"""
  NCL User Guide Python Example:   PyNGL_rectilinear_slice.py

   - slice filled contour plot
   - colorbar
   - log axis
   
  2015-06-04  kmf
"""
import numpy as np
import sys,os
import Nio, Ngl

def nice_lon_labels(lons):
  lonstrs = []
  for l in lons:
    if l < 0:
      lonstrs.append("%i~S~o~N~W" % np.fabs(l))
    elif l > 0:
      lonstrs.append("%i~S~o~N~E" % l)
    else:
      lonstrs.append("EQ" % l)
  return lonstrs


#--  define variables
diri   = "./"                             #-- data directory
fname  = "rectilinear_grid_3D.nc"         #-- data file name

#---Test if file exists
if(not os.path.exists(diri+fname)):
  print("You do not have the necessary file (%s) to run this example." % (diri+fname))
  print("You can get the files from the NCL website at:")
  print("http://www.ncl.ucar.edu/Document/Manuals/NCL_User_Guide/Data/")
  sys.exit()

#--  open file and read variables
f      =  Nio.open_file(diri + fname,"r") #-- open data file
t      =  f.variables["t"]                #-- get whole "t" variable
t26    =  t[0,:,26,:]                     #-- variable at lat index 26
lev    =  f.variables["lev"][:]*0.01      #-- all levels, convert to hPa
lat    =  f.variables["lat"][:]           #-- reverse latitudes
lon    =  f.variables["lon"][:]           #-- all longitudes

t26,lon = Ngl.add_cyclic(t26,lon)

strlat26 = lat[26]                        #-- retrieve data of lat index 26

#-- get the minimum and maximum of the data
minval =  int(np.amin(t[:]))           #-- minimum value
maxval =  int(np.amax(t[:]))           #-- maximum value
inc    =  5                            #-- contour level spacing

#-- values on which to place tickmarks on X and Y axis
lons = np.arange(-180,240,60)
levs = [1000,700,500,400,300,200,150,100,70,50,30,10]

wks =  Ngl.open_wks("png","plot_rectilinear_slice_ngl")
                                          #-- open workstation
#-- set resources
res                       =  Ngl.Resources

res.tiMainString          =  "%s (%s) at lat %.2f degrees" % \
                              (t.long_name,t.units,strlat26)
res.cnLevelSelectionMode  = "ManualLevels" #-- select manual levels
res.cnMinLevelValF        =  minval       #-- minimum contour value
res.cnMaxLevelValF        =  maxval       #-- maximum contour value
res.cnLevelSpacingF       =  inc          #-- contour increment

res.cnFillOn              =  True         #-- turn on contour fill.
res.cnLineLabelsOn        =  False        #-- turn off line labels.
res.cnInfoLabelOn         =  False        #-- turn off info label.
res.cnFillPalette         = "BlueWhiteOrangeRed" #-- set color map.
res.pmLabelBarOrthogonalPosF = -0.03      #-- move labelbar close to plot

res.sfXArray              =  lon          #-- scalar field x
res.sfYArray              =  lev          #-- scalar field y

res.trYReverse            = True          #-- reverse the Y axis
res.nglYAxisType          = "LogAxis"     #-- y axis log

res.tiYAxisString         = "%s (hPa)" % f.variables["lev"].long_name

res.nglPointTickmarksOutward = True       #-- point tickmarks out

res.tmYLMode              = "Explicit"    #-- set y axis tickmark labels
res.tmXBMode              = "Explicit"    #-- set x axis tickmark labels
res.tmYLValues            = levs
res.tmXBValues            = lons
res.tmYLLabels            = map(str,levs)
res.tmXBLabels            = nice_lon_labels(lons)

res.tmXBLabelFontHeightF  = 0.015        # - make font smaller
res.tmYLLabelFontHeightF  = 0.015

map = Ngl.contour(wks,t26,res)            #-- draw contours 

#-- end
Ngl.end()