pro getarc,im,orc,onum,awid,arc,pix \$ ,x_left_lim=x_left_lim,x_right_lim=x_right_lim ; This subroutine extracts a curved arc (arc) from an image array (im). The ; curvature of the arc is determined from polynomial fit coefficients (orc) ; which usually trace the curvature of the echelle orders. The particular ; arc to extract is specified by an order number (onum), which need not be ; integral. Positions of nonintegral orders are interpolated from surrounding ; orders. ; im (input array (# columns , # rows)) image from which to extract arc. ; orc (input array (# of coeff per fit , # of orders)) coefficients from PIT ; fit of column number versus row number (of echelle orders, usually). The ; polynomials trace arcs (orders, usually) indexed by order number, begining ; with zero closest to row zero and increasing as row number increases. ; **Note** These are the extended order coefficients. ; onum (input scalar) order number of arc to extract - need not be integral. ; awid (input scalar) full width of arc to be extracted. ; Two specifications are possible: ; max(awid) <= 1, awid is fraction of the local distance between orders to mash. ; max(awid) > 1, awid is the specific number of pixels to mash. ; arc (output vector (# columns)) counts PER PIXEL in arc extracted from image. ; [pix (output vector (# columns)] returns the fractional number of pixels ; mashed in each column to make arc. ;29-Nov-91 GB translated from ANA ;22-Dec-91 GB made to return zeros if arc off image ;05-Jul-94 JAV, CMJ Moved endelse to extract full arc instead of half when ; fraction of an arc is specified if n_params() lt 5 then begin print,'syntax: getarc,im,orc,onum,awid,arc[,pix]' retall endif if min(awid) le 0 then message,'GETARC: Arc width must be positive - aborting.' ncol=n_elements(im(*,0)) if(keyword_set(x_left_lim )) then i1 = x_left_lim else i1 = 0 if(keyword_set(x_right_lim)) then i2 = x_right_lim else i2 = ncol-1 ; i1 = 0 ; i2 = ncol-1 ;Define useful quantities ncol=n_elements(im(i1:i2,0)) ;number of columns nrow=n_elements(im(i1,*)) ;number of rows maxo=n_elements(orc(0,*))-1 ;maximum order covered by orc ix=findgen(ncol)+i1 ;vector of column indicies arc=ix*0.0 ;dimension arc vector pix=1.0 ;define in case of trouble ;Interpolate polynomial coefficients for surrounding orders to get polynomial ; coefficients. Note that this is mathematically equivalent to interpolating ; the column indicies for surrounding orders, since the column indicies are ; linear functions of the polynomial coefficients. However, interpolating ; coefficients should be faster. ;The +/- 10000 is to force argument of LONG to be positive before truncation. if max(awid) le 1 then begin ;awid is an order fraction if onum lt awid or onum gt maxo-awid then begin ;onum must be covered by orc message,'Requested order not covered by order location coefficients.' \$ + strtrim(onum,2) endif ob=onum-awid/2.0 ;order # of bottom edge of arc obi=long(ob+10000)-10000 ;next lowest integral order #A cb=orc(*,obi)+(ob-obi)*(orc(*,obi+1)-orc(*,obi)) yb=poly(ix,cb) ;row # of bottom edge of swath ybi=long(yb+10000)-10000 ;lowest pixel number in swath ybfrac=yb-ybi ;fraction of ybi to exclude if min(yb) lt 0 then begin ;check if arc is off bottom print,'GETARC: Warning - requested arc is below bottom of image.' \$ + strtrim(onum,2) return endif ot=onum+awid/2.0 ;order # of top edge of arc oti=long(ot+10000)-10000 ;next lowest integral order # ct=orc(*,oti)+(ot-oti)*(orc(*,oti+1)-orc(*,oti)) yt=poly(ix,ct) ;row # of top edge of swath yti=long(yt+10001)-10000 ;highest pixel number in swath ytfrac=yti-yt ;fraction of yti to exclude if max(yt) gt nrow-1 then begin ;check if arc is off top of im print,'FORDS: Warning - requested arc is above top of image.' \$ + strtrim(onum,2) return endif endif else begin ;awid is number of pixels if onum lt 0 or onum gt maxo then begin ;onum must be covered by orc message,'Requested order not covered by order location coefficients.' \$ + strtrim(onum,2) endif ob=onum ;order # of middle of arc obi=long(ob+10000)-10000 ;next lowest integral order # cb=orc(*,obi)+(ob-obi)*(orc(*,obi+1)-orc(*,obi)) yb=poly(ix,cb)-awid/2.0 ;row # of bottom edge of swath ybi=long(yb+10000)-10000 ;lowest pixel number in swath ybfrac=yb-ybi ;fraction of ybi to exclude if min(yb) lt 0 then begin ;check if arc is off bottom print,'FORDS: Warning - requested arc is below bottom of image.' \$ + strtrim(onum,2) return endif ot=onum ;order # of middle of arc oti=long(ot+10000)-10000 ;next lowest integral order # ct=orc(*,oti)+(ot-oti)*(orc(*,oti+1)-orc(*,oti)) yt=poly(ix,ct)+awid/2.0 ;row # of top edge of swath yti=long(yt+10001)-10000 ;highest pixel number in swath ytfrac=yti-yt ;fraction of yti to exclude if max(yt) gt nrow-1 then begin ;check if arc is off top of im print,'FORDS: Warning - requested arc is above top of image.' \$ + strtrim(onum,2) return endif endelse diff = round(mean(yti - ybi)*0.5) yb = round((ybi + yti)*0.5-diff)>0 yt = round((ybi + yti)*0.5+diff)<(nrow-1) for col=0,ncol-1 do begin ;sum image in requested arc scol=im(col+i1,yb(col):yt(col)) arc(col)=total(scol) end ; faster method for summing arc ; irow=indgen(nrow) ; for row=min(ybi),max(yti) do begin ;loop through valid rows ; srow=im(*,row) ;get CCD row ; mask=srow*0. ;make a mask for it ; madd=where(row ge ybi and row le yti) ;choose pixels in this row ; mask(madd)=1. ;that belong in this order ; arc=arc+srow*mask ;add them into extracted spectr ; endfor ;Define vectors along edge of swath. vb =float(im(ix+ncol*ybi)) ;bottommost pixels in swath vt =float(im(ix+ncol*yti)) ;topmost pixels in swath ;Now subtract out extra pixels at the top and bottom of the swath. ; arc = arc - 0.5 * (vb+vt) \$ ; - (vb + 0.5*(im(ix+ncol*(ybi+1))-vb)*ybfrac)*ybfrac \$ ; - (vt - 0.5*(vt-im(ix+ncol*(yti-1)))*ytfrac)*ytfrac ; pix = yt - yb ;number of pixels mashed in arc ; arc = arc / pix ;convert to counts/pixel return end