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Read Data

Play back data from log file

Since R2019b

  • Read Data block

ROS Toolbox / ROS


The Read Data block plays back rosbag logfiles by outputting the most recent message from the log file based on the current simulation time. You must load a rosbag log file (.bag) and specify the Topic in the block mask to get a stream of messages from the file. Messages on this topic are output from the file in sync with the simulation time.

In the Read Data block mask, click Load log file data to specify a rosbag log file (.bag) to load. In the Load Log File window, specify a Start time offset, in seconds, to start playback at a certain point in the file. Duration specifies how long the block should play back this file in seconds. By default, the block outputs all messages for the specific Topic in the file.



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New message indicator, returned as a logical. If the output is 1, then a new message was loaded from the rosbag file at that time. This output can be used to trigger subsystems for processing new messages received.

ROS message, returned as a nonvirtual bus. Messages are output in the order they are stored in the rosbag and synced with the simulation time.

Data Types: bus


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Topic name to extract from log file, specified as a string. This topic must exist in the loaded rosbag. Click the Load rosbag file Use Select ... to inspect the topics available and select a specific topic.

Interval between outputs, specified as a scalar. In simulation, the sample time follows simulation time and not actual wall-clock time.

This default value indicates that the block sample time is inherited.

For more information about the inherited sample time type, see Specify Sample Time (Simulink).

Version History

Introduced in R2019b