PRO GROUP, X, Y, RCRIT, NGROUP ;+ ; NAME: ; GROUP ; PURPOSE: ; Assign stars with non-overlapping PSF profiles into distinct groups ; EXPLANATION: ; Part of the IDL-DAOPHOT sequence ; ; CALLING SEQUENCE: ; GROUP, X, Y, RCRIT, NGROUP ; ; INPUTS: ; X - vector, giving X coordinates of a set of stars. ; Y - vector, giving Y coordinates of a set of stars. ; If X and Y are input as integers, then they will be converted to ; floating point ; RCRIT - scalar, giving minimum distance between stars of two ; distinct groups. Stars less than this distance from ; each other are always in the same group. Stetson suggests ; setting the critical distance equal to the PSF radius + ; the Fitting radius. ; ; OUTPUTS: ; NGROUP - integer vector, same number of elements as X and Y, ; giving a group number for each star position. Group ; numbering begins with 0. ; ; METHOD: ; Each position is initially given a unique group number. The distance ; of each star is computed against every other star. Those distances ; less than RCRIT are assigned the minimum group number of the set. A ; check is then made to see if any groups have merged together. ; ; PROCEDURES USED: ; REM_DUP() ; ; REVISION HISTORY: ; Written W. Landsman STX April, 1988 ; Major revision to properly merge groups together W. Landsman Sep 1991 ; Work for more than 32767 points W. Landsman March 1997 ; Converted to IDL V5.0 W. Landsman September 1997 ; Avoid overflow if X and Y are integers W. Landsman Feb. 1999 ;- On_error,2 ;Return to caller if N_params() LT 4 then begin print,'Syntax - group, x, y, rcrit, ngroup' print,' x,y - Input position vectors' print,' rcrit - Minimum radius between stars of different groups' print,' ngroup - Output vector of group indices' return endif rcrit2 = rcrit^2 ;Don't bother taking square roots npts = min( [N_elements(x), N_elements(y)] ) ;Number of stars if npts LT 2 then message, \$ 'ERROR - Input position X,Y vectors must contain at least 2 points' x = 1.0*x & y = 1.0*y ;Make sure at least floating point ngroup = lindgen(npts) ;Initially each star in a separate group ; Whenever the positions between two stars are less than the critical ; distance, assign both stars the minimum group id. The tricky part ; is to recognize when distinct groups have merged together. for i = 0l,npts-2 do begin dis2 = (x[i] - x[i+1:*])^2 + (y[i] - y[i+1:*])^2 good = where( dis2 LE rcrit2, ngood) if ngood GT 0 then begin ;Any stars within critical radius? good = [i,good+i+1] groupval = ngroup[good] mingroup = min( groupval ) if ( mingroup LT i ) then begin ;Any groups merge? groupval = groupval[ where( groupval LT i, nval) ] if nval GT 1 then \$ groupval = groupval[ rem_dup(groupval) ] nval = N_elements(groupval) if nval GE 2 then for j= 1, nval-1 do begin redo = where ( ngroup EQ groupval[j], ndo ) if ndo GT 0 then ngroup[redo] = mingroup endfor endif ngroup[good] = mingroup endif endfor ; ; Star are now placed in distinct groups, but they are not ordered ; consecutively. Remove gaps in group ordering ; if max(ngroup) EQ 0 then return ;All stars in one group ? ghist = histogram(ngroup,min=0) gmax = max(ghist) val = where(ghist GE 1, ngood) if ( ngood GT 0 ) then \$ for i = 0, ngood-1 do ngroup[ where( ngroup EQ val[i] ) ] = i message,'Number of Groups: '+ strtrim(ngood,2), /INF message,'Largest group size '+ strtrim(gmax,2) + ' stars',/INF return end