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

d.  Metafile Graphical Primitives with Associated Attributes

Text Primitive Element with Attributes

TEXT COLOR CHARACTER HEIGHT TEXT FONT INDEX

CHARACTER ORIENTATION TEXT

Filled-Area Primitive Elements with Attributes

FILL COLOR

INTERIOR STYLE (1= solid, 3=hatch, or 4 = empty) EDGE VISIBILITY (0=off, 1 = on)

EDGE WIDTH

EDGE TYPE (1=solid, 2=dashed, 3=dot, 4=dash-dot, 5=dash-dot-dot) EDGE COLOR

POLYGON POLYGON SET ELLIPSE

ELLIPTICAL ARC CLOSE RECTANGLE

CIRCLE

CIRCULAR ARC CENTER CLOSE Line Primitive Elements with Attributes

LINE WIDTH

LINE TYPE (1=solid, 2=dashed, 3=dot, 4=dash-dot, 5=dash-dot-dot) LINE COLOR

POLYLINE ELLIPTICAL ARC CIRCULAR ARC CENTER

e.  Metafile Control Elements TRANSPARENCY AUXILIARY COLOR

4.2  CGM binary encoding.  CGM commands in the CGM implementation for NITFS are encoded using the binary encoding method described in the FIPS PUB 128.  Metafile elements will be represented in the binary encoding in either short-form commands or long-form commands.  For short-form and long-form commands, the 4 most significant bits (MSB) identify the element class in which the command belongs (for example, Delimiter Elements, Descriptor Elements) and the fifth through eleventh bits identify the element ID (for example, BEGIN METAFILE, END METAFILE).  For the short-form command, the five least significant bits (LSB) specify the length, in bytes, of the parameter list.  This form is used to specify parameter lists that are less than 31 LONG.  For the long-form command, the 5 LSB are set to the binary value "11111" (decimal 31).  In this case, the next 2 bytes are interpreted as a signed positive integer containing the length of the parameter list.  For short-form and

long-form commands, the first byte of a string parameter specifies the length of the string.  If necessary, parameters are padded with a trailing null byte (0) to ensure that all subsequent commands begin on a 16-bit word boundary.  Note, the trailing null byte is not included in the parameter list length.  In the figures contained in this standard, all numbers are decimal unless preceded by "0x" indicating hexadecimal notation.

TABLE I.  Short form of CGM command.

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