Pro Tvcross, length, xc, yc, color, COLOR = TheColor, THICK = thick
;+
; NAME:
;    TVCross
; PURPOSE:
;    To draw a circle of specified radius centered on the cursor, or at
;    specified position
; CALLING SEQUENCE:
;    TVcross, length, x, y, color, [ COLOR = , THICK = ]         
; INPUTS:
;    length - length of cross to be drawn, scalar
; OPTIONAL INPUT:
;    X - x position for circle center, vector or scalar
;    Y - y position for circle center, vector or scalar
;        If X and Y are not specified then program will draw circle at
;        at the current cursor position
;    COLOR - intensity value (0-255) used to draw the circle, Default =
;        !P.COLOR.   User can specify color using either this parameter or the
;        COLOR keyword.  
; OPTIONAL KEYWORD INPUTS:
;    THICK - thickness of the drawn circle,  default = !P.THICK (=1)
;    COLOR - Intensity value used to draw the circle.  Default = !P.COLOR
; OUTPUTS:
;    None
;-

   On_Error, 2   ; Return to caller

   if N_params() LT 1 then begin
         print,'Syntax - tvcross, length, [ xc, yc, color, COLOR = ,THICK = ]'
         return
   endif

   if N_elements(length) NE 1 then message, $
          'ERROR - Cross length (first parameter) must be a scalar'


   if not keyword_set(TheColor) then begin
      IF N_Elements( Color ) eq 0 THEN Color = !P.COLOR
   endif else color = TheColor

   if not keyword_set(THICK) then thick = !P.THICK


   x = findgen(2*length)
   x=x*0.0
   y = findgen(2*length) - length

   

   oPlot, x + xc, y+ yc , COLOR = Color, THICK = thick

   x = findgen(2*length) - length
   y = findgen(2*length)
   y = y*0.0

   

;   oPlot, x + xc, y+ yc , COLOR = Color, /DEV, THICK = thick
   oPlot, x + xc, y+ yc , COLOR = Color, THICK = thick

   Return

End; TVcross