DKRZ PyNGL map tickmark example mask Lambert Conformal projectionΒΆ

Example script:

#
#  File:
#    mptick_10.py
#
#  Synopsis:
#    Demonstrates how to mask Lambert Conformal Projection map.
#    Shows how to add your own longitude/latitude labels to a
#    masked Lambert Conformal plot.
#
#  Categories:
#    map plot
#
#  Based on NCL example:
#    mptick_10.ncl
#
#  Author:
#    Karin Meier-Fleischer
#
#  Date of initial publication:
#    November 2018
#
#  Description:
#    This example shows how to create a map.
#
#  Effects illustrated:
#    o  Adding longitude/latitude labels to a masked Lambert Conformal map
#    o  Moving the main title up
#    o  Attaching text strings to the outside of a plot
#    o  Converting lat/lon values to NDC values
#    o  Changing the angle of text strings
#    o  Adding a carriage return to a text string using a function code
#
#  Output:
#    Two visualizations are produced.
#
'''
  PyNGL Example:     mptick_10.py

  -  Adding longitude/latitude labels to a masked Lambert Conformal map
  -  Moving the main title up
  -  Attaching text strings to the outside of a plot
  -  Converting lat/lon values to NDC values
  -  Changing the angle of text strings
  -  Adding a carriage return to a text string using a function code

'''
from __future__ import print_function
import numpy as np
import Ngl

#-------------------------------------------------------
# Function to attach lat/lon labels to a Robinson plot
#-------------------------------------------------------
def add_labels_lcm(wks,map,dlat,dlon):
    PI         = 3.14159
    RAD_TO_DEG = 180./PI

    #-- determine whether we are in northern or southern hemisphere
    if (float(minlat) >= 0. and float(maxlat) > 0.):
        HEMISPHERE = "NH"
    else:
        HEMISPHERE = "SH"

    #-- pick some "nice" values for the latitude labels.
    lat_values = np.arange(int(minlat),int(maxlat),10)
    lat_values = lat_values.astype(float)
    nlat       = len(lat_values)

    #-- We need to get the slope of the left and right min/max longitude lines.
    #-- Use NDC coordinates to do this.
    lat1_ndc = 0.
    lon1_ndc = 0.
    lat2_ndc = 0.
    lon2_ndc = 0.
    lon1_ndc,lat1_ndc = Ngl.datatondc(map,minlon,lat_values[0])
    lon2_ndc,lat2_ndc = Ngl.datatondc(map,minlon,lat_values[nlat-1])
    slope_lft         = (lat2_ndc-lat1_ndc)/(lon2_ndc-lon1_ndc)

    lon1_ndc,lat1_ndc = Ngl.datatondc(map,maxlon,lat_values[0])
    lon2_ndc,lat2_ndc = Ngl.datatondc(map,maxlon,lat_values[nlat-1])
    slope_rgt         = (lat2_ndc-lat1_ndc)/(lon2_ndc-lon1_ndc)

    #-- set some text resources
    txres               = Ngl.Resources()
    txres.txFontHeightF = 0.01
    txres.txPosXF       = 0.1

    #-- Loop through lat values, and attach labels to the left and right edges of
    #-- the masked LC plot. The labels will be rotated to fit the line better.
    dum_lft       = []                            #-- assign arrays
    dum_rgt       = []                            #-- assign arrays
    lat_label_lft = []                            #-- assign arrays
    lat_label_rgt = []                            #-- assign arrays

    for n in range(0,nlat):
    #-- left label
      if(HEMISPHERE == "NH"):
         rotate_val = -90.
         direction  = "N"
      else:
         rotate_val =  90.
         direction  = "S"

    #-- add extra white space to labels
      lat_label_lft.append("{}~S~o~N~{}              ".format(str(np.abs(lat_values[n])),direction))
      lat_label_rgt.append("              {}~S~o~N~{}".format(str(np.abs(lat_values[n])),direction))

      txres.txAngleF = RAD_TO_DEG * np.arctan(slope_lft) + rotate_val

      dum_lft.append(Ngl.add_text(wks,map,lat_label_lft[n],minlon,lat_values[n],txres))

    #-- right label
      if(HEMISPHERE == "NH"):
         rotate_val =  90
      else:
         rotate_val = -90

      txres.txAngleF = RAD_TO_DEG * np.arctan(slope_rgt) + rotate_val

      dum_rgt.append(Ngl.add_text(wks,map,lat_label_rgt[n],maxlon,lat_values[n],txres))

    #----------------------------------------------------------------------
    # Now do longitude labels. These are harder because we're not adding
    # them to a straight line.
    # Loop through lon values, and attach labels to the bottom edge for
    # northern hemisphere, or top edge for southern hemisphere.
    #----------------------------------------------------------------------
    del(txres.txPosXF)
    txres.txPosYF = -5.0

