DKRZ PyNGL example regridding with xesmf

Example script:

#
#  File:
#    TRANS_regrid_xesmf_rectilinear_to_rectilinear.py
#
#  Synopsis:
#    Illustrates how to create a contour fill plot on a map
#
#  Categories:
#    contour plot
#    map plot
#
#  Author:
#    Karin Meier-Fleischer, based on NCL example
#
#  Date of initial publication:
#    October 2018
#
#  Description:
#    This example shows how to create a contour fill plot on a map.
#
#  Effects illustrated:
#    o  Drawing a contour fill plot
#    o  Drawing a map
#
#  Output:
#    Two visualizations are produced, original data and regridded data.
#
#  Notes: The data for this example can be downloaded from
#    http://www.ncl.ucar.edu/Document/Manuals/NCL_User_Guide/Data/
#
'''
  Transition Guide Python Example:     TRANS_regrid_xesmf_rectilinear_to_rectilinear.py

  - read netCDF file
  - regrid to higher resolution grid
  - drawing contour fill plots
  - drawing a map

  18-10-15  kmf
'''
from __future__ import print_function
import numpy as np
import xarray as xr
import xesmf as xe
import Ngl

#-----------------------------------------------------------------------
#-- Function: main
#-----------------------------------------------------------------------
def main():

    #--  open file and read variables
    data = xr.open_dataset("rectilinear_grid_3D.nc")

    t   = data['t'][0,0,:,:]
    lat = np.array(data['lat'][:])
    lon = np.array(data['lon'][:])

    #-- destination lat/lon
    dst_lat = np.arange(-89.5,90.5,1.0)
    dst_lon = np.arange(-179.5,180.5,1.0)

    #-- init destination grid
    dstgrid = xr.Dataset({'lat': (['lat'], dst_lat),
                          'lon': (['lon'], dst_lon),})

    #-- regrid
    regridder = xe.Regridder(data, dstgrid, 'bilinear')

    t_regrid   = regridder(t)
    lat_regrid = regridder(t).lat
    lon_regrid = regridder(t).lon

    #-- plotting
    wks = Ngl.open_wks("png","plot_TRANS_regrid_xesmf_py")

    res                 =  Ngl.Resources()
    res.nglFrame        =  False
    res.cnFillOn        =  True
    res.cnFillPalette   = "NCL_default"
    res.cnLineLabelsOn  =  False
    res.cnLevelSelectionMode = "ManualLevels"   #-- use manual contour line levels
    res.cnMinLevelValF  =  235.0                #-- contour min. value
    res.cnMaxLevelValF  =  310.0                #-- contour max. value
    res.cnLevelSpacingF =    5.0                #-- contour interval
    res.lbOrientation   = "horizontal"

    res.sfXArray        =  dst_lon
    res.sfYArray        =  dst_lat

    plot = Ngl.contour_map(wks,t_regrid,res)

    Ngl.frame(wks)

    res.sfXArray        =  lon
    res.sfYArray        =  lat

    plot = Ngl.contour_map(wks,t,res)

    Ngl.frame(wks)

    #-- clean-up
    regridder.clean_weight_file()


#-- call  main function
if __name__ == '__main__':
    main()