DKRZ PyNGL example plot curvilinear data

Note

We will use xarray in the future exclusively for reading and writing data files because at the beginning of 2019 NCAR has decided to freeze PyNIO until further notice.

Example script:

'''
Script:
    curvilinear_data_CORDEX_EUR-11.py

Description:
    Example of how to plot curvilinear data.

Effects illustrated:
    - Plotting curvilinear data
    - Filled contour plot
'''
import os
import numpy as np
import xarray as xr
import Ngl

#-----------------------------------------------------------------------
#-- Function:   add_titles(wks,plot,resources,title,left,center,right)
#-----------------------------------------------------------------------
def add_titles(wks,plot,title="",left="",center="",right=""):
   vpx = Ngl.get_float(plot,"vpXF")             #-- retrieve value of res.vpXF from plot
   vpy = Ngl.get_float(plot,"vpYF")             #-- retrieve value of res.vpYF from plot
   vpw = Ngl.get_float(plot,"vpWidthF")         #-- retrieve value of res.vpWidthF from plot
   vph = Ngl.get_float(plot,"vpHeightF")        #-- retrieve value of res.vpHeightF from plot

   ymax = vpy+0.08                              #-- we need space for the title and strings

   if(ymax > 0.98):
      print("--> if you can't see the title use res.nglMaximize = False and/or set res.vpYF")

#-- add title
   if(title != ""):
      tires = Ngl.Resources()
      tires.txFontHeightF =  0.018
      tires.txJust        = "CenterCenter"
      tires.txFont        =  22                     #-- Font 22: Helvetica bold
      if(left != "" or center != "" or right != ""):
         y = vpy + 0.06
      else:
         y = vpy + 0.04

      vpxc = vpx + (vpw/2)
      Ngl.text_ndc(wks, title, vpxc, y, tires)

#-- add left, center and/or right string
   txres = Ngl.Resources()
   txres.txFontHeightF = 0.014                  #-- font size for left, center and right string

   y = vpy + 0.02                               #-- y-position

   if(left != ""):
      txres.txJust = "CenterLeft"               #-- text justification
      x = vpx                                   #-- x-position
      Ngl.text_ndc(wks, left, x, y, txres)      #-- add text to wks

   if(center != ""):
      txres.txJust = "CenterCenter"             #-- text justification
      Ngl.text_ndc(wks, center, 0.5, y, txres)  #-- add text to wks

   if(right != ""):
      txres.txJust = "CenterRight"              #-- text justification
      x = vpx+vpw                               #-- x-position
      Ngl.text_ndc(wks, right, x, y, txres)     #-- add text to wks

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

    #-- set file name
    home  =  os.environ.get('HOME')
    diri  = 'data/CORDEX/EUR-11'
    fname = 'tas_EUR-11_MPI-M-MPI-ESM-LR_rcp45_r1i1p1_CLMcom-CCLM4-8-17_v1_mon_200601-201012.nc'

    file_name = os.path.join(home,diri,fname)

    #-- variable name
    varname = 'tas'

    #-- open file
    ds = xr.open_dataset(file_name)

    #-- read the variables
    var   = ds[varname][0,:,:]
    lat2d = ds['lat']                           #-- 2D coordinate
    lon2d = ds['lon']                           #-- 2D coordinate

    print('lat2d.shape: {}'.format(lat2d.shape))
    print('lon2d.shape: {}'.format(lon2d.shape))

    #-- open a workstation
    wks_type              = "png"               #-- output type
    wks                   =  Ngl.open_wks(wks_type,'plot_curvilinear_data_CORDEX_EUR-11')

    #-- set resources
    res                   =  Ngl.Resources()    #-- generate an resources object for plot
    res.nglFrame          =  False
    res.nglMaximize       =  True

    res.cnFillOn          =  True               #-- turn on contour fill
    res.cnLinesOn         =  False              #-- don't draw contour lines
    res.cnLineLabelsOn    =  False              #-- don't draw line labels
    res.cnFillPalette     = "BlueYellowRed"     #-- set color map
    res.cnLevelSelectionMode  = "ManualLevels"
    res.cnMinLevelValF    =  250
    res.cnMaxLevelValF    =  290
    res.cnLevelSpacingF   =  2

    res.lbOrientation     = "Horizontal"        #-- labelbar orientation

    res.sfXArray          =  lon2d.values       #-- longitude grid cell center
    res.sfYArray          =  lat2d.values       #-- latitude grid cell center

    res.mpFillOn          =  False              #-- don't draw filled map
    res.mpGridLatSpacingF =  10.                #-- grid lat spacing
    res.mpGridLonSpacingF =  10.                #-- grid lon spacing
    res.mpDataBaseVersion = "MediumRes"         #-- map database
    res.mpLimitMode       = "LatLon"            #-- must be set using minLatF/maxLatF/minLonF/maxLonF
    res.mpMinLatF         =  15.                #-- sub-region minimum latitude
    res.mpMaxLatF         =  80.                #-- sub-region maximum latitude
    res.mpMinLonF         = -50.                #-- sub-region minimum longitude
    res.mpMaxLonF         =  70.                #-- sub-region maximum longitude

    #-- create the plot
    plot = Ngl.contour_map(wks,var,res)         #-- create the contour plot

    #-- add the title and left, center and/or right string
    title = "Curvilinear grid:  tas (CORDEX EUR-11)"   #-- main title string

    if var.attrs['units']:                      #-- retrieve units attribute
       units = var.attrs['units']

    add_titles(wks,plot,title=title,left=varname,right=units)

    #-- advance the frame
    Ngl.frame(wks)

    #-- end
    Ngl.end()

if __name__ == '__main__':
    main()

Result: