Read Data

Play back data from ROS 2 log file

Since R2021b

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Libraries:
ROS Toolbox / ROS 2

Description

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 file in DB3 or MCAP file format 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. If a folder contains multiple ROS 2 bag files, you can also read them using the Read Data block by loading the metadata file with .yaml extension.

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

Examples

Play Back Data from ROS 2 Bag Logfile in Simulink

Use the Read Data block to play back data from a ROS 2 bag file.

Open Live Script

Ports

Output

IsNew — New message indicator

logical scalar

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 file at the corresponding time. This output can be used to trigger subsystems for processing new messages.

Data Types: Boolean

Msg — ROS 2 message

nonvirtual bus

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

Data Types: bus

Parameters

Topic — Topic name to extract from log file

string scalar | character vector

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

Sample time — Interval between outputs

-1 (default) | scalar

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

R2024a: MCAP Storage Format Support

You can now read data from a bag folder containing one or more MCAP files.