DKRZ PyNGL example streamline plot

Example:

from __future__ import print_function
import Ngl,Nio

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

    #-- open a file and read variables
    f    = Nio.open_file("rectilinear_grid_2D.nc", "r")

    u    = f.variables["u10"]
    v    = f.variables["v10"]
    ua   = f.variables["u10"][0,:,:]
    va   = f.variables["v10"][0,:,:]

    lat  = f.variables["lat"]
    lon  = f.variables["lon"]
    nlon = len(lon)
    nlat = len(lat)

    #-- open a workstation
    wks = Ngl.open_wks("png","plot_TRANS_streamline_py")

    #-- resource settings
    stres                        =  Ngl.Resources()
    stres.nglFrame               =  False

    stres.vfXArray               =  lon[::3]
    stres.vfYArray               =  lat[::3]

    stres.mpFillOn               =  True
    stres.mpOceanFillColor       = "Transparent"
    stres.mpLandFillColor        = "Gray90"
    stres.mpInlandWaterFillColor = "Gray90"

    #-- create the plot, use every 3rd data value
    plot = Ngl.streamline_map(wks,ua[::3,::3],va[::3,::3],stres)

    #-- write variable long_name and units to the plot
    txres               = Ngl.Resources()
    txres.txFontHeightF = 0.014

    Ngl.text_ndc(wks,f.variables["u10"].attributes['long_name'],0.16,0.76,txres)
    Ngl.text_ndc(wks,f.variables["u10"].attributes['units'],    0.95,0.76,txres)

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

    Ngl.end()

if __name__ == '__main__':
    main()

Result: