om the point
       and normal, then convert the plane to a unit normal and constant.
       The constant is the distance of the plane from the origin. 
 
          <a href="nvp2pl_c.html">nvp2pl_c</a> ( normal, point,  &amp;plane    ); 
          <b>pl2nvc_c</b> ( &amp;plane, normal, &amp;constant ); 
 
 
   2)  Apply a linear transformation represented by the matrix m to 
       a plane represented by the normal vector n and the constant c. 
       Find a normal vector and constant for the transformed pla