PGPLOT Module: PGPT1 -- draw one graph marker

SUBROUTINE PGPT1 (XPT, YPT, SYMBOL)
REAL XPT, YPT
INTEGER SYMBOL

Primitive routine to draw a single Graph Marker at a specified point.
The marker is drawn using the current values of attributes
color-index, line-width, and character-height (character-font applies
if the symbol number is >31). If the point to be marked lies outside
the window, no marker is drawn. The "pen position" is changed to
(XPT,YPT) in world coordinates.

To draw several markers with coordinates specified by X and Y
arrays, use routine PGPT.

Arguments
XPT (input) : world x-coordinate of the point.
YPT (input) : world y-coordinate of the point.
SYMBOL (input) : code number of the symbol to be drawn:
-1, -2 : a single dot (diameter = current
line width).
-3..-31 : a regular polygon with ABS(SYMBOL)
edges (style set by current fill style).
0..31 : standard marker symbols.
32..127 : ASCII characters (in current font).
e.g. to use letter F as a marker, let
SYMBOL = ICHAR('F').
> 127 : a Hershey symbol number.