; $Id: dist.pro,v 1.14 2004/01/21 15:54:52 scottm Exp $ ; ; Copyright (c) 1982-2004, Research Systems, Inc. All rights reserved. ; Unauthorized reproduction prohibited. ; ;+ ; NAME: ; DIST ; ; PURPOSE: ; Create a rectangular array in which each element is proportional ; to its frequency. This array may be used for a variety ; of purposes, including frequency-domain filtering and ; making pretty pictures. ; ; CATEGORY: ; Signal Processing. ; ; CALLING SEQUENCE: ; Result = DIST(N [, M]) ; ; INPUTS: ; N = number of columns in result. ; M = number of rows in result. If omitted, N is used to return ; a square array. ; ; OUTPUTS: ; Returns an (N,M) floating array in which: ; ; R(i,j) = SQRT(F(i)^2 + G(j)^2) where: ; F(i) = i IF 0 <= i <= n/2 ; = n-i IF i > n/2 ; G(i) = i IF 0 <= i <= m/2 ; = m-i IF i > m/2 ; ; SIDE EFFECTS: ; None. ; ; RESTRICTIONS: ; None. ; ; PROCEDURE: ; Straightforward. The computation is done a row at a time. ; ; MODIFICATION HISTORY: ; Very Old. ; SMR, March 27, 1991 - Added the NOZERO keyword to increase efficiency. ; (Recomended by Wayne Landsman) ; DMS, July, 1992. - Added M parameter to make non-square arrays. ; CT, RSI, March 2000: Changed i^2 to i^2. to avoid overflow. ;- function dist,n,m ;Return a rectangular array in which each pixel = euclidian ;distance from the origin. compile_opt idl2 on_error,2 ;Return to caller if an error occurs n1 = n[0] m1 = (n_elements(m) le 0) ? n1 : m[0] x=findgen(n1) ;Make a row x = (x < (n1-x)) ^ 2 ;column squares a = FLTARR(n1,m1,/NOZERO) ;Make array for i=0L, m1/2 do begin ;Row loop y = sqrt(x + i^2.) ;Euclidian distance a[0,i] = y ;Insert the row if i ne 0 then a[0, m1-i] = y ;Symmetrical endfor return,a end