PyNGL example unstructured contour plot

Software requirements:

• Python 2.7.x

• Numpy 1.9.2

• PyNGL/PyNIO 1.5.0

Run the unstructured contour example script:

python PyNGL_unstructured_contour_cellfill.py

Script PyNGL_unstructured_contour_cellfill.py:

'''
 DKRZ PyNGL script: PyNGL_unstructured_contour_cellfill.py

 Description:       Python script using PyNGL Python module
                    - contour plot
                    - CellFill
                    - unstructured data (ICON)

 2015-06-05  meier-fleischer(at)dkrz.de
'''
import numpy as np
import math, time
import sys,os
import Ngl, Nio

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

    t1 = time.time()                                   #-- retrieve start time
    print ""

    #--  define variables
    diri  = "./"                                       #-- data path
    fname = "ta_ps_850.nc"                             #-- data file
    gname = "r2b4_amip.nc"                             #-- grid info file

    #--  open file and read variables
    f = Nio.open_file(diri + fname,"r")                #-- add data file
    g = Nio.open_file(diri +"/grids/"+ gname,"r")      #-- add grid file (not contained in data file!!!)

    #-- read a timestep of "ta"
    var =  f.variables["ta"][0,0,:]                    #-- first time step, lev, ncells

    print "-----------------------"
    print f.variables["ta"]                            #-- like printVarSummary
    print "-----------------------"

    title    = "ICON:  Surface temperature"            #-- title string
    varMin   =  230                                    #-- data minimum
    varMax   =  310                                    #-- data maximum
    varInt   =    5                                    #-- data increment
    levels   =  range(varMin,varMax,varInt)            #-- set levels array

    #-- define the x-, y-values and cell bounds
    rad2deg = 45./np.arctan(1.)                        #-- radians to degrees

    x      =  g.variables["clon"][:]                   #-- read clon
    y      =  g.variables["clat"][:]                   #-- read clat
    vlon   =  g.variables["clon_vertices"][:]          #-- read clon_vertices
    vlat   =  g.variables["clat_vertices"][:]          #-- read clat_vertices

    ncells =  vlon.shape[0]                            #-- number of cells
    nv     =  vlon.shape[1]                            #-- number of edges

    x      =  x    * rad2deg                           #-- cell center, lon
    y      =  y    * rad2deg                           #-- cell center, lat
    vlat   =  vlat * rad2deg                           #-- cell lattitude vertices
    vlon   =  vlon * rad2deg                           #-- cell longitude vertices

    #-- longitude values -180. to 180.
    for j in xrange(1,ncells):
        for i in range(1,nv):
            if vlon[j,i] < -180. :
               vlon[j,i] = vlon[j,i] + 360.
            if vlon[j,i] > 180. :
               vlon[j,i] = vlon[j,i] - 360.

    #-- information
    print "Cell points:           ", nv
    print "Cells:                 ", str(ncells)
    print "Variable ta   min/max:  %.2f " % np.min(var) + "/" + " %.2f" % np.max(var)
    print ""

    #-- open a workstation
    wkres                 =  Ngl.Resources()      #-- generate an resources object for workstation
    wkres.wkWidth         =  1024                 #-- width of workstation
    wkres.wkHeight        =  1024                 #-- height of workstation
    wks_type              = "png"                 #-- output type
    wks      =  Ngl.open_wks(wks_type,"Py_ICON_cellfill_2") #-- open a workstation

    #-- set resources
    res                      =  Ngl.Resources()        #-- plot mods desired.
    res.nglDraw              =  False                  #-- turn off plot draw and frame advance. We will
    res.nglFrame             =  False                  #-- do it later after adding subtitles

    #-- contour resources
    res.cnFillOn             =  True                   #-- color plot desired
    res.cnFillMode           = "CellFill"              #-- set fill mode
    res.cnFillPalette        = "BlueWhiteOrangeRed"    #-- choose colormap
    res.cnLinesOn            =  False                  #-- turn off contour lines
    res.cnLineLabelsOn       =  False                  #-- turn off contour labels
    res.cnLevelSelectionMode = "ExplicitLevels"        #-- use explicit levels
    res.cnLevels             =  levels                 #-- set levels

    #-- labelbar resources
    res.lbOrientation        = "Horizontal"            #-- vertical by default
    res.lbBoxLinesOn         =  False                  #-- turn off labelbar boxes
    res.lbLabelFontHeightF   =  0.01                   #-- labelbar label font size

    #-- map resources
    res.mpFillOn             =  False                  #-- don't use filled map
    res.mpGridAndLimbOn      =  False                  #-- don't draw grid lines

    #-- grid resources
    res.sfXArray             =  x                      #-- transform x to mesh scalar field
    res.sfYArray             =  y                      #-- transform y to mesh scalar field
    res.sfXCellBounds        =  vlon                   #-- needed if set cnFillMode = "CellFill"
    res.sfYCellBounds        =  vlat                   #-- needed if set cnFillMode = "CellFill"

    #-- title string resources
    res.tiMainString         = "ICON grid - CellFill"  #-- title string
    res.tiMainOffsetYF       =  0.03                   #-- move main title towards plot

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

    #-- draw the plot and advance the frame
    Ngl.draw(plot)
    Ngl.frame(wks)

    #-- get wallclock time
    t2 = time.time()
    print "Wallclock time:  %0.3f seconds" % (t2-t1)
    print ""

    #-- done
    Ngl.end()

if __name__ == '__main__':
    main()

Result: