Merge pull request #477 from NCAR/panel_31

Panel 31

Gallery/Panels/NCL_panel_31.py

@@ -0,0 +1,136 @@
+"""
+NCL_panel_31.py
+===============
+This script illustrates the following concepts:
+   - Paneling 8 plots on a page
+   - Adding a common title to paneled plots
+   - Overlaying an image onto a map
+   - Adding a vector field to a map
+
+See following URLs to see the reproduced NCL plot & script:
+    - Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/panel_31.ncl
+    - Original NCL plot: https://www.ncl.ucar.edu/Applications/Images/panel_31_lg.png
+"""
+
+###############################################################################
+# Import packages:
+
+import numpy as np
+import matplotlib.pyplot as plt
+import cartopy.crs as ccrs
+import xarray as xr
+
+import geocat.viz as gv
+import geocat.datafiles as gdf
+
+###############################################################################
+# Read in Data:
+
+# Read in the image file
+fname = gdf.get('image_files/EarthMap.jpg')
+img = plt.imread(fname)
+
+# Read in the vector data using xarray
+ds = xr.open_dataset(gdf.get("netcdf_files/uvt.nc")).isel(time=0)
+
+# Select zonal and meridional wind
+U = ds.U
+V = ds.V
+
+# Select latitude and longitudes
+lat = ds.lat
+lon = ds.lon
+
+###############################################################################
+# Plot:
+
+# Create a figure and axes
+fig, axs = plt.subplots(ncols=2,
+                        nrows=4,
+                        figsize=(15.5, 18),
+                        subplot_kw={'projection': ccrs.PlateCarree()})
+
+# Define pressures and reshape to match subplot layout (4 rows, 2 columns)
+levs = np.array([1000, 850, 700, 500, 400, 300, 250, 200])
+pressure = np.reshape(levs, (4, 2))
+
+# Define image extent. This image is of the entire globe, so extent covers all latitudes and longitudes
+img_extent = (-180, 180, -90, 90)
+
+# Loop through each axes and plot
+# Loop through each row
+for i in range(4):
+    # Loop through each column
+    for j in range(2):
+        # Set axes
+        ax = axs[i][j]
+
+        # Set extent of the map
+        ax.set_extent([65, 95, 5, 25])
+
+        # add the image. The "origin" of the image is in the upper left corner
+        ax.imshow(img,
+                  origin='upper',
+                  extent=img_extent,
+                  transform=ccrs.PlateCarree())
+        ax.coastlines(resolution='50m', color='black', linewidth=1)
+
+        # Add vectors onto the plot
+        Q = ax.quiver(lon,
+                      lat,
+                      U.sel(lev=pressure[i][j]),
+                      V.sel(lev=pressure[i][j]),
+                      color='white',
+                      pivot='middle',
+                      width=.0025,
+                      scale=75)
+
+        # Use geocat-viz utility function to format lat/lon tick labels
+        gv.add_lat_lon_ticklabels(ax=ax)
+
+        # Use geocat-viz utility function to customize tick marks
+        gv.set_axes_limits_and_ticks(ax,
+                                     xlim=(65, 95),
+                                     ylim=(5, 25),
+                                     xticks=range(65, 100, 5),
+                                     yticks=range(5, 27, 5))
+
+        # Customize ticks and labels
+        ax.tick_params(labelsize=11, length=8)
+
+        # Add title to the axes
+        ax.set_title(f'level={pressure[i][j]} hPa')
+
+# Add title to the figure
+plt.suptitle("Zonal Wind (m/2)", fontsize=30, y=1, x=0.45)
+
+# Draw legend for vector plot
+ax.add_patch(
+    plt.Rectangle(
+        (96.5, 5),  # xy location of rectangle
+        11,  # width
+        5.7,  # height
+        facecolor='white',
+        edgecolor='grey',
+        clip_on=False)  # allow rectangle to be visible beyond axes
+)
+
+ax.quiverkey(
+    Q,  # the quiver instance
+    0.935,  # x position of the key
+    .05,  # y position of the key
+    4,  # length of the key
+    '4',  # label for the key
+    labelpos='N',  # position the label to the 'north' of the arrow
+    color='black',  # arrow color
+    coordinates='figure',
+    fontproperties={'size': 20},
+    labelsep=0.1,  # Distance between arrow and label
+)
+
+# Add text to key
+plt.text(97, 5.5, "Reference Vector", fontsize=15)
+
+# Show the plot
+plt.tight_layout()  # Auto adjusts padding on edge of figure
+plt.show()