diff --git a/vcg/math/matrix33.h b/vcg/math/matrix33.h
index faff3f5e..a9160ff6 100644
--- a/vcg/math/matrix33.h
+++ b/vcg/math/matrix33.h
@@ -8,7 +8,7 @@
 *                                                                    \      *
 * All rights reserved.                                                      *
 *                                                                           *
-* This program is free software; you can redistribute it and/or modify      *   
+* This program is free software; you can redistribute it and/or modify      *
 * it under the terms of the GNU General Public License as published by      *
 * the Free Software Foundation; either version 2 of the License, or         *
 * (at your option) any later version.                                       *
@@ -103,10 +103,10 @@ namespace vcg {
 template <class S>
 class Matrix33Diag:public Point3<S>{
 public:
-	
+
 	/** @name Matrix33
 	Class Matrix33Diag.
-    This is the class for definition of a diagonal matrix 3x3.	
+    This is the class for definition of a diagonal matrix 3x3.
 	@param S (Templete Parameter) Specifies the ScalarType field.
 */
 	Matrix33Diag(const S & p0,const S & p1,const S & p2):Point3<S>(p0,p1,p2){};
@@ -116,14 +116,14 @@ public:
 template<class S>
 /** @name Matrix33
 	Class Matrix33.
-    This is the class for definition of a matrix 3x3.	
+    This is the class for definition of a matrix 3x3.
 	@param S (Templete Parameter) Specifies the ScalarType field.
 */
 class Matrix33
 {
 public:
 	typedef S ScalarType;
-	
+
 	/// Default constructor
 	inline Matrix33() {}
 
@@ -172,7 +172,7 @@ public:
 	}
 
 
-	
+
 	/// Operatore di indicizzazione
 	inline S * operator [] ( const int i )
 	{
@@ -183,7 +183,7 @@ public:
 	{
 		return a+i*3;
 	}
-	
+
 
 	/// Modificatore somma per matrici 3x3
 	Matrix33 & operator += ( const Matrix33  &m )
@@ -209,7 +209,7 @@ public:
 			a[i] -= m.a[i];
 		return *this;
 	}
-	
+
 	/// Modificatore somma per matrici 3x3
 	Matrix33 & operator -= ( const Matrix33Diag<S>  &p )
 	{
@@ -236,18 +236,18 @@ public:
 		int i,j;
 		for(i=0;i<3;++i)
 			for(j=0;j<3;++j)
-					r[i][j] = (*this)[i][0]*t[0][j] + (*this)[i][1]*t[1][j] + (*this)[i][2]*t[2][j]; 
+					r[i][j] = (*this)[i][0]*t[0][j] + (*this)[i][1]*t[1][j] + (*this)[i][2]*t[2][j];
 
 		return r;
 	}
 
 	/// Modificatore prodotto per matrice
-	void operator *=( const Matrix33< S> & t ) 
+	void operator *=( const Matrix33< S> & t )
 	{
 		int i,j;
 		for(i=0;i<3;++i)
 			for(j=0;j<3;++j)
-					(*this)[i][j] = (*this)[i][0]*t[0][j] + (*this)[i][1]*t[1][j] + (*this)[i][2]*t[2][j]; 
+					(*this)[i][j] = (*this)[i][0]*t[0][j] + (*this)[i][1]*t[1][j] + (*this)[i][2]*t[2][j];
 
 	}
 
@@ -259,18 +259,18 @@ public:
 		int i,j;
 		for(i=0;i<3;++i)
 			for(j=0;j<3;++j)
-					r[i][j] = (*this)[i][j]*t[j]; 
+					r[i][j] = (*this)[i][j]*t[j];
 
 		return r;
 	}
 
 		/// Dot product modifier with a diagonal matrix
-	void operator *=( const Matrix33Diag< S> & t ) 
+	void operator *=( const Matrix33Diag< S> & t )
 	{
 		int i,j;
 		for(i=0;i<3;++i)
 			for(j=0;j<3;++j)
-					(*this)[i][j] = (*this)[i][j]*t[j]; 
+					(*this)[i][j] = (*this)[i][j]*t[j];
 	}
 
 	/// Modificatore prodotto per costante
@@ -282,7 +282,7 @@ public:
 	}
 
 	/// Operatore prodotto per costante
-	Matrix33 operator * ( const S t )
+	Matrix33 operator * ( const S t ) const
 	{
 		Matrix33<S> r;
 		for(int i=0;i<9;++i)
@@ -292,7 +292,7 @@ public:
 	}
 
 	/// Operatore sottrazione per matrici 3x3
-	Matrix33  operator - ( const Matrix33 &m )
+	Matrix33  operator - ( const Matrix33 &m ) const
 	{
 		Matrix33<S> r;
 		for(int i=0;i<9;++i)
@@ -300,9 +300,9 @@ public:
 
 		return r;
 	}
-	
+
 	/// Operatore sottrazione di matrici 3x3 con matrici diagonali
-	Matrix33  operator - ( const Matrix33Diag<S>  &p )
+	Matrix33  operator - ( const Matrix33Diag<S>  &p ) const
 	{
 		Matrix33<S> r=a;
 		r[0][0] -= p[0];
@@ -312,7 +312,7 @@ public:
 	}
 
