Frame id /base_link does not exist! when extracting .bag to .pcd

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Hello guys,

I'm pretty new on the ROS system and I'm having some trouble when trying to convert de pointcloud in the .bag file to an external .pcd file.

Soooo what I did is the following:

-Open a first terminal raphael@ubuntu:~/Link_to_HESB/Bachelor/low_freq$ roscore The location is where my .bag files are.

Then I opend a second terminal: raphael@ubuntu:~/Link_to_HESB/Bachelor/low_freq$ rosbag info 2012-08-10-17-32-31.bag

*path: 2012-08-10-17-32-31.bag version:
2.0 duration: 3:52s (232s) start: Aug 10 2012 22:32:31.20 (1344630751.20) end: Aug 10 2012 22:36:24.18 (1344630984.18) size: 4.8 GB messages: 9127 compression: none [2326/2326 chunks] types: bond/Status [eacc84bf5d65b6777d4c50f463dfb9c8] diagnostic_msgs/DiagnosticArray [3cfbeff055e708a24c3d946a5c8139cd] rosgraph_msgs/Log [acffd30cd6b6de30f120938c17c593fb] sensor_msgs/PointCloud2 [1158d486dd51d683ce2f1be655c3c181] std_msgs/String [992ce8a1687cec8c8bd883ec73ca41d1] velodyne_msgs/VelodyneScan [50804fc9533a0e579e6322c04ae70566] topics: /diagnostics 232 msgs : diagnostic_msgs/DiagnosticArray /rosout 49 msgs : rosgraph_msgs/Log (4 connections) /septentrio/SbfAttCovEuler_1_0 233 msgs : std_msgs/String

        /septentrio/SbfAttEuler_1_0             233 msgs    : std_msgs/String       

        /septentrio/SbfBaseLine_1_0             233 msgs    : std_msgs/String       

        /septentrio/SbfBaseVectorGeod_1_0       233 msgs    : std_msgs/String       

        /septentrio/SbfDOP_2                  233 msgs    : std_msgs/String       

        /septentrio/SbfEndOfAtt_1_0             233 msgs    : std_msgs/String       

        /septentrio/SbfEndOfPVT_1_0             233 msgs    : std_msgs/String       

        /septentrio/SbfGeoCorrections_1_0       233 msgs    : std_msgs/String       

        /septentrio/SbfPVTGeodetic_2_1          233 msgs    : std_msgs/String       

        /septentrio/SbfPVTResiduals_2_1         233 msgs    : std_msgs/String       

        /septentrio/SbfPosCovGeodetic_1_0       233 msgs    : std_msgs/String       

        /septentrio/SbfPvtSatCartesian_1_0      233 msgs    : std_msgs/String       

        /septentrio/SbfRAIMStatistics_2_0       233 msgs    : std_msgs/String       

        /septentrio/SbfVelCovGeodetic_1_0       233 msgs    : std_msgs/String       

        /velodyne_nodelet_manager/bond          932 msgs    : bond/Status               (3 connections)
        /velodyne_packets                    2326 msgs    :    velodyne_msgs/VelodyneScan     
        /velodyne_points                     2326 msgs    :    sensor_msgs/PointCloud2*

Soo then what I do is that I try to extract the /velodyne_points but is doesn't work:

*raphael@ubuntu:~/Link_to_HESB/Bachelor/low_freq$ rosrun pcl_ros bag_to_pcd 2012-08-10-17-32-31.bag /velodyne_points ./pointclouds Saving recorded sensor_msgs::PointCloud2 messages on topic /velodyne_points to ./pointclouds

ERROR 1361880690.779414125: Frame id /base_link does not exist! Frames (1):

Erreur de segmentation (core dumped)*

So I found some informations about changing a TF file but I'm really new on ROS & Ubuntu so I have no clue where & how I actually should do this ;)

Can someone here help me on this? I already lost some hours trying to solve that ;)