


      GPS(4)                      (UNIX 5.2)                     GPS(4)



      NAME
           gps - graphical primitive string, format of graphical files

      DESCRIPTION
           GPS is a format used to store graphical data.  Several
           routines have been developed to edit and display GPS files
           on various devices.  Also, higher level graphics programs,
           such as plot (in stat(1)) and vtoc (in toc(1)), produce GPS
           format output files.

           A GPS is composed of five types of graphical data or
           primitives.

         GPS PRIMITIVES
           lines     The lines primitive has a variable number of
                     points from which zero or more connected line
                     segments are produced.  The first point given
                     produces a move to that location.  (A move is a
                     relocation of the graphic cursor without drawing.)
                     Successive points produce line segments from the
                     previous point.  Parameters are available to set
                     color, weight, and style (see below).

           arc       The arc primitive has a variable number of points
                     to which a curve is fit.  The first point produces
                     a move to that point.  If only two points are
                     included, a line connecting the points will
                     result; if three points, a circular arc through
                     the points is drawn; and if more than three, lines
                     connect the points.  (In the future, a spline will
                     be fit to the points if they number greater than
                     three.) Parameters are available to set color,
                     weight, and style.

           text      The text primitive draws characters.  It requires
                     a single point which locates the center of the
                     first character to be drawn.  Parameters are
                     color, font, textsize, and textangle.

           hardware  The hardware primitive draws hardware characters
                     or gives control commands to a hardware device.  A
                     single point locates the beginning location of the
                     hardware string.

           comment   A comment is an integer string that is included in
                     a GPS file but causes nothing to be displayed.
                     All GPS files begin with a comment of zero length.

         GPS PARAMETERS
           color     Color is an integer value set for arc, lines, and
                     text primitives.




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           weight    Weight is an integer value set for arc and lines
                     primitives to indicate line thickness.  The value
                     0 is  narrow weight, 1 is bold, and 2 is medium
                     weight.

           style     Style is an integer value set for lines and arc
                     primitives to give one of the five different line
                     styles that can be drawn on TEKTRONIX 4010 series
                     storage tubes.  They are:
                          0     solid
                          1     dotted
                          2     dot dashed
                          3     dashed
                          4     long dashed

           font      An integer value set for text primitives to
                     designate the text font to be used in drawing a
                     character string.  (Currently font is expressed as
                     a four-bit weight value followed by a four-bit
                     style value.)

           textsize  Textsize is an integer value used in text
                     primitives to express the size of the characters
                     to be drawn.  Textsize represents the height of
                     characters in absolute universe-units and is
                     stored at one-fifth this value in the size-
                     orientation (so) word (see below).

           textangle Textangle is a signed integer value used in text
                     primitives to express rotation of the character
                     string around the beginning point.  Textangle is
                     expressed in degrees from the positive x-axis and
                     can be a positive or negative value.  It is stored
                     in the size-orientation (so) word as a value
                     256/360 of it's absolute value.

         ORGANIZATION
           GPS primitives are organized internally as follows:

           lines          cw  points  sw
           arc       cw  points  sw
           text      cw  point  sw  so  [string]
           hardware       cw  point  [string]
           comment        cw  [string]

           cw        Cw is the control word and begins all primitives.
                     It consists of four bits that contain a
                     primitive-type code and twelve bits that contain
                     the word-count for that primitive.

           point(s)  Point(s) is one or more pairs of integer
                     coordinates.  Text and hardware primitives only



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                     require a single point.  Point(s) are values
                     within a cartesian plane or universe having 64K
                     (-32K to +32K) points on each axis.

           sw        Sw is the style-word and is used in lines, arc,
                     and text primitives.  For all three, eight bits
                     contain color information.  In arc and lines,
                     eight bits are divided as four bits weight and
                     four bits style.  In the text primitive, eight
                     bits of sw contain the font.

           so        So is the size-orientation word used in text
                     primitives.  Eight bits contain text size and
                     eight bits contain text rotation.

           string    String is a null-terminated character string.  If
                     the string does not end on a word boundary, an
                     additional null is added to the GPS file to insure
                     word-boundary alignment.

      SEE ALSO
           graphics(1), stat(1), toc(1) in the ROS Reference Manual.

































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