ON_BOOL32 ON_LineCurve::IsInPlane( const ON_Plane& plane, // plane to test double tolerance // tolerance to use when checking linearity ) const { ON_BOOL32 rc = false; double d = fabs( plane.DistanceTo( PointAtStart() )); if ( d <= tolerance ) { d = fabs( plane.DistanceTo( PointAtEnd() )); if ( d <= tolerance ) rc = true; } return rc; }