;+
;
; @file_comments
; Rotate two vectors by a specified amount.
;
; @param X {in}{required}
; original data point pairs
;
; @param Y {in}{required}
; original data point pairs
;
; @param DEG {in}{required}
; degrees to rotate.
;
; @param NX {out}
; rotated point pairs.
;
; @param NY {out}
; rotated point pairs.

; @history
; Jeff Bennett, U of Colorado
;
; @version
; $Id$
;
;-
PRO rotation,X,Y,DEG,NX,NY
;
  compile_opt idl2, strictarrsubs
;
ang=deg*!dtor

;convert to polar coordinates for rotation
r = sqrt(x*x + y*y)
theta = r*0.
;get angle in for loop so that zero radii will be left as zero angle
for i = 0,n_elements(r)-1 do $
if r[i] ne 0 then theta[i] = atan(y[i],x[i])  ;range from -pi to +pi
;
;add rotation angle
theta = theta + ang
;
;convert back to rectangular coordinates, now rotated
nx = r * cos(theta)
ny = r * sin(theta)
;
return
end