def plot_map(filename, varname, t_index, z_index):
"""
This function plots a map from NetCDF data.
The function extracts the relevant data using functions from netcdf_utils and extract
It plots the data using functions from plotting
This function also uses the NetCDF4 library.
There is no extra error handling - the function will not work if the arguments are incorrect
The netcdf file must contain a valid latitude and longitude variable
:param filename: location of a NetCDF file as a string (in file system)
:param varname: the identifier of the variable that is to be plotted
:param t_index: index along the time axis as an integer
:param z_index: index along the vertical axis as an integer
:return: no return
"""
nc = netCDF4.Dataset(filename)
data_var = nc.variables[varname]
# Extract the required data
data = extract.extract_map_data(nc, data_var, t_index, z_index)
# Find the longitude and latitude values
lon_var = netcdf_utils.find_longitude_var(nc, data_var)
lon_vals = lon_var[:]
lat_var = netcdf_utils.find_latitude_var(nc, data_var)
lat_vals = lat_var[:]
title = "Plot of %s" % netcdf_utils.get_title(data_var)
plotting.display_map_plot(data, lon_vals, lat_vals, title)
def extract_vertical_data(nc, data_var, direction, value, t_index):
"""
This function extracts data ready to be plotted on the vertical cross section.
:param nc: a NetCDF Dataset object
:param data_var: a NetCDF Variable object representing the variable to be extracted
:param direction: the direction of the vertical section as a string
:param value: the latitude or longitude that section represents
:return: the extracted vertical profile data and coordinate data for plotting
"""
# Find the number of dimensions for the data variable
num_dims = len(data_var.dimensions)
if num_dims < 3 or num_dims > 4:
raise ValueError("Cannot extract data from variable with %d dimensions" % num_dims)
lon_var = nu.find_longitude_var(nc, data_var)
lat_var = nu.find_latitude_var(nc, data_var)
t_var = nu.find_time_var(nc, data_var)
z_var = nu.find_vertical_var(nc, data_var)
if lon_var is None or lat_var is None:
# Vertical cross section need both latitude and longitude
raise ValueError("Cannot plot vertical cross section without both \
longitude and latitude")
else:
# Determine the direction of this section and find the index of the coordinate value
if (direction == 'NS'):
sec_index = nu.find_nearest_lon_index(nc, data_var, value)
# Check the existing of vertical dimension
if z_var is None:
raise ValueError("Cannont plot vertical cross section without vertical dimension")
elif t_var is None:
# Return 3-D array, x- and z- coordinate data if time dimension does not exist
return data_var[:,:,sec_index], lat_var, z_var
else:
# Return 4-D array, x- and z- coordinate data if time dimension exists
return data_var[t_index,:,:,sec_index], lat_var, z_var
elif (direction == 'EW'):
sec_index = nu.find_nearest_lat_index(nc, data_var, value)
if z_var is None:
raise ValueError("Cannont plot vertical cross section without vertical dimension")
elif t_var is None:
return data_var[:,sec_index,:], lon_var, z_var
else:
return data_var[t_index,:,sec_index,:], lon_var, z_var
else:
raise ValueError("Need to choose the direction from NS or EW")
def plot_map(data_path, var, t_index, z_index):
# Read the netcdf file
nc = netCDF4.Dataset(data_path)
# Read the particular variable by the input parameter
data_var = nc.variables[var]
# Extract the 2-D data of this var using the extract function
data = extract.extract_map_data(nc, data_var, t_index, z_index)
# find the longitude array
lons = netcdf_utils.find_longitude_var(nc, data_var)
lons = lons[:]
# find the latitude array
lats = netcdf_utils.find_latitude_var(nc, data_var)
lats = lats[:]
# Find the title by the get_title function created before
title = netcdf_utils.get_title(data_var)
# Plot the figure by map_plot function
plotting.display_map_plot(data, lons, lats, title)
def extract_map_data(nc, data_var, t_index, z_index):
"""
This function extracts data ready to be plotted on a map. It takes 4 arguments:
nc: a NetCDF Dataset object
data_var: a NetCDF Variable object representing the variable to be extracted
t_index: the desired index along the time axis (if present) - an integer
z_index: the desired index along the z-axis (if present) - an integer
The function returns a 2D numpy array of map data
"""
# Find the number of dimensions for the data variable
num_dims = len(data_var.dimensions)
if num_dims < 2 or num_dims > 4:
# This shows an example of raising an exception if bad input means that we can't proceed further
raise ValueError("Cannot extract data from variable with %d dimensions" % num_dims)
lon_var = nu.find_longitude_var(nc, data_var)
lat_var = nu.find_latitude_var(nc, data_var)
if lon_var is None or lat_var is None:
raise ValueError("Need both latitude and longitude dimensions to extract map data")
if num_dims == 2:
# Simple case - just return all the data
return data_var[:,:]
elif num_dims == 3:
# Determine whether to use time or z axis
z_var = nu.find_vertical_var(nc, data_var)
time_var = nu.find_time_var(nc, data_var)
# Neither axis is present - throw an error
if z_var is None and time_var is None:
raise ValueError("Data is 3D but there is no vertical or time axis")
if z_var is not None:
# We have a z-axis
return data_var[z_index,:,:]
else:
# We have a time axis
return data_var[t_index,:,:]
else:
# num_dims must equal 4
return data_var[t_index,z_index,:,:]
def extract_timeseries(nc, data_var, lon, lat, z):
"""
This function extracts data ready to be plotted the time series.
:param nc: a NetCDF Dataset object
:param data_var: a NetCDF Variable object representing the variable to be extracted
:param lon: the value of longitude in degrees
:param lat: the value of latitude in degrees
:param z: the value of vertical coordinate variable
:return: the extracted data and coordinate data for plotting
"""
# Find the number of dimensions for the data variable
num_dims = len(data_var.dimensions)
# To plot time series the data should have x-, y- and t- dimensions at least
if num_dims < 3 or num_dims > 4:
raise ValueError("Cannot extract data from variable with %d dimensions" % num_dims)
lon_var = nu.find_longitude_var(nc, data_var)
lat_var = nu.find_latitude_var(nc, data_var)
t_var = nu.find_time_var(nc, data_var)
z_var = nu.find_vertical_var(nc, data_var)
if t_var is None:
# Time series plot must contain the time dimension
raise ValueError("The data does not have time dimension")
# Consider other dimensions when time diemension exists
elif lon_var is None or lat_var is None:
# Time series plot needs both latitude and longitude to determine location
raise ValueError("Cannot plot time series plot without both longitude \
and latitude")
# Check the existence of vertical axis variable
elif z_var is not None:
lon_index = nu.find_nearest_lon_index(nc, data_var, lon)
lat_index = nu.find_nearest_lat_index(nc, data_var, lat)
z_index = nu.find_nearest_z_index_index(nc, data_var, z)
return data_var[:,z_index,lat_index,lon_index], t_var
else:
lon_index = nu.find_nearest_lon_index(nc, data_var, lon)
lat_index = nu.find_nearest_lat_index(nc, data_var, lat)
return data_var[:,lat_index,lon_index], t_var