# NAME

GDX_POLY_SHELL - Polygon Shell Surface

# GENERAL DESCRIPTION

The GDX Polygon Shell entity is the collection of planar facets that linearly approximate a GDX Curve Bounded Surface or a GDX Face entity. The polygons are formed by checking the planarity of the facets that would produce a GDX_FACET_SHELL and, if the facet is not planar to within the planarity tolerance, splitting it into two planar polygons. Consequently, resulting polygons will always consist of 3 or 4 sides.

# DDF SPECIFICATION

    entity 33:0 GDX_POLY_SHELL "Polygon Shell Surface" {

    count
    NUM_POINTS;

    double
    POINTS[NUM_POINTS][3];

    double
    PARMS[NUM_POINTS][2];

    count
    NUM_BOUNDARY_POINTS;

    long
    BOUNDARY_POINTS[NUM_BOUNDARY_POINTS];

    count
    NUM_POLYGONS;

    struct
    POLYGONS[NUM_POLYGONS] {

    count
    NUM_POLYGON_PNTS;

    long
    POLYGON_PNTS[NUM_POLYGON_PNTS];

    };

    };

# FIELD DESCRIPTIONS

NUM_POINTS

The number of points in the GDX Polygon Shell.

POINTS

Array, dimensioned to [NUM_POINTS][3], containing values that define the model space points of the GDX Polygon Shell Surface.

PARMS

Array, dimensioned to [NUM_POINTS][2], containing values that define the parameter space points of the GDX Polygon Shell Surface.

~NUM_BOUNDARY_POINTS

The number of boundary points that define the inner and outter loop boundaries

~BOUNDARY_POINTS

Array, dimensioned to [~NUM_BOUNDARY_POINTS], containng indices of each point that define the inner/outter boundaries of the polyshell. The point indicies are referenced like arrays in the "C" programing lanquage. Thus, point indicies are in the range [0 to NUM_BOUNDARY_POINTS-1].

NUM_POLYGONS

The number of polygons in the faceted representation of the surface.

POLYGONS

Array, dimensioned to [NUM_POLYGONS], of structures containing the number of polygon points and the indices of each point that make up the facet polygons.

NUM_POLYGON_PNTS

The number of polygon points in the corresponding polygon.

POLYGON_PNTS

Array, dimensioned to [NUM_POLYGON_PNTS], containing point indices for the corresponding polygon. The point indicies are referenced like arrays in the "C" programing lanquage. Thus, point indicies are in the range [0 to NUM_POINTS-1].

# RESTRICTIONS

None.