 	/// Operatore sottrazione per matrici 3x3
-	Matrix33  operator + ( const Matrix33 &m )
+	Matrix33  operator + ( const Matrix33 &m ) const
 	{
 		Matrix33<S> r;
 		for(int i=0;i<9;++i)
@@ -320,9 +320,9 @@ public:
 
 		return r;
 	}
-	
+
 	/// Operatore addizione di matrici 3x3 con matrici diagonali
-	Matrix33  operator + ( const Matrix33Diag<S>  &p )
+	Matrix33  operator + ( const Matrix33Diag<S>  &p ) const
 	{
 		Matrix33<S> r=(*this);
 		r[0][0] += p[0];
@@ -502,10 +502,10 @@ S Trace() const
 	return a[0]+a[4]+a[8];
 }
 
-/* 
+/*
 compute the matrix generated by the product of a * b^T
 */
-void ExternalProduct(const Point3<S> &a, const Point3<S> &b) 
+void ExternalProduct(const Point3<S> &a, const Point3<S> &b)
 {
 	for(int i=0;i<3;++i)
 		for(int j=0;j<3;++j)
@@ -524,8 +524,8 @@ ScalarType Norm()
 }
 
 
-/* 
-It compute the  covariance matrix of a set of 3d points. Returns the barycenter 
+/*
+It compute the  covariance matrix of a set of 3d points. Returns the barycenter
 */
 template <class STLPOINTCONTAINER >
 void Covariance(const STLPOINTCONTAINER &points, Point3<S> &bp) {
@@ -547,19 +547,19 @@ void Covariance(const STLPOINTCONTAINER &points, Point3<S> &bp) {
 
 
 
-/* 
+/*
 It compute the cross covariance matrix of two set of 3d points P and X;
 it returns also the barycenters of P and X.
 fonte:
 
 Besl, McKay
-A method for registration o f 3d Shapes 
+A method for registration o f 3d Shapes
 IEEE TPAMI Vol 14, No 2 1992
 
-*/ 
+*/
 template <class STLPOINTCONTAINER >
-void CrossCovariance(const STLPOINTCONTAINER &P, const STLPOINTCONTAINER &X, 
-										 Point3<S> &bp, Point3<S> &bx) 
+void CrossCovariance(const STLPOINTCONTAINER &P, const STLPOINTCONTAINER &X,
+										 Point3<S> &bp, Point3<S> &bx)
 {
 	SetZero();
 	assert(P.size()==X.size());
@@ -582,10 +582,10 @@ void CrossCovariance(const STLPOINTCONTAINER &P, const STLPOINTCONTAINER &X,
 
 template <class STLPOINTCONTAINER, class STLREALCONTAINER>
 void WeightedCrossCovariance(const STLREALCONTAINER &  weights,
-							 const STLPOINTCONTAINER &P, 
-							 const STLPOINTCONTAINER &X, 
-							 Point3<S> &bp, 
-							 Point3<S> &bx) 
+							 const STLPOINTCONTAINER &P,
+							 const STLPOINTCONTAINER &X,
+							 Point3<S> &bp,
+							 Point3<S> &bx)
 {
 	SetZero();
 	assert(P.size()==X.size());
@@ -603,7 +603,7 @@ void WeightedCrossCovariance(const STLREALCONTAINER &  weights,
 	bx/=X.size();
 
 	for(pi=P.begin(),xi=X.begin(),pw = weights.begin();pi!=P.end();++pi,++xi,++pw){
-		
+
 		tmp.ExternalProduct(((*pi)-(bp)),((*xi)-(bp)));
 
 		(*this)+=tmp*(*pw);
@@ -656,11 +656,11 @@ Matrix33<S> RotationMatrix(vcg::Point3<S> v0,vcg::Point3<S> v1,bool normalized=t
 			return rotM;
 		}
 
-		///find the axis of rotation 
+		///find the axis of rotation
 		CoordType axis;
 		axis=v0^v1;
 		axis.Normalize();
-		
+
 		///construct rotation matrix
 		S u=axis.X();
 		S v=axis.Y();
@@ -668,7 +668,7 @@ Matrix33<S> RotationMatrix(vcg::Point3<S> v0,vcg::Point3<S> v1,bool normalized=t
 		S phi=acos(dot);
 		S rcos = cos(phi);
 		S rsin = sin(phi);
-		
+
 		rotM[0][0] =      rcos + u*u*(1-rcos);
 		rotM[1][0] =  w * rsin + v*u*(1-rcos);
 		rotM[2][0] = -v * rsin + w*u*(1-rcos);
@@ -725,7 +725,7 @@ template <class S>
 	return M;
 }
 
-/// 
+///
 typedef Matrix33<short>  Matrix33s;
 typedef Matrix33<int>	 Matrix33i;
 typedef Matrix33<float>  Matrix33f;