pro dist_circle ,im, n, xcen ,ycen, DOUBLE = double ;+ ; NAME: ; DIST_CIRCLE ; PURPOSE: ; Form a square array where each value is its distance to a given center. ; EXPLANATION: ; Returns a square array in which the value of each element is its ; distance to a specified center. Useful for circular aperture photometry. ; ; CALLING SEQUENCE: ; DIST_CIRCLE, IM, N, [ XCEN, YCEN, /DOUBLE ] ; ; INPUTS: ; N = either a scalar specifying the size of the N x N square output ; array, or a 2 element vector specifying the size of the ; N x M rectangular output array. ; ; OPTIONAL INPUTS: ; XCEN,YCEN = Scalars designating the X,Y pixel center. These need ; not be integers, and need not be located within the ; output image. If not supplied then the center of the output ; image is used (XCEN = YCEN = (N-1)/2.). ; ; OUTPUTS: ; IM - N by N (or M x N) floating array in which the value of each ; pixel is equal to its distance to XCEN,YCEN ; ; OPTIONAL INPUT KEYWORD: ; /DOUBLE - If this keyword is set and nonzero, the output array will ; be of type DOUBLE rather than floating point. ; ; EXAMPLE: ; Total the flux in a circular aperture within 3' of a specified RA ; and DEC on an 512 x 512 image IM, with a header H. ; ; IDL> adxy, H, RA, DEC, x, y ;Convert RA and DEC to X,Y ; IDL> getrot, H, rot, cdelt ;CDELT gives plate scale deg/pixel ; IDL> cdelt = cdelt*3600. ;Convert to arc sec/pixel ; IDL> dist_circle, circle, 512, x, y ;Create a distance circle image ; IDL> circle = circle*abs(cdelt[0]) ;Distances now given in arcseconds ; IDL> good = where(circle LT 180) ;Within 3 arc minutes ; IDL> print,total( IM[good] ) ;Total pixel values within 3' ; ; RESTRICTIONS: ; The speed of DIST_CIRCLE decreases and the the demands on virtual ; increase as the square of the output dimensions. Users should ; dimension the output array as small as possible, and re-use the ; array rather than re-calling DIST_CIRCLE ; ; MODIFICATION HISTORY: ; Adapted from DIST W. Landsman March 1991 ; Allow a rectangular output array W. Landsman June 1994 ; Converted to IDL V5.0 W. Landsman September 1997 ; Add /DOUBLE keyword, make XCEN,YCEN optional W. Landsman Jun 1998 ;- On_error,2 ;Return to caller if an error occurs if N_params() LT 2 then begin print,'Syntax - DIST_CIRCLE, im, n,[ xcen, ycen, /DOUBLE ]' print,'IM - output image array' print,'N - size of the output image array, scalar or 2 element vector' print,'XCEN,YCEN - position from which to specify distances' return endif if N_elements(N) EQ 2 then begin nx = n[0] ny = n[1] endif else if N_elements(N) EQ 1 then begin ny = n nx = n ;Make a row endif else message, \$ 'ERROR - Output size parameter N must contain 1 or 2 elements' if N_params() LT 4 then begin xcen = (nx-1)/2. & ycen = (ny-1)/2. endif if keyword_set(DOUBLE) then begin x_2 = (dindgen(nx) - xcen) ^ 2 ;X distances (squared) y_2 = (dindgen(ny) - ycen) ^ 2 ;Y distances (squared) im = dblarr( nx, ny, /NOZERO) ;Make uninitialized output array endif else begin x_2 = (findgen(nx) - xcen) ^ 2 ;X distances (squared) y_2 = (findgen(ny) - ycen) ^ 2 ;Y distances (squared) im = fltarr( nx, ny, /NOZERO) ;Make uninitialized output array endelse for i = 0L, ny-1 do begin ;Row loop im[0,i] = sqrt(x_2 + y_2[i]) ;Euclidian distance endfor return end