[ros-users] Moving frames in 3D (6dof)

Augusto Luis Ballardini aballardini at tiscali.it
Wed May 11 04:51:00 UTC 2011

Hi everybody, I have a question about frames , transforms and TF. I would
like to extend the simples Turtle tf tutorials (
http://www.ros.org/wiki/tf/Tutorials) based on a 2D space but I'm having a
lot of troubles doing it. Unfortunately I didn't find (yet) something on the
mailing list or on ros-answers...
I have this 3 frames:

   - world_frame
   - odom_frame (with a fixed transform respect to world)
   - cart_frame (I move this frame with the odometry data

Here is the code:

static tf::TransformBroadcaster br;
> static tf::TransformListener tf_;

and this

while (ros::ok()){

> transform.setOrigin(tf::Vector3(3,3,0));
> transform.setRotation(tf::createQuaternionFromRPY(0.0,0.0,0.0));
> br.sendTransform(tf::StampedTransform(transform, ros::Time::now(),
> "/world", "/odom"));

here, with updateOdom I calculate the x,y,theta position from the odometry
(like the tutorial<https://code.ros.org/svn/ros-pkg/branches/trunk_cturtle/stacks/ros_pkg_tutorials/turtle_tf/src/turtle_tf_broadcaster.cpp>

> updateOdom(1);





 br.sendTransform(tf::StampedTransform(transform, ros::Time::now(), "/odom",
> "/cart_frame"));

}  catch(tf::TransformException e)

{ ROS_WARN("errore transformpose (%s)", e.what()); }

Now what I'm trying to do is move the cart_frame not only with the x+y+th
params but with a full 6-dof transform, as if the the cart_frame was moving
on a circular garage car ramp, and here starts my question: the simplest way
is to add the information to the odometry, so I can call the sendtransform()
directly, but what if I had a situation where the odometer always sends only
2D transforms?
In the example I tried to send a transform with a small pitch at the
beginning of the while (ros ok())

> transform.setRotation(tf::createQuaternionFromRPY(0.0,0.4,0.0));
> br.sendTransform(tf::StampedTransform(transform, ros::Time::now(),
> "/world", "/odom"));

and this is the outcome http://www.youtube.com/watch?v=d4ktwwukCV0, not
properly what I want...

Ok, probably  I am very tired and confused today but if someone can tell me
where I'm wrong I'll be infinitely grateful =)
Thank you

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