Dist function details

1. The Dist function algorithm is as follows (obviously, the essence of this algorithm is the commonly known Euclidean Distance Algorithm)

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

Illustration: tvscl, dist (200)

Extended: surface, dist (20),/save

IDL implementation source code:

; $Id: //depot/Release/ENVI51_IDL83/idl/idldir/lib/dist.pro#1 $;; Copyright (c) 1982-2013, Exelis Visual Information Solutions, Inc. All;       rights reserved. Unauthorized reproduction is 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 idl2on_error,2              ;Return to caller if an error occursn1 = n[0]m1 = (n_elements(m) le 0) ? n1 : m[0]x=findgen(n1)        ;Make a rowx = (x < (n1-x)) ^ 2    ;column squaresa = FLTARR(n1,m1,/NOZERO)    ;Make arrayfor 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 ;Symmetricalendforreturn,aend

2. Usage:

Dist (20, 20) generates an array of 20 × 20. When you enter dist (20), both the row and column are 20 by default.

3. Explanation of IDL help:

Dist

The Dist function creates an array in which each array element value is proportional to its frequency. This array may be used for a variety of purposes, including frequency-domain filtering.

This routine is written in the IDL Language. Its source code can be found in the file Dist. Pro In the Lib subdirectory of The IDL distribution.

Examples

; Display the results of DIST as an image:
Tvscl, dist (100)

Syntax

Result = dist (N [, m])

Return Value

Returns a rectangular array in which the value of each element is proportional to its frequency.

Argumentsn

The number of columns in the resulting array.

M

The number of rows in the resulting array. If M is omitted, the resulting array will be n by N.

Keywords

None.

 

 

 

Dist function details