;======================================================================
; ESMF_wgts_10.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 MPAS grid to 0.25 degree grid
;======================================================================
; This example is identical to ESMF_regrid_10.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
;---Retrieve data to regrid
    sfile = addfile("MPAS.nc","r")
    sp    = sfile->surface_pressure(0,:)
    sp    = sp/1000.   ; Not sure what the pressure units are, there's
                       ; not much metadata info on this file

    r2d     = 180.0d/(atan(1)*4.0d)  ; Radian to Degree
    lonCell = sfile->lonCell         ; Cell centers, for plotting later
    latCell = sfile->latCell
    lonCell = lonCell*r2d
    latCell = latCell*r2d

;---Do the regridding using an existing weights file
    sp_regrid = ESMF_regrid_with_weights(sp,"MPAS_2_World.nc",False)
    printVarSummary(sp_regrid)

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

;---Resources to share between both plots
    res                     = True              ; Plot modes desired.

    res@gsnDraw             = False
    res@gsnFrame            = False

    res@gsnMaximize         = True              ; Maximize plot

    res@cnFillOn            = True              ; color plot desired
    res@cnFillPalette       = "rainbow"         ; 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 = "ManualLevels"
    res@cnMinLevelValF       =  55
    res@cnMaxLevelValF       = 100
    res@cnLevelSpacingF      =   2.5

    res@lbLabelBarOn        = False    ; Will turn on in panel later.

    res@mpFillOn            = False

    res@trGridType         = "TriangularMesh"  ; allow missing coordinates
    res@gsnAddCyclic       = False

;---Resources for plotting regridded data
    res@gsnAddCyclic       = False

    dims = tostring(dimsizes(sp_regrid))
    res@tiMainString          = "Data regridded to 0.25 degree grid (" + \
                                str_join(dims," x ") + ")"

    plot_regrid = gsn_csm_contour_map(wks,sp_regrid,res)

    res@sfXArray           = lonCell
    res@sfYArray           = latCell
    res@gsnAddCyclic       = False

    res@tiMainString       = "Original MPAS grid (" + dimsizes(sp) + " cells)"

    plot_orig = gsn_csm_contour_map(wks,sp,res)  

;---Compare the plots in a panel
    pres                   = True
    pres@gsnMaximize       = True
    pres@gsnPanelLabelBar  = True

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