GPS(4)                               SysV                               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(1G)) 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.

     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 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(1G), stat(1G), in the SysV Command Reference.