Play around with the invisibleForTooLong parameter.

Reduce the number of frames that an ant can be invisible before its
track is deleted, to reduce the length of tracks that go off frame.
This led to mild success! The pipeline now accurately tracks 16 of the 17
ants that actually cross the bridge. (see #18 for more details)

ant_tracking.m

@@ -198,16 +198,17 @@ function deleteLostTracks()
         return;
     end
 
-    invisibleForTooLong = 20;
+    invisibleForTooLong = 4;
     ageThreshold = 8;
+    visibilityThreshold = 0.6;
 
     % Compute the fraction of the track's age for which it was visible.
     ages = [tracks(:).age];
     totalVisibleCounts = [tracks(:).totalVisibleCount];
     visibility = totalVisibleCounts ./ ages;
 
     % Find the indices of 'lost' tracks.
-    lostInds = (ages < ageThreshold & visibility < 0.6) | ...
+    lostInds = (ages < ageThreshold & visibility < visibilityThreshold) | ...
         [tracks(:).consecutiveInvisibleCount] >= invisibleForTooLong;
 
     % Delete lost tracks.