MIL-STD-2301 Computer Graphics Metafile Cgm Implementation Standard For The National Imagery Transmission Format StandardThis standard establishes the requirements necessary to implement Computer Graphics Metafiles CGM used for the representation of symbol graphics in the National Imagery Transmission Format Standard NITFS.

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MIL-STD-2301A

TABLE CI.  Text nonpadded, long form output.

MSB                                                                                                                                                               LSB

15        14      13       12       11       10        9         8         7         6          5         4         3          2       1         0

4                                                            4                                                                 31                                  0x409F

parameter list length

X Y

1                                                                                                 0x0001 length = n (odd)                                                                           C1

C2                                                                                       .

C(n-1)                                                                                  Cn

5.1.2.5.2  Polygon element output.  The CGM implementation for NITFS shall provide the capability to generate and output the Polygon element using the following format.  The polygon parameters consist of a list of pairs of coordinates indicating the vertices of a polygon.  The first vertex (Vertex1X, Vertex1Y) is connected to the last (Vertex(N)X, Vertex(N)Y) to close the polygon.  Polygons are not "clipped" to the image boundary.  Therefore, some coordinates may specify off-image or off-screen locations, including negative locations.  Note, the parameter list length is given as the total number of bytes for all vertex  parameters (4N).

TABLE CII.  Polygon short form output.

MSB                                                                                                                                                                          LSB

15       14      13        12        11        10         9          8          7          6          5          4          3          2          1          0

1                7                                                  parameter list length (4N) Vertex1X

Vertex1Y Vertex2X Vertex2Y

.

.

.

Vertex(N)X Vertex(N)Y

TABLE CIII.  Polygon long form output.

MSB                                                                                                                                                               LSB

15        14      13       12       11       10        9         8         7         6          5         4         3          2       1         0

4                7                                                                 31                                  0x40FF Parameter list length (4N)

Vertex1X Vertex1Y Vertex2X Vertex2Y

.

.

. Vertex(N)X Vertex(N)Y

5.1.2.5.2.1  Polygon Set element output.  The CGM implementation for NITFS shall provide the capability to generate and output the Polygon Set element using the following format.  The polygon set parameters consist of a list of pairs of coordinates indicating the vertices of each polygon in the polygon set along with the Edge_Out_Flag indicating the edge visibility and whether the vertex is the last (closure) vertex of the specific polygon in the set.  The first vertex of the first polygon (Vertex_11X, Vertex_11Y, Edge_Out_Flag_11) is connected to the last  (Vertex_1(N)X, Vertex_1(N)Y, Edge_Out_Flag_1(N)) vertex in the first polygon followed by the vertices of each successive polygon in like manner.  Polygon Sets are not "clipped" to the image boundary; therefore, some coordinates may specify off-image or off-screen locations, including negative locations.  The Edge_Out_Flag parameter can be Invisible (0), Visible (1), Close Invisible (2), or Close Visible (3).  Note, the

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