Read Data

Play back data from log file

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Libraries:
ROS Toolbox / ROS

Description

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.

Examples

Play Back Data from Jackal rosbag Logfile in Simulink

Use the Read Data block to play back data from a rosbag log file recorded from a Jackal™ robot from ClearPath™ Robotics.

• Open Live Script

Ports

Output

IsNew — New message indicator

0 | 1

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.

Msg — ROS message

nonvirtual bus

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

Parameters

Topic — Topic name to extract from log file

string

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.

Sample time — Interval between outputs

–1 (default) | scalar

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