add script to count events in rosbag

dvs_file_writer/scripts/count_events_in_bag.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python
+
+import rosbag
+import dvs_msgs
+import argparse
+
+parser = argparse.ArgumentParser(description='Count number of events in a rosbag')
+parser.add_argument('--topic', default='/dvs/events')
+parser.add_argument('bag')
+
+args = parser.parse_args()
+
+n_events = 0
+
+for topic, msg, t in rosbag.Bag(args.bag).read_messages():
+    # This also replaces tf timestamps under the assumption 
+    # that all transforms in the message share the same timestamp
+    if topic == args.topic:
+        n_events += len(msg.events)
+        print "# events: ", n_events
+