added a plane geometry function

miscmaths.h

@@ -167,6 +167,11 @@ namespace MISCMATHS {
   void cart2sph(const Matrix& dir,ColumnVector& th,ColumnVector& ph);//ditto
   void cart2sph(const vector<ColumnVector>& dir,ColumnVector& th,ColumnVector& ph);// same but in a vector
 
+  // geometry function
+  inline float point_plane_distance(const ColumnVector& X,const ColumnVector& P){//plane defined by a,b,c,d with a^2+b^2+c^2=1
+    return( dot(X,P.SubMatrix(1,3,1,1))+P(4) );
+  }
+
   // returns the first P such that 2^P >= abs(N). 
   int nextpow2(int n);