/**
  * A Point guaranteed to be on this MultiSurface.
  *
  * @return point on surface
  */
 public JTSPointExpression<Point> pointOnSurface() {
   if (pointOnSurface == null) {
     pointOnSurface = JTSGeometryExpressions.pointOperation(SpatialOps.POINT_ON_SURFACE, mixin);
   }
   return pointOnSurface;
 }
 /**
  * The mathematical centroid for this MultiSurface. The result is not guaranteed to be on this
  * MultiSurface.
  *
  * @return centroid
  */
 public JTSPointExpression<Point> centroid() {
   if (centroid == null) {
     centroid = JTSGeometryExpressions.pointOperation(SpatialOps.CENTROID, mixin);
   }
   return centroid;
 }