Merge pull request #675 from dstl/zero_track_plot_fix

Fix Plotter raising error when no tracks available to plot

stonesoup/plotter.py

@@ -276,9 +276,10 @@ def plot_tracks(self, tracks, mapping, uncertainty=False, particle=False, track_
                 continue
             track_colors[track] = plt.getp(line[0], 'color')
 
-        # Assuming a single track or all plotted as the same colour then the following will work.
-        # Otherwise will just render the final track colour.
-        tracks_kwargs['color'] = plt.getp(line[0], 'color')
+        if tracks:  # If no tracks `line` won't be defined
+            # Assuming a single track or all plotted as the same colour then the following will
+            # work. Otherwise will just render the final track colour.
+            tracks_kwargs['color'] = plt.getp(line[0], 'color')
 
         # Generate legend items for track
         track_handle = Line2D([], [], linestyle=tracks_kwargs['linestyle'],

stonesoup/tests/test_plotter.py

@@ -122,3 +122,8 @@ def test_plot_sensors():
     plotter3d.plot_sensors(sensor, marker='o', color='red')
     plt.close()
     assert 'Sensor' in plotter3d.legend_dict
+
+
+def test_empty_tracks():
+    plotter.plot_tracks(set(), [0, 2])
+    plt.close()