public static Matrix3d P2M(this Viewport vp)
 {
     if (vp.PerspectiveOn)
     {
         return(new Matrix3d());
     }
     if (vp.Number == 1)
     {
         return(new Matrix3d());
     }
     return(vp.Dcs2Wcs() * vp.Dcs2Psdcs().Inverse());
 }
 /// <summary>
 ///     Gets the transformation matrix from the Paper Space Display Coordinate System (PSDCS)
 ///     to the specified paper space viewport Display Coordinate System (DCS).
 /// </summary>
 /// <param name="vp">The instance to which this method applies.</param>
 /// <returns>The PSDCS to DCS transformation matrix.</returns>
 public static Matrix3d Psdcs2Dcs(this Viewport vp)
 {
     return(vp.Dcs2Psdcs().Inverse());
 }