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diff --git a/src/vector.cpp b/src/vector.cpp
index e9ad51f..23bd783 100644
--- a/src/vector.cpp
+++ b/src/vector.cpp
@@ -1,7 +1,7 @@
 //
 // vector.cpp: Various structures used for 3 dimensional imaging
 //
-// by James L. Hammons
+// by James Hammons
 // (C) 2006 Underground Software
 //
 // JLH = James L. Hammons <jlhamm@acm.org>
@@ -11,6 +11,7 @@
 // JLH  09/19/2006  Created this file
 // JLH  03/22/2011  Moved implementation of constructor from header to here
 // JLH  04/02/2011  Fixed divide-by-zero bug in Unit(), added Angle() function
+// JLH  08/04/2013  Added Parameter() function
 //
 
 #include "vector.h"
@@ -18,17 +19,18 @@
 #include <math.h>								// For sqrt()
 #include "mathconstants.h"
 
-
 // Vector implementation
 
 Vector::Vector(double xx/*= 0*/, double yy/*= 0*/, double zz/*= 0*/): x(xx), y(yy), z(zz)
 {
 }
 
+
 Vector::Vector(Vector head, Vector tail): x(head.x - tail.x), y(head.y - tail.y), z(head.z - tail.z)
 {
 }
 
+
 Vector Vector::operator=(Vector const v)
 {
 	x = v.x, y = v.y, z = v.z;
@@ -36,16 +38,19 @@ Vector Vector::operator=(Vector const v)
 	return *this;
 }
 
+
 Vector Vector::operator+(Vector const v)
 {
 	return Vector(x + v.x, y + v.y, z + v.z);
 }
 
+
 Vector Vector::operator-(Vector const v)
 {
 	return Vector(x - v.x, y - v.y, z - v.z);
 }
 
+
 // Unary negation
 
 Vector Vector::operator-(void)
@@ -53,6 +58,7 @@ Vector Vector::operator-(void)
 	return Vector(-x, -y, -z);
 }
 
+
 // Vector x constant
 
 Vector Vector::operator*(double const v)
@@ -60,6 +66,7 @@ Vector Vector::operator*(double const v)
 	return Vector(x * v, y * v, z * v);
 }
 
+
 // Vector x constant
 
 Vector Vector::operator*(float const v)
@@ -67,6 +74,7 @@ Vector Vector::operator*(float const v)
 	return Vector(x * v, y * v, z * v);
 }
 
+
 // Vector / constant
 
 Vector Vector::operator/(double const v)
@@ -74,6 +82,7 @@ Vector Vector::operator/(double const v)
 	return Vector(x / v, y / v, z / v);
 }
 
+
 // Vector / constant
 
 Vector Vector::operator/(float const v)
@@ -81,6 +90,7 @@ Vector Vector::operator/(float const v)
 	return Vector(x / v, y / v, z / v);
 }
 
+
 // Vector (cross) product
 
 Vector Vector::operator*(Vector const v)
@@ -89,6 +99,7 @@ Vector Vector::operator*(Vector const v)
 	return Vector((y * v.z) - (z * v.y), (z * v.x) - (x * v.z), (x * v.y) - (y * v.x));
 }
 
+
 // Dot product
 
 double Vector::Dot(Vector const v)
@@ -106,6 +117,7 @@ Vector& Vector::operator*=(double const v)
 	return *this;
 }
 
+
 // Vector / constant, self assigned
 
 Vector& Vector::operator/=(double const v)
@@ -124,6 +136,7 @@ Vector& Vector::operator+=(Vector const v)
 	return *this;
 }
 
+
 // Vector + constant, self assigned
 
 Vector& Vector::operator+=(double const v)
@@ -134,6 +147,40 @@ Vector& Vector::operator+=(double const v)
 }
 
 
+// Vector - vector, self assigned
+
+Vector& Vector::operator-=(Vector const v)
+{
+	x -= v.x, y -= v.y, z -= v.z;
+
+	return *this;
+}
+
+
+// Vector - constant, self assigned
+
+Vector& Vector::operator-=(double const v)
+{
+	x -= v, y -= v, z -= v;
+
+	return *this;
+}
+
+
+// Check for equality
+bool Vector::operator==(Vector const v)
+{
+	return (x == v.x && y == v.y && z == v.z ? true : false);
+}
+
+
+// Check for inequality
+bool Vector::operator!=(Vector const v)
+{
+	return (x != v.x || y != v.y || z != v.z ? true : false);
+}
+
+
 Vector Vector::Unit(void)
 {
 	double mag = Magnitude();
@@ -145,11 +192,13 @@ Vector Vector::Unit(void)
 	return Vector(x / mag, y / mag, z / mag);
 }
 
+
 double Vector::Magnitude(void)
 {
 	return sqrt(x * x + y * y + z * z);
 }
 
+
 double Vector::Angle(void)
 {
 	// acos returns a value between zero and PI, which means we don't know which
@@ -161,6 +210,7 @@ double Vector::Angle(void)
 	return correctedAngle;
 }
 
+
 bool Vector::isZero(double epsilon/*= 1e-6*/)
 {
 	return (fabs(x) < epsilon && fabs(y) < epsilon && fabs(z) < epsilon ? true : false);
@@ -174,6 +224,7 @@ double Vector::Dot(Vector v1, Vector v2)
 	return (v1.x * v2.x) + (v1.y * v2.y) + (v1.z * v2.z);
 }
 
+
 double Vector::Magnitude(Vector v1, Vector v2)
 {
 	double xx = v1.x - v2.x;
@@ -181,3 +232,31 @@ double Vector::Magnitude(Vector v1, Vector v2)
 	double zz = v1.z - v2.z;
 	return sqrt(xx * xx + yy * yy + zz * zz);
 }
+
+
+// Returns the parameter of a point in space to this vector. If the parameter
+// is between 0 and 1, the normal of the vector to the point is on the vector.
+double Vector::Parameter(Vector v1, Vector v2, Vector p)
+{
+	// Geometric interpretation:
+	// The parameterized point on the vector lineSegment is where the normal of
+	// the lineSegment to the point intersects lineSegment. If the pp < 0, then
+	// the perpendicular lies beyond the 1st endpoint. If pp > 1, then the
+	// perpendicular lies beyond the 2nd endpoint.
+
+	Vector lineSegment = v2 - v1;
+	double magnitude = lineSegment.Magnitude();
+	Vector pointSegment = p - v1;
+	double t = lineSegment.Dot(pointSegment) / (magnitude * magnitude);
+	return t;
+}
+
+
+// Return the normal to the linesegment formed by the passed in points.
+// (Not sure which is head or tail, or which hand the normal lies)
+/*static*/ Vector Vector::Normal(Vector v1, Vector v2)
+{
+	Vector v = (v2 - v1).Unit();
+	return Vector(-v.y, v.x);
+}
+