Sequential number does NOT increase in rosbag

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Hi,

I am using an Erratic robot equipped with a Hokuyo laser sensor. The first thing I want to do is to get a map by gmapping. I did it in this way:

** Open a few terminals, set the simulated time and then start roscore

** roslaunch erratic_player erratic_base.launch

** rosrun hokuyo_node hokuyo_node

** rosrun erratic_teleop erratic_keyboard_teleop

** rosbag record -O mylaserdata /scan /tf

After the recording finished, I close all of the above except roscore, start the gmapping, and then play the bag by:

** rosbag play --clock mylaserdata.bag

I got nothing but a warning:

warning: [1315017585.310852253, 1315016815.179267613]: MessageFilter [target=/odom ]: Dropped 100.00% of messages so far. Please turn the [ros.gmapping.message_notifier] rosconsole logger to DEBUG for more information.

I checked by the rxconsole, and found something like the following repeatedly.

MessageFilter [target=/odom ]: Added message in frame /base_laser at time 1315016811.038, count now 5

MessageFilter [target=/odom ]: Removed oldest message because buffer is full, count now 5 (frame_id=/base_laser, stamp=1315016810.938059)

I believe there are some reason making the new-coming range information not instantly accepted. So I checked the messages from topics of /tf and /scan. I compared them with the messages from the downloaded bag, and found the "seq" number from /tf does not increase at all: always 0. I guess the reason that the laser readings are over buffered is just this number not increasing.

I am new to the ROS community. Could anyone kindly tell me how to force the "seq" number growing?

Thanks in advance.

Shiqi Zhang