Added edge::calc_angle()

Moved interior angle calculation to a separate function within the edge
class. This seems more elegant.

edge.cpp

@@ -4,7 +4,7 @@
 */
 
 #include <iostream>
-#include <cassert>
+#include <cmath>
 
 #include "edge.h"
 
@@ -222,4 +222,36 @@ void edge::set_on_boundary(bool boundary)
 	this->boundary = boundary;
 }
 
+/*!
+*	Given another edge that is assumed to share one vertex with the current
+*	edge, calculate the interior angle between these two edges.
+*
+*	@warning The result is undefined if both edges do _not_ share a common
+*	vertex.
+*
+*	@return Interior angle between edge e and current edge
+*/
+
+double edge::calc_angle(const edge* e) const
+{
+	// Check that both edges point into the _same_ direction -- otherwise
+	// the wrong angle would be calculated.
+
+	if(	this->get_u() == e->get_u() ||
+		this->get_v() == e->get_v())
+	{
+		v3ctor a = this->get_u()->get_position() - this->get_v()->get_position();
+		v3ctor b = e->get_u()->get_position() - e->get_v()->get_position();
+
+		return(acos(a.normalize()*b.normalize()));
+	}
+	else
+	{
+		v3ctor a = this->get_u()->get_position() - this->get_v()->get_position();
+		v3ctor b = e->get_v()->get_position() - e->get_u()->get_position(); // swap second edge
+
+		return(acos(a.normalize()*b.normalize()));
+	}
+}
+
 } // end of namespace "psalm"

edge.h

@@ -58,6 +58,7 @@ class edge
 		void set_on_boundary(bool boundary = true);
 
 		double calc_length() const;
+		double calc_angle(const edge* e) const;
 
 	private: