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Read Data

Play back data from ROS 2 log file

  • Library:
  • ROS Toolbox / ROS 2

  • Read Data ROS 2


The Read Data block plays back ROS 2 bag log files by outputting the most recent message from the log file, based on the current simulation time. You must load a ROS 2 bag log file (.db3) and specify a topic, using the Topic parameter, to get a stream of messages from the file. The block outputs messages of this topic from the file in sync with the simulation time.

In the Read Data block mask, select Load logfile data to specify a ROS 2 bag log file (.db3) to load. In the Load Logfile dialog box, specify the full path to the log file, or select Browse and navigate to the logfile you want to load. To start playback at a certain point in the file, specify a Start time offset, in seconds. To specify how long the block plays back this file, from the specified start time, specify a Duration, in seconds. By default, the block outputs all messages for the specified topic in the file.



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New message indicator, returned as a logical scalar. If the output is 1, then the block loaded a new message from the ROS 2 bag log file at the corresponding time. This output can be used to trigger subsystems for processing new messages.

Data Types: Boolean

ROS 2 message, returned as a nonvirtual bus. Messages are returned in the order they are stored in the ROS 2 bag log file and synced with the simulation time.

Data Types: bus


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Specify the name of the topic to extract from the log file. This topic must exist in the loaded ROS 2 bag log file. Click Select to inspect the available topics and select a specific topic.

Specify the interval between outputs. In simulation, the sample time follows simulation time rather than wall-clock time.

The 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 R2021b