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hello, in the navigation stack, the publishing odometry part. where those values should come from? 16 double vx = 0.1; 17 double vy = -0.1; 18 double vth = 0.1;
from this code: http://wiki.ros.org/navigation/Tutori...
The paragraph below the breakdown of that line of code states:
Here we'll set some velocities that will cause the "base_link" frame to move in the "odom" frame at a rate of 0.1m/s in the x direction, -0.1m/s in the y direction, and 0.1rad/s in the th direction. This will more or less cause our fake robot to drive in a circle.
Basically the robot will move those amounts with every time step.
nav_msgs/odometry messages take the following form:
# This represents an estimate of a position and velocity in free space.
# The pose in this message should be specified in the coordinate frame given by header.frame_id.
# The twist in this message should be specified in the coordinate frame given by the child_frame_id
Header header
string child_frame_id
geometry_msgs/PoseWithCovariance pose
geometry_msgs/TwistWithCovariance twist
You can find information concerning geometry_msgs here.
In a real situation, a robot driver, like p2os or turtlebot, will extract the position and velocity information (or data from the motor encoders) and will produce the nav_msgs/odometry. If you have built your own robot, you will have to create a node which extracts motor encoder data and publishes the nav_msgs/odometry. Take a look at other robot's driver_nodes for an example.
Absolutely right. Those values are an arbitrary value to demonstrate how to publish a nav_msgs/Odometry message over ROS and a transform using tf for a robot.
I have a Pioneer3-DX robot and the p2os_driver node takes encoder information from the robot and publishes the odom message to ROS.
distance = (left_encoder + right_encoder) / 2.0
theta = (left_encoder - right_encoder) / WHEEL_BASE
X_position = distance * sin(theta) Y_position = distance * cos(theta)
For help, take a look here: http://www.geology.smu.edu/~dpa-www/r...
Asked: 2015-03-24 07:35:31 -0500
Seen: 577 times
Last updated: Mar 25 '15
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