ROS Publishers

Before you see the code for simple_mover , it may be helpful to see how ROS Publishers work in C++.

Publishers allow a node to send messages to a topic, so that data from the node can be used in other parts of ROS. In C++, ROS publishers typically have the following definition format, although other parameters and arguments are possible:

ros::Publisher pub1 = n.advertise<message_type>("/topic_name", queue_size);

The pub1 object is a publisher object instantiated from the ros::Publisher class. This object allows you to publish messages by calling the publish() function.

To communicate with ROS master in C++, you need a NodeHandle . The node handle n will fully initialize the node.

The advertise() function is used to communicate with ROS and inform that you want to publish a message on a given topic name.
The "/topic_name" indicates which topic the publisher will be publishing to.

The message_type is the type of message being published on "/topic_name". For example, the string message data type in ROS is std_msgs::String .

The queue_size indicates the number of messages that can be stored in a queue. A publisher can store messages in a queue until the messages can be sent. If the number of messages stored exceeds the size of the queue, the oldest messages are dropped.

Once the publisher object pub1 has been created, as above, a message with the specified data type can be published as follows:

pub1.publish(msg);

For more information about C++ ROS publishers, see the documentation here .

ROS Publishers

Assume that a queued message is typically picked up in an average time of 1/10th of a second with a standard deviation of 1/20th of a second, and your publisher is publishing at a frequency of 10Hz. Of the options below, which would be the best setting for queue_size ?

queue_size=2

queue_size=100

queue_size=0

SOLUTION:

`queue_size=2`

Let's get started with simple_mover !