Draw the domain in `plot_snaphot.py`

In `plot_snapshot.py`, read `grid_nml.txt` and draw a rectangle
showing the domain.

Analysis/plot_snapshot.py

@@ -153,6 +153,8 @@ def snapshot(directory, k = None, *, dashed = False, light = False,
 if __name__ == "__main__":
     import argparse
     import sys
+    import f90nml
+    from matplotlib import patches
     
     parser = argparse.ArgumentParser()
     parser.add_argument("-v", "--velocity", help = "plot velocity field",
@@ -207,6 +209,13 @@ if __name__ == "__main__":
         ax.plot(lon_2d.reshape(-1), lat_2d.reshape(-1), transform = src_crs,
                 marker = "+", color = "gray", linestyle = "None")
 
+    file = path.join(args.directory, "grid_nml.txt")
+    grid_nml = f90nml.read(file)["grid_nml"]
+    rect = patches.Rectangle(grid_nml["corner_deg"],
+                             (grid_nml["nlon"] - 1) * 0.25,
+                             (grid_nml["nlat"] - 1) * 0.25, edgecolor="black",
+                             fill=False)
+    ax.add_patch(rect)
     snapshot(args.directory, args.k, dashed = args.dashed,
              light = args.light, window = args.window)