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

5.1.2.3  Picture Descriptor elements.  The Picture Descriptor Elements set the interpretation modes of the attribute elements.

5.1.2.3.1  Color Selection Mode element output.  The CGM implementation for NITFS shall provide the capability to generate and output the Color Selection Mode element using the following format.

TABLE LXXXI.  Color Selection Mode output.

MSB                                                                                                                                                               LSB

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

2                                                            2                                                                  2                                 = 0x2042

1                                                                                                =0x0001

5.1.2.3.2  Edge Width Specification Mode element output.  The CGM implementation for NITFS shall provide the capability to generate and output the Edge Width Specification Mode element using the following format.  Edge width is specified in "absolute mode," which indicates that the width is specified in pixels.  This command is used to support filled-area primitives.

TABLE LXXXII.  Edge Width Specification Mode output.

MSB                                                                                                                                                               LSB

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

2                                                            5                                                                  2                                 = 0x20A2

0                                                                                                =0x0000

5.1.2.3.3  Line Width Specification Mode element output.  The CGM implementation for NITFS shall provide the capability to generate and output the Line Width Specification Mode element using the following format.  Line width is specified in "absolute mode," which indicates that the width is specified in pixels.  This command is used to support the Polyline primitive.

TABLE LXXXIII.  Line Width Specification Mode output.

MSB                                                                                                                                                               LSB

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

2                                                            3                                                                  2                                 = 0x2062

0                                                                                                =0x0000

5.1.2.3.4  VDC Extent element output.  The CGM implementation for NITFS shall provide the capability to generate and output the VDC Extent element using the following format.

TABLE LXXXIV.  VDC Extent output.

X1

Y1

X2

Y2

This element (illustrated on figures 4 and 5) defines the rectangular extent of the VDC space and the orientation of VDC space (the direction of the positive X and positive Y axes).  The extent and orientation of VDC space is indicated by giving the coordinates of lower left hand and upper right hand corners of the VDC extent.  The VDC extent space is a one-to-one map from the VDC extent to the source coordinates.  The VDC extent origin (0,0) is mapped onto the source at the row and column location given by the SLOC field in the Symbol Subheader for a given image.  The Symbol Subheader and the SLOC field are defined in the MIL-STD-2500 document.  Note that X1 and X2 cannot be equal, and Y1 and Y2 cannot be equal.  Note that the proper Character Orientation element must be present to ensure that CGM text is orientated right side up for a given VDC Extent element.

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