;======================================================================
; ESMF_wgts_13.ncl
;
; Concepts illustrated:
;   - Interpolating from one grid to another using ESMF_regrid_with_weights
;   - Interpolating from one grid to another using an existing weights file
;   - Interpolating data from an EASE grid to a 0.25 degree grid
;======================================================================
; This example is identical to ESMF_regrid_13.ncl, except it assumes
; the weights file already exists, and does regridding using 
; "ESMF_regrid_with_weights".  This is the best method to use if you 
; already have the weights.
;======================================================================
; This example uses the ESMF application "ESMF_RegridWeightGen" to 
; generate the weights.
;
; For more information about ESMF:
;
;        http://www.earthsystemmodeling.org/
;======================================================================
;
; These files are loaded by default in NCL V6.2.0 and newer
; load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
; load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
; load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
;
; This file still has to be loaded manually
load "$NCARG_ROOT/lib/ncarg/nclscripts/esmf/ESMF_regridding.ncl"

begin
    ease_file = addfile("EASE.nc","r")
    lat2d     = ease_file->latitude
    lon2d     = ease_file->longitude

;---Get date of interest: we will just regrid one time step.
    yyyymm    = 200502
    date      = ease_file->date
    nt        = ind(date.eq.yyyymm)          
    swe2d     = ease_file->SWE(nt,:,:)

    swe_regrid = ESMF_regrid_with_weights(swe2d,"EASE_2_NH_patch.nc",False)
    printVarSummary(swe_regrid)

;----------------------------------------------------------------------
; Plotting section
;----------------------------------------------------------------------
    wks = gsn_open_wks("png","ESMF_wgts")       ; send graphics to PNG file

    res                     = True              ; Plot mods desired.
    res@gsnMaximize         = True              ; Maximize plot

    res@gsnDraw             = False
    res@gsnFrame            = False

    res@cnFillOn            = True              ; color plot desired
    res@cnFillPalette       = "amwg"            ; set color map
    res@cnLinesOn           = False             ; turn off contour lines
    res@cnLineLabelsOn      = False             ; turn off contour labels
    res@cnFillMode          = "RasterFill"      ; turn raster on       

    res@cnLevelSelectionMode= "ExplicitLevels" ; set explicit contour levels
    res@cnLevels            = (/-300,-250,-200,-150,-100,   \
                                0,1,5,10,25,100,200,300,400/)

    res@lbLabelBarOn        = False              ; turn on in panel

    res@trGridType          = "TriangularMesh"   ; allow missing coordinates


    res@gsnPolar            = "NH"               ; specify the hemisphere
    res@mpMinLatF           = 35

;---Plot original data.
    res@gsnAddCyclic = False
    res@sfXArray     = lon2d
    res@sfYArray     = lat2d
    res@tiMainString = "Original EASE grid (" + str_join(dimsizes(lat2d),",") + ")"

    plot_orig   = gsn_csm_contour_map_polar(wks,swe2d,res)     

    delete(res@sfXArray)
    delete(res@sfYArray)

;---Plot regridded data.
    res@gsnAddCyclic = True

    dims = tostring(dimsizes(swe_regrid))
    res@tiMainString = "Regridded to 0.25 degree grid (" + \
                       str_join(dims," x ") + ")"

    plot_regrid = gsn_csm_contour_map_polar(wks,swe_regrid,res)     

;---Compare the plots in a panel
    pres                    = True
    pres@gsnMaximize        = True
    pres@gsnPanelLabelBar   = True
    pres@lbLabelFontHeightF = 0.01
    pres@pmLabelBarWidthF   = 0.8

    gsn_panel(wks,(/plot_orig,plot_regrid/),(/1,2/),pres)
end