FUNCTION ToRadians, degrees=Degrees

;+
; NAME:
;	ToRadians
; PURPOSE:
;	Get conversion factor needed to convert angles to radians,
;	depending on setting of keyword Degrees
; CATEGORY:
;	Number strangling
; CALLING SEQUENCE:
;	radians_per_mystery_unit = ToRadians(degrees=Degrees)
; OPTIONAL INPUT PARAMETERS:
;	/degrees			indicates whether input angles are in
;						radians (not set) or degrees (set)
; OUTPUTS:
;	radians_per_mystery_unit
;				= 1.0        if Degrees not set
;				= 1.0/!radeg if Degrees set
;						Results is double precision
; INCLUDE:
	@compile_opt.pro	; On error, return to caller
; SEE ALSO:
;	ToDegrees
; PROCEDURE:
;	Many procedures which process angles allow the keyword /Degrees
;	to indicate that the input and/or output angles are in degrees,
;	rather than the default radians. This function returns the
;	conversion factor required to convert to radians. Usually
;	this function is used at the beginning of the procedure to convert
;	all angles from the input units to radians, and at the end to convert
;	back from radians to the input units.
; MODIFICATION HISTORY:
;	JAN-1998, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
;-

D = keyword_set(Degrees)
RETURN, D*!dpi/180.d0+(1-D)*1.0d0  &  END