| ROS Resources: Documentation | Support | Discussion Forum | Index | Service Status | ros @ Robotics Stack Exchange |
Hi everyone, I have a topic name called /twist_cmd from autoware twist_filter. But the mavros needs the topic /cmd_vel.
/cmd_vel is geometry_msgs/Twist.msg but /twist_cmd is geometry_msgs/TwistStamped.msg
how to change geometry_msgs/TwistStamped.msg to /cmd_vel is geometry_msgs/Twist.msg
Please help me,Thank you!
Most of the time when you see the ros message types with additional stamped extension , that means in i addition to original message type there is also std_msgs::Header included together as one comapct message. In your case , the geometry_msgs::TwistStaped have original original geometry_msgs::Twist and std_msgs::Header. If you you can extract the only twist with for example something like this ; in your callback ;
geometry_msgs::Twist your_extarcted_twist = Msg->twist ;
While this does get you the data, it's important to recognise the different semantics between Twist and TwistStamped. The former is a bare twist (ie: set of linear and angular velocities), while the latter is a twist, but in a certain coordinate system.
Whether that could cause problems for the OP we can't say, but if mavros assumes Twists to be relative to a certain "default" coordinate system, while the TwistStamped is in another, taking just the Twist and disregarding the frame_id could lead to undesirable (and unexpected) results.
Do i need to write another subscriber or publisher ? or just add
;geometry_msgs::Twist your_extarcted_twist = Msg->twist
in my node?
Thanks for the completion, I think since he just needs bare twist , I would interpret this as the coordinate system that this twist should be at is predetermined. One thing may Be noted further is that , the op should make sure that the source twiststamped message is streamed from this very same coordinate system.
@louis960126, depends on what you want to do with this new acquired twist message, probably you will need to write a publisher and publish it with appropriate topic name
You don't need to write a node. Look into topic_tools, either transform or relay_field.
I found this in topic_tools , I will try it tomorrow. just subscribe and pub right? Thank you sir!
rosrun topic_tools transform /twist_cmd /cmd_vel geometry_msgs/Twist
something error
too few arguments
I finished this node, thx for your help. have a nice day!
If you don't care about transforming the velocities to the correct frame (see my comment under @atas' answer), then the following should do what you want:
rosrun topic_tools transform /twist_cmd /cmd_vel geometry_msgs/Twist 'm.twist'
This takes the twist field from the messages which come in on the input topic, and publishes just that field as a new message on the output topic. Adjust as necessary of course.
No need to write your own node, as I mentioned earlier.
Refer to wiki/topic_tools - transform for more information about transform.
Asked: 2020-04-10 07:59:04 -0600
Seen: 12,110 times
Last updated: Apr 13 '20
ROS Answers is licensed under Creative Commons Attribution 3.0 Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.