    #-- pick some "nice" values for the longitude labels
    lon_values = np.arange(int(minlon+10),int(maxlon-10),10).astype(float)
    lon_values = np.where(lon_values > 180, 360-lon_values, lon_values)
    nlon       = lon_values.size

    dum_bot    = []                            #-- assign arrays
    lon_labels = []                            #-- assign arrays

    if(HEMISPHERE == "NH"):
       lat_val    = minlat
    else:
       lat_val    = maxlat

    ctrl = "~C~"

    for n in range(0,nlon):
      if(lon_values[n] < 0):
         if(HEMISPHERE == "NH"):
            lon_labels.append("{}~S~o~N~W{}".format(str(np.abs(lon_values[n])),ctrl))
         else:
            lon_labels.append("{}{}~S~o~N~W".format(ctrl,str(np.abs(lon_values[n]))))
      elif(lon_values[n] > 0):
         if(HEMISPHERE == "NH"):
            lon_labels.append("{}~S~o~N~E{}".format(str(lon_values[n]),ctrl))
         else:
            lon_labels.append("{}{}~S~o~N~E".format(ctrl,str(lon_values[n])))
      else:
         if(HEMISPHERE == "NH"):
            lon_labels.append("{}0~S~o~N~{}".format(ctrl,ctrl))
         else:
            lon_labels.append("{}0~S~o~N~{}".format(ctrl,ctrl))

    #-- For each longitude label, we need to figure out how much to rotate
    #-- it, so get the approximate slope at that point.
      if(HEMISPHERE == "NH"):             #-- add labels to bottom of LC plot
         lon1_ndc,lat1_ndc = Ngl.datatondc(map, lon_values[n]-0.5, minlat)
         lon2_ndc,lat2_ndc = Ngl.datatondc(map, lon_values[n]+0.5, minlat)
         txres.txJust = "TopCenter"
      else:                               #-- add labels to top of LC plot
         lon1_ndc,lat1_ndc = Ngl.datatondc(map, lon_values[n]+0.5, maxlat)
         lon2_ndc,lat2_ndc = Ngl.datatondc(map, lon_values[n]-0.5, maxlat)
         txres.txJust = "BottomCenter"

      slope_bot = (lat1_ndc-lat2_ndc)/(lon1_ndc-lon2_ndc)
      txres.txAngleF  =  RAD_TO_DEG * np.arctan(slope_bot)

    #-- attach to map
      dum_bot.append(Ngl.add_text(wks, map, str(lon_labels[n]), \
                                  lon_values[n], lat_val, txres))
    return

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

    wks = Ngl.open_wks("png","plot_mptick_10")              #-- open workstation

    #-----------------------------------
    #-- first plot: Lambert Conformal
    #-----------------------------------
    #-- northern hemisphere
    minlon = -90.                                           #-- min lon to mask
    maxlon =  40.                                           #-- max lon to mask
    minlat =  20.                                           #-- min lat to mask
    maxlat =  80.                                           #-- max lat to mask

    mpres                        =  Ngl.Resources()         #-- resource object
    mpres.nglMaximize            =  True
    mpres.nglDraw                =  False                   #-- turn off plot draw and frame advance. We will
    mpres.nglFrame               =  False                   #-- do it later after adding subtitles.

    mpres.mpFillOn               =  True                    #-- turn map fill on
    mpres.mpOutlineOn            =  False                   #-- outline map
    mpres.mpOceanFillColor       = "Transparent"            #-- set ocean fill color to transparent
    mpres.mpLandFillColor        = "Gray90"                 #-- set land fill color to gray
    mpres.mpInlandWaterFillColor = "Gray90"                 #-- set inland water fill color to gray

    mpres.tiMainString           = "Adding lat/lon labels to a masked LC map~C~(northern hemisphere)"
    mpres.tiMainOffsetYF         =  0.05
    mpres.tiMainFontHeightF      =  0.016                   #-- decrease font size

    mpres.mpProjection           = "LambertConformal"
    mpres.nglMaskLambertConformal = True                    #-- turn on lc masking
    mpres.mpLambertParallel1F    =  10
    mpres.mpLambertParallel2F    =  70
    mpres.mpLambertMeridianF     = -100
    mpres.mpLimitMode            = "LatLon"
    mpres.mpMinLonF              =  minlon
    mpres.mpMaxLonF              =  maxlon
    mpres.mpMinLatF              =  minlat
    mpres.mpMaxLatF              =  maxlat
    mpres.mpGridAndLimbOn        =  True
    mpres.mpGridSpacingF         =  10.

    mpres.pmTickMarkDisplayMode  = "Always"

    #-- create and draw the basic map
    map = Ngl.map(wks,mpres)

    #-- add labels to the plot
    tx = add_labels_lcm(wks,map,10,10)

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

    #-----------------------------------
    #-- second plot: Mercator projection
    #-----------------------------------
    #-- southern hemisphere
    minlat = -80.                                           #-- min lat to mask
    maxlat = -20.                                           #-- max lat to mask

    mpres.mpMinLatF              =  minlat
    mpres.mpMaxLatF              =  maxlat

    mpres.tiMainString           = "Adding lat/lon labels to a masked LC map~C~(southern hemisphere)"

    #-- create and draw the basic map
    map = Ngl.map(wks,mpres)

    #-- add labels to the plot
    tx = add_labels_lcm(wks,map,10,10)

    #-- maximize the plot, draw it and advance the frame
    Ngl.maximize_plot(wks,map)
    Ngl.draw(map)
    Ngl.frame(wks)

    Ngl.end()

if __name__ == '__main__':
    main()

Result: PyNgl mptick 10.1 w400

PyNgl mptick 10.2 w400