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seeking in a bag file

I am going to work with large bag files, offline. I am going to have to seek back and forth in the bag to find the data I need, i.e. some sort of random access. Before I start working on a hack of my own, I'd like to know if there is any standard approach implemented out there. Let say the goal is to be able to retrieve a message on topic X, at or near time T.

I am thinking that I could open a new View with the proper query (X,T). But I am wondering how long will it take. i.e. when opening a view, is it reading an index to open it in a constant time, or is it going to scan through the bag until it finds it?

seeking in a bag file

I am going to work with large bag files, offline. I am going to have to seek back and forth in the bag to find the data I need, i.e. some sort of random access. Before I start working on a hack of my own, I'd like to know if there is any standard approach implemented out there. Let say the goal is to be able to retrieve a message on topic X, at or near time T.

Note: this question is related: http://answers.ros.org/question/10852/playing-back-large-files-with-rosbag/

I am thinking that I could open a new View with the proper query (X,T). But I am wondering how long will it take. i.e. when opening a view, is it reading an index to open it in a constant time, or is it going to scan through the bag until it finds it?