idlastro / Miscellaneous (Non-Astronomy) Procedures: ONE_RAY

[Source code]

NAME
ONE_RAY
PURPOSE
Draw a line with a specified starting point, length, and  angle
CALLING SEQUENCE
one_ray, xcen, ycen, len, angle, terminus, /NODRAW ]
INPUT PARAMETERS
xcen, ycen = starting point in device coordinates, floating point 
                scalars
len        = length in pixels, device coordinates
angle      = angle in degrees counterclockwise from +X direction
OUTPUT PARAMETERS
terminus = two-element vector giving ending point of ray in device
        coordinates
OPTIONAL KEYWORD INPUT PARAMETERS
/nodraw   if non-zero, the ray is not actually drawn, but the terminus
        is still calculated
 Any valid keyword to cgPLOTS can also be passed ot ONE_RAY.   In
 particular, COLOR, THICK, and LINESTYLE control the color, thickness
 and linestyle of the drawn line.
EXAMPLE
Draw a double thickness line of length 32 pixels from (256,256) 
45 degrees counterclockwise from the X axis
IDL> one_ray, 256, 256, 32, 45 ,term, THICK = 2
PROCEDURE straightforward matrix arithmetic
MODIFICATION HISTORY
Written by R. S. Hill, Hughes STX Corp., 20-May-1992.
Modified to work correctly for COLOR=0  J.Wm.Parker  HITC   1995 May 25
Added _EXTRA keywords to PLOT   W. Landsman   November 2006
Work with Coyote Graphcis W. Landsman February 2011