Add argument `arrows`

To function `plot_single_traj`.

Trajectories/Analysis/plot_traj.py

@@ -8,6 +8,7 @@ and markers for the extrema at initial positions.
 import random
 
 import numpy as np
+from matplotlib import patches
 
 import util_eddies
 
@@ -42,17 +43,46 @@ def plot_single_traj(
     annotate_flag,
     color,
     color_initial,
+    arrows,
 ):
     x, y = get_extr_coord(traj, e_overestim, SHPC, orientation)
-    ax.plot(x, y, color, linewidth=0.5, transform=src_crs)
-    ax.plot(
-        x[0],
-        y[0],
-        marker="s",
-        markersize=2,
-        color=color_initial,
-        transform=src_crs,
-    )
+
+    if arrows:
+        # Markers at eatch point and arrows between points, all in the
+        # same color
+
+        ax.plot(
+            x,
+            y,
+            marker="o",
+            linestyle="",
+            markersize=2,
+            color=color,
+            transform=src_crs,
+        )
+
+        # We do not use quiver because it does not work easily with a
+        # projection and angles="xy", scale_units="xy", scale=1.
+        for i in range(len(x) - 1):
+            # Do not use argument transform of FancyArrowPatch because
+            # it does not work with ccrs.Geodetic().
+            posA = ax.projection.transform_point(x[i], y[i], src_crs)
+            posB = ax.projection.transform_point(x[i + 1], y[i + 1], src_crs)
+            arrow = patches.FancyArrowPatch(
+                posA, posB, arrowstyle="-|>", color=color, mutation_scale=10
+            )
+            ax.add_patch(arrow)
+    else:
+        # Marker at the initial point only, with a different color, no arrows
+        ax.plot(x, y, color, linewidth=0.5, transform=src_crs)
+        ax.plot(
+            x[0],
+            y[0],
+            marker="s",
+            markersize=2,
+            color=color_initial,
+            transform=src_crs,
+        )
 
     if annotate_flag:
         ax.annotate(
@@ -150,6 +180,7 @@ if __name__ == "__main__":
                     args.annotate,
                     color="red",
                     color_initial="green",
+                    arrows=False,
                 )
                 break
         else:
@@ -165,6 +196,7 @@ if __name__ == "__main__":
             args.annotate,
             color="red",
             color_initial="green",
+            arrows=False,
         )
     else:
         if args.alt:
@@ -202,6 +234,7 @@ if __name__ == "__main__":
                     args.annotate,
                     color,
                     color_initial,
+                    arrows=False,
                 )
         else:
             # args.min_duration > 1
@@ -227,6 +260,7 @@ if __name__ == "__main__":
                         args.annotate,
                         color,
                         color_initial,
+                        arrows=False,
                     )
 
             print(