pro add_distort, hdr, astr; NAME:;    ADD_DISTORT; PURPOSE:;    Add the distortion parameters in an astrometry structure to a FITS header.; EXPLANATION:;    PUTAST currently does not add the SIP (Spitzer Imaging Polynomial) ;    distortion parameters when writing an astrometry structure to a FITS ;    header.    Therefore, to include the distortion polynomial, one should;    call add_distort after putast. ;;    IDL> putast,h ,astr0;    IDL> add_distort,h,astr0;; CALLING SEQUENCE:;     add_distort, hdr, astr    ;; INPUTS:;     HDR -  FITS header, string array.   HDR will be updated to contain;             the supplied astrometry.;     ASTR - IDL structure containing values of the astrometry parameters;            CDELT, CRPIX, CRVAL, CTYPE, LONGPOLE, PV2 and DISTORT;            See EXTAST.PRO for more info about the structure definition;; PROCEDURES USED:;       SXADDPAR, TAG_EXIST(); REVISION HISTORY:;       Written by W. Landsman  May 2005;- npar = N_params() if ( npar LT 2 ) then begin    ;Was header supplied?        print,'Syntax: ADD_DISTORT, Hdr, astr'        return endif  add_distort = tag_exist(astr,'distort')  if add_distort then begin   sxaddpar,hdr,'CTYPE1','RA---TAN-SIP'    sxaddpar,hdr,'CTYPE2','DEC--TAN-SIP'     distort = astr.distort     a_dimen = size(distort.a,/dimen)      b_dimen = size(distort.b,/dimen)     ap_dimen = size(distort.ap,/dimen)      bp_dimen = size(distort.bp,/dimen)  if a_dimen[0] GT 0 then begin        a_order = a_dimen[0]-1         sxaddpar, hdr, 'A_ORDER', a_order, /savec, $                  'polynomial order, axis 1, detector to sky '        for i=0, a_order do begin            for j = 0, a_order do begin             aij = distort.a[i,j]             if aij NE 0.0 then $                sxaddpar, hdr, 'A_' + strtrim(i,2)+ '_' + strtrim(j,2), aij, $                ' distortion coefficient', /savec             endfor         endfor  endif  if b_dimen[0] GT 0 then begin        b_order = b_dimen[0]-1         sxaddpar, hdr, 'B_ORDER', a_order, /savec , $                  'polynomial order, axis 2, detector to sky'        for i=0, b_order do begin            for j = 0, b_order do begin             bij = distort.b[i,j]             if bij NE 0.0 then $                sxaddpar, hdr, 'B_' + strtrim(i,2)+ '_' + strtrim(j,2), bij, $                ' distortion coefficient', /savec             endfor         endfor  endif  if ap_dimen[0] GT 0 then begin        ap_order = ap_dimen[0]-1         sxaddpar, hdr, 'AP_ORDER', a_order, /savec, $                  ' polynomial order, axis 1, sky to detector '        for i=0, ap_order do begin            for j = 0, ap_order do begin             apij = distort.ap[i,j]             if apij NE 0.0 then $                sxaddpar, hdr, 'AP_' + strtrim(i,2)+ '_' + strtrim(j,2), apij, $                ' distortion coefficient', /savec             endfor         endfor  endif  if bp_dimen[0] GT 0 then begin        bp_order = bp_dimen[0]-1         sxaddpar, hdr, 'BP_ORDER', a_order, /savec, $                  ' polynomial order, axis 2, sky to detector '        for i=0, bp_order do begin            for j = 0, bp_order do begin             bpij = distort.bp[i,j]             if bpij NE 0.0 then $                sxaddpar, hdr, 'BP_' + strtrim(i,2)+ '_' + strtrim(j,2), bpij, $                ' distortion coefficient', /savec             endfor         endfor  endif endif return end