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PyNGL example unstructured contour plot

This script creates a contour plot of unstructured data, in this case data from the ICON model.

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

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()

Plot result:

PyNGL unstructured data contour plot w400

 

 

 

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