;----------------------------------------------------------------------
; ESMF_regrid_template.ncl
;
; This is a template file for use with ESMF regridding. This is the
; template that uses the single "ESMF_regrid" function to do the 
; regridding. There's another template, "ESMF_template.ncl", that
; does the regridding in several individual steps. This can be 
; useful if you need to skip any of the steps.
;
; The ESMF_regrid function does the following:
;
;   1. Generates a description file (SCRIP or ESMF) for the source grid.
;
;   2. Generates a description file (SCRIP or ESMF) for the destination
;      grid.
;
;   3. Generates the weights file, using the source and destination
;      files.
;
;   4. Applies the weights to the data you want to regrid.
;
;   5. Attaches metadata to regridded variable, if appropriate.
;
;----------------------------------------------------------------------
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_csm.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
load "$NCARG_ROOT/lib/ncarg/nclscripts/esmf/ESMF_regridding.ncl"

begin
;---Input file that contains lat/lon grid of source grid, and some data to regrid
    srcFileName = "test_in.nc"

;;;Details from ncl_filedump -c of test_in.nc:
;;; Copyright (C) 1995-2014 - All Rights Reserved
;;; University Corporation for Atmospheric Research
;;; NCAR Command Language Version 6.2.0
;;; The use of this software is governed by a License Agreement.
;;; See http://www.ncl.ucar.edu/ for more details.
;;;
;;;Variable: f
;;;Type: file
;;;filename:    test_in
;;;path:        test_in.nc
;;;   file global attributes:
;;;      creation_date : Thu Aug 14 12:12:20 GMT 2014
;;;      NCL_Version : 6.2.0
;;;      system : Linux metappdev.afccc.af.mil 2.6.32-431.20.3.el6.x86_64 #1 SMP Fri Jun 6 18:30:54 EDT 2014 x86_64 x86_64
 x86_64 GNU/Linux
;;;      Conventions : None
;;;      grib_source : prate.2014070800.ENSMEAN.ensmean.anom.1x1.grb
;;;      title : NCL: convert-GRIB-to-netCDF
;;;   dimensions:
;;;      forecast_time0 = 7
;;;      lat_3 = 181
;;;      lon_3 = 360
;;;   variables:
;;;      float PRATE_3_SFC_ave1m ( forecast_time0, lat_3, lon_3 )
;;;         initial_time :      07/08/2014 (00:00)
;;;         model :     Climate Data Assimilation System 2 (CDAS2)
;;;         parameter_number :  59
;;;         parameter_table_version :   2
;;;         grid_number :       3
;;;         level_indicator :   1
;;;         _FillValue :        1e+20
;;;         units :     kg/m^2/s
;;;         long_name : Precipitation rate
;;;         center :    US National Weather Service - NCEP (WMC)
;;;
;;;      float lat_3 ( lat_3 )
;;;         units :     degrees_north
;;;         grid_description :  65160-point (181x360) global longitude-latitude grid.  (0,0) at 0E, 90N, matrix layout.  N
.B.: prime meridian not duplicated.
;;;         long_name : latitude
;;;
;;;      float lon_3 ( lon_3 )
;;;         units :     degrees_east
;;;         grid_description :  65160-point (181x360) global longitude-latitude grid.  (0,0) at 0E, 90N, matrix layout.  N
.B.: prime meridian not duplicated.
;;;         long_name : longitude
;;;
;;;      integer forecast_time0 ( forecast_time0 )
;;;         units :     months
;;;         long_name : Forecast offset from initial time
;;;
;;;Coordinates:
;;; 
;;;     forecast_time0:
;;;  
;;;   2   3   4   5   6   7   8
;;;  
;;;     lat_3:
;;;  
;;;   90.00       89.00       88.00       87.00       86.00       85.00    
;;;   ...
;;;  -84.00      -85.00      -86.00      -87.00      -88.00      -89.00    
;;;  -90.00    
;;;  
;;;     lon_3:
;;;  
;;;   0.000       1.000       2.000       3.000       4.000       5.000    
;;;   ...
;;;   354.0       355.0       356.0       357.0       358.0       359.0    


;---Input file that contains lat/lon grid of destination grid, if applicable.
    dstFileName = "test_out.nc"

