Graph Plot with Double Y Axis

# (C) Copyright 2017- ECMWF.
#
# This software is licensed under the terms of the Apache Licence Version 2.0
# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
#
# In applying this licence, ECMWF does not waive the privileges and immunities
# granted to it by virtue of its status as an intergovernmental organisation
# nor does it submit to any jurisdiction.
#

import metview as mv

# -------------------------------------------------------------------------
# Description: Demonstrates how to make a graph plot with two vertical axes
# -------------------------------------------------------------------------

# We will compute a vertical profile from a point in a data set
# that is on model levels. This will be plotted with model levels
# as the left-hand vertical axis, and computed pressure levels on the
# right-hand vertical axis.

# read the input model level grib file
filename = "fc_ml.grib"
if mv.exist(filename):
    g = mv.read(filename)
else:
    g = mv.gallery.load_dataset(filename)

# read the LNSP file
filename = "lnsp.grib"
if mv.exist(filename):
    lnsp_data = mv.read(filename)
else:
    lnsp_data = mv.gallery.load_dataset(filename)


# define profile location
lat_lon_point = [56.9, -2.6]

# read temperature data
t_data = mv.read(data=g, parameter="t")

model_levels = mv.grib_get_long(t_data, "level")

iv1 = mv.input_visualiser(
    input_x_values=mv.nearest_gridpoint(t_data, lat_lon_point),
    input_y_values=model_levels,
)

dots = mv.msymb(symbol_type="marker", symbol_outline="on", symbol_marker_index=15)

# compute pressure levels for the input model levels
pressure_fields = mv.pressure(lnsp_data, t_data)
pressure_levels = mv.nearest_gridpoint(pressure_fields, lat_lon_point)
pressure_levels = [x / 100 for x in pressure_levels]

# Construct two Cartesian views; the first will be plotted with data, the
# second will be plotted without data in order to plot just its vertical axis

# set up the main Cartesian view - it has a left-hand vertical axis
primary_vertical_axis = mv.maxis(
    axis_orientation="vertical",
    axis_title_text="model levels",
    axis_title_height=0.5,
    axis_tick_label_hight=0.5,
)

c1 = mv.cartesianview(
    y_min=max(model_levels),  # larger level usually at bottom
    y_max=min(model_levels),
    x_min=180,  # Kelvin
    x_max=320,  # Kelvin
    vertical_axis=primary_vertical_axis,
)

# set up the secondary Cartesian view with a right-hand vertical axis
secondary_vertical_axis = mv.maxis(
    axis_orientation="vertical",
    axis_position="right",
    axis_title_text="pres levels",
    axis_title_height=0.5,
    axis_tick_label_hight=0.5,
)

# switch off the plotting of its horizontal axis
secondary_horizontal_axis = mv.maxis(
    axis_line="off", axis_tick="off", axis_tick_label="off"
)

c2 = mv.cartesianview(
    y_min=max(pressure_levels),
    y_max=min(pressure_levels),
    vertical_axis=secondary_vertical_axis,
    horizontal_axis=secondary_horizontal_axis,
)

# set up the pages that will use these views
p1 = mv.plot_page(view=c1)
p2 = mv.plot_page(view=c2)
dw = mv.plot_superpage(pages=[p1, p2])

# define the output plot file
mv.setoutput(mv.pdf_output(output_name="double_axis_1"))

# plot the data into the first view, then plot the second view empty
mv.plot(dw[0], iv1, dots, dw[1])