Language Reference

GPIEXY Call

converts from polar to world coordinates

CALL GPIEXY( , , fract-radii, angles<, center<, radius<, window>);

The inputs to the GPIEXY subroutine are as follows:

and

are vectors of coordinates returned by GPIEXY.

fract-radii

is a vector of fractions of the radius of the reference circle.

angles

is the vector of angle coordinates in degrees.

center

defines the reference circle.

radius

defines the reference circle.

window

is a numeric matrix or literal specifying a window. This is given in world coordinates and has the form

{minimum-x minimum-y maximum-x maximum-y}

The GPIEXY subroutine computes the world coordinates of a sequence of points relative to a circle. The and arguments are vectors of new coordinates returned by the GPIEXY subroutine. Together, the vectors fract-radii and angles define the points in polar coordinates. Each pair from the fract-radii and angles vectors yields a corresponding pair in the and vectors. For example, suppose fract-radii has two elements, 0.5 and 0.3, and the corresponding two elements of angles are 90 and 30. The GPIEXY subroutine returns two elements in the vector and two elements in the vector. The first pair locates a point halfway from the center to the reference circle on the vertical line through the center, and the second pair locates a point one-third of the way on the line segment from the center to the reference circle, where the line segment slants 30 degrees from the horizontal. The reference circle can be defined by an earlier GPIE call or another GPIEXY call, or it can be defined by specifying center and radius.

Graphics devices can have diverse aspect ratios; thus, a circle can appear distorted when drawn on some devices. The IML graphics subsystem adjusts computations to compensate for this distortion. Thus, for any given point, the transformation from polar coordinates to world coordinates might need an equivalent adjustment. The GPIEXY subroutine ensures that the same adjustment applied in the GPIE subroutine is applied to the conversion. An example that uses the GPIEXY call follows:

  
       /* add labels to a pie with 4 slices of equal size */ 
    call gpie(50,50,30,{0 90 180 270},{90 180 270 0}); 
    call gpiexy(x,y,1.2,{45 135 225 315},{50 50},30,{0 0 100 100}); 
  
       /* adjust for label size: */ 
    x [4,]=x[4,]-3; 
    x [1,]=x[1,]-4; 
    x [2,]=x[2,]+1; 
    call gscript(x,y,{'QTR1' 'QTR2' 'QTR3' 'QTR4'}); 
    call gshow;