Previous: pl2mc Up: ../plot79_p.html Next: pl2sp

PL2PO

       SUBROUTINE  PL2PO (PH,R,VISBLE)
 C$    (2-D Plane Polar Pen Movement)
 C$    Change  the  angular  variables  (PH,R)  to  the  Cartesian
 C$    coordinates (X,Y) so as to  define directly in plane  polar
 C$    coordinates points which  lie upon the  surface of the  X-Y
 C$    plane.  R  is assumed  to be  scaled to  the unit  interval
 C$    0..1, but for  convenience PH  is permitted to  lie in  the
 C$    range -1..+1, since this frequently happens when angles are
 C$    computed with the ATAN2 function.  In addition, the angular
 C$    interval is adjusted to encompass  no more than 0.5  units,
 C$    since this proves to be  necessary for the hidden-line  and
 C$    contour routines.
 C$
 C$    The Cartesian coordinates  (X,Y) are adjusted  to the  unit
 C$    interval and passed  to MOVA2/LINA2 as  (X,Y), so that  the
 C$    default view plane (the X-Y plane) will receive the  image.
 C$    The polar coordinate ranges are:
 C$
 C$    0 .LE. PHI .LE. 2*pi
 C$    0 .LE. RHO .LE. +infinity
 C$
 C$    See H. Margenau  and G.M. Murphy,  "Mathematics of  Physics
 C$    and Chemistry", 2nd  Ed., Van  Nostrand (1956),  Vol 1,  p.
 C$    178.  These are related to the Cartesian coordinates by:
 C$
 C$    X = RHO*COS(PHI)
 C$    Y = RHO*SIN(PHI)
 C$
 C$    The coordinate surfaces are
 C$    (1) concentric circles about the origin (RHO = constant)
 C$    (2) radial lines from the origin (PHI = constant).
 C$
 C$    To  obtain  coordinates  (PH,R)   expressed  on  the   unit
 C$    interval, (PHI,RHO) are transformed as follows:
 C$
 C$    PH = PHI/TWOPI
 C$    R = RHO   (simply clipped to 0..1)
 C$    (09-APR-82)