;-----------------------------------------------------------------------
; Savitzky-Golay Smoothing Filter
; Input: hyperspectral file, SG parameters(Nleft, Nright, Order, Degree)
; Output: smoothed hrs file.
; created by Shuai Tong 2012.8
;-----------------------------------------------------------------------

PRO SGFilter, Nleft, Nright, Order, Degree 
  
  ; REFERENCE: HELP about SAVGOL
  ; Specify the following parameters!!! 
  Nleft=5   ; lt nb/2 ?
  Nright=5  ; lt nb/2 ?
  Order=0
  Degree=3 
        
  ;OPEN FILE
  file = DIALOG_PICKFILE(/READ, FILTER = '*.img') 
  print,file
  ENVI_OPEN_FILE, file, r_fid=fid 
  ENVI_FILE_QUERY, fid, dims=dims, ns=ns, nl=nl, nb=nb 
  
  ; READ DATA
  fdata = fltarr(ns,nl,nb)
  for i=0,nb-1 do begin
    fdata[*,*,i] = ENVI_GET_DATA(fid=fid, dims=dims, pos=i)
  endfor
  
  ; Savitzky-Golay with XX, Nth degree polynomial: 
  savgolFilter = SAVGOL(Nleft, Nright, Order, Degree)
  SGdata = CONVOL(transpose(fdata), savgolFilter, /EDGE_TRUNCATE)
  SGdata = transpose(SGdata)
  
  ; output
  OutName = file_basename(file,'.img')+'_SG.img'
  ENVI_WRITE_ENVI_FILE, SGdata, out_name=OutName

END