;;; NOTE:  test_out.nc is empty netcdf created from ncgen <CDL template>
;;;Details from ncl_filedump -c of test_out.nc:
;;; Copyright (C) 1995-2014 - All Rights Reserved
;;; University Corporation for Atmospheric Research
;;; NCAR Command Language Version 6.2.0
;;; The use of this software is governed by a License Agreement.
;;; See http://www.ncl.ucar.edu/ for more details.
;;;
;;;Variable: f
;;;Type: file
;;;filename:    test_out
;;;path:        test_out.nc
;;;   file global attributes:
;;;   dimensions:
;;;      fcst_time = 7
;;;      lat = 180
;;;      lon = 360
;;;   variables:
;;;      float lat ( lat )
;;;         units :     degrees_north
;;;         actual_range :      ( -89.5, 89.5 )
;;;         long_name : Latitude
;;;         standard_name :     latitude
;;;         axis :      Y
;;;         coordinate_defines :        point
;;;
;;;      float lon ( lon )
;;;         long_name : Longitude
;;;         units :     degrees_east
;;;         standard_name :     longitude
;;;         actual_range :      ( 0.5, 359.5 )
;;;         axis :      X
;;;         coordinate_defines :        point
;;;
;;;      float prate ( fcst_time, lat, lon )
;;;         initial_time :      07/08/2014 (00:00)
;;;         model :     Climate Data Assimilation System 2 (CDAS2)
;;;         parameter_number :  59
;;;         parameter_table_version :   2
;;;         grid_number :       3
;;;         level_indicator :   1
;;;         _FillValue :        1e+20
;;;         units :     kg/m^2/s
;;;         long_name : 1 month Avg Precipitation rate
;;;         center :    US National Weather Service - NCEP (WMC)
;;;
;;;      integer fcst_time ( fcst_time )
;;;         long_name : MonthsForecast offset from initial time
;;;         units :     months
;;;
;;;Coordinates:
;;; 
;;;     fcst_time:
;;;  
;;;   2   3   4   5   6   7   8
;;;  
;;;     lat:
;;;  
;;;   89.50       88.50       87.50       86.50       85.50       84.50    
;;;   ...
;;;  -84.50      -85.50      -86.50      -87.50      -88.50      -89.50    
;;;  
;;;     lon:
;;;  
;;;  0.5000       1.500       2.500       3.500       4.500       5.500    
;;;  ...
;;;   354.5       355.5       356.5       357.5       358.5       359.5    


;---Open the source data file and get some data to regrid
    sfile = addfile(srcFileName,"r")
    varname = "PRATE_3_SFC_ave1m"
    var     = sfile->$varname$           ; You may need to subscript this.

;---Open the destination data file
    dfile = addfile(dstFileName,"r")

;---Don't need to plot, need to write file, so open the output file
    outFileName = "regrid.nc"
    ofile = addfile(outFileName, "w")

;---Set up options for regridding
    Opt                = True

    Opt@SrcGridLat     = sfile->lat_3    ; Be sure to use appropriate names 
    Opt@SrcGridLon     = sfile->lon_3    ;here
    Opt@SrcRegional    = False         ; Necessary if source grid not global
    Opt@SrcTitle       = "NCEP Grid"   ; Optional 
;    Opt@SrcMask2D      = where(.not.ismissing(var),1,0) ; Necessary if has
                                                      ; missing values.

;
; If your destination grid is contained in a file, then use this code.
; Otherwise, if you just want to regrid to a generic grid, like a
; "1x1 degree grid, then skip to the next set of resources.
;
    dstlat             = dfile->lat    ; Be sure to use appropriate names 
    dstlon             = dfile->lon    ; here.
    Opt@DstGridLon     = dstlon
    Opt@DstGridLat     = dstlat
;    Opt@DstMask2D = where(.not.ismissing(dstlat).and.\
;                          .not.ismissing(dstlon),1,0) ; Necessary if lat/lon
                                                      ; has missing values.
;
; Use this if you just want to regrid to some generic grid, like a "1x
; "1x1 degree grid.
;
;;    Opt@DstGridType    = "1x1"

;    Opt@DstRegional    = False          ; Necessary if destination grid not global

    Opt@ForceOverwrite = True          ; Optional, but recommended
    Opt@PrintTimings   = True          ; Optional

    Opt@InterpMethod   = "bilinear"    ; "patch", "conserve"

    var_regrid = ESMF_regrid(var,Opt)

    ofile->var_regrid = varname    ;; my attempt to write to output file
                                   ; not sure if syntax is right
;;; gets:
;;;file_ext_q: <Undefined>  
;;;fatal:["FileSupport.c":4017]:_NclCreateFile: Can not open file: <regrid.nc> properly.

    printVarSummary(var_regrid)          ; Make sure this looks okay!
end

;;;This result from printVarSummary seems right:
;;;Variable: var_regrid
;;;Type: float
;;;Total Size: 1814400 bytes
;;;            453600 values
;;;Number of Dimensions: 3
;;;Dimensions and sizes:   [forecast_time0 | 7] x [lat | 180] x [lon | 360]
;;;Coordinates: 
;;;            forecast_time0: [2..8]
;;;            lat: [89.5..-89.5]
;;;            lon: [ 0.5..359.5]
;;;Number Of Attributes: 12
;;;  missing_value :       1e+20
;;;  remap :       remapped via ESMF_regrid_with_weights: Bilinear remapping
;;;  initial_time :        07/08/2014 (00:00)
;;;  model :       Climate Data Assimilation System 2 (CDAS2)
;;;  parameter_number :    59
;;;  parameter_table_version :     2
;;;  grid_number : 3
;;;  level_indicator :     1
;;;  _FillValue :  1e+20
;;;  units :       kg/m^2/s
;;;  long_name :   Precipitation rate
;;;  center :      US National Weather Service - NCEP (WMC)