grd_type: grd_polygon
GRD polygon features represent closed polygonal features and may be either 2D or 3D. These features do not have any special attributes associated with them.
grd_type: grd_rectangle
GRD rectangle features represent closed polygonal features, containing only four points, that make up a polygon. These rectangles cannot have any rotation—their edges must be horizontal or vertical. These features may be either 2D or 3D, and do not have any special attributes associated with them.