)^-1
+  vec3d transformed = n * _transformation;
+
+  // Done.
+  return transformed.normalize();
+}
+
+
+///////////////////////
+// Protected Methods //
+///////////////////////
+void transformation3d::_swap(transformation3d& t)
+{
+  std::swap(_translation, t._translation);
+  std::swap(_transformation, t._transformation);
+  std::swap(_inverseTransformation, t._inverseTransformation);
+}
+
+
+void transformation3d::_assign(const transformation3d& t)
+{
+  // avoid copying when self-assigning
+  if(&t == this) return;
+
+  // Copy
+  _translation = t._translation;
+  _transformation = t._transformation;
+  _inverseTransformation = t._inverseTransformation;
+
+  // Done.
+}
+
+
+void transformation3d::_print(std::ostream& s) const
+{
+  s << "{";
+  s << "Translation = " << _translation << ", ";
+  s << "Transformation = " << _transformation << ", ";
+  s << "Inverse Trans. = " << _inverseTransformation;
+  s << "}";
+}