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tf::Transform getOrigin returning different value from rviz

asked 2018-08-15 20:10:47 -0500

FelipeNascimento gravatar image

Hi there!

I'm trying to see the pose and rotation from a UR5 using tf and comparing with rviz and the robot GUI itself. In rviz I get the same result as the GUI, but when I try to listen to the transform and see the values, and the values are different from expected.

#include <ros/ros.h>
#include <iostream>

//tf
#include <tf/transform_broadcaster.h>
#include <tf/transform_listener.h>

int main(int argc, char** argcv){
    ros::init(argc, argcv, "world_to_robot_pose");

    tf::StampedTransform transform;

    static tf::TransformListener listener;

    while(ros::ok()){

        try{
            listener.lookupTransform("/tool0_controller","/world",ros::Time(0), transform);
            ROS_INFO_STREAM(" Transform: " << transform.getOrigin().x() << ", " << transform.getOrigin().y() << ", " <<transform.getOrigin().z() << ", " << transform.getRotation().x() << ", " << transform.getRotation().y() << ", " << transform.getRotation().z());
        }
        catch (tf::TransformException &ex) {
             ROS_ERROR("%s",ex.what());
             ros::Duration(1.0).sleep();
        }

        ros::spinOnce();
    }
    return 0;
}

The program returns me this transformation:

Transform: -0.131564, 0.80858, -0.20301, 0.640242, -0.279677, -0.16726

and in rviz: Absolute Position and Orientation: 0.61686, 0.10287, 0.57003, -0.64024, 0.27968, 0.16726

My question is, is it supposed to be different? The Relative Position in Rviz is the same as the robot GUI.

Thanks in advance.

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Comments

Afaik, only the base->tool0_controller transform should correspond to what the Polyscope UI shows (or at least, if you configure it to show you poses relative to its base frame). The base_link (and world) are 180 degrees rotated over Z compared to the controller's coordinate system.

gvdhoorn gravatar image gvdhoorn  ( 2018-08-16 02:44:25 -0500 )edit

The two transforms appear to the inverse of each other. Is this a confusion between the pose of the origin of frame X described in frame Y and the transform from frame Y to frame X?

PeteBlackerThe3rd gravatar image PeteBlackerThe3rd  ( 2018-08-16 04:51:13 -0500 )edit

I noticed the 180 degrees rotation from world->base as @gvdhoorn said, but just now I noticed that the Euclidean norm is the same for the two transforms, so it might be just as @PeteBlackerThe3rd said. I'll have to make tests to see if that makes any difference in relation to other tfs and moveit

FelipeNascimento gravatar image FelipeNascimento  ( 2018-08-16 10:50:26 -0500 )edit

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answered 2018-09-04 15:49:11 -0500

FelipeNascimento gravatar image

For some reason, the code gave me the correct transform when I changed the direction of the transform:

listener.lookupTransform("/world","/tool0_controller",ros::Time(0), transform);

which is different from the tf tutorials.

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answered 2018-09-10 09:20:15 -0500

This could be a confusion of concepts. The pose of the origin of frame X described in frame Y is the inverse of the transform from frame X to frame Y.

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Asked: 2018-08-15 20:10:47 -0500

Seen: 1,471 times

Last updated: Sep 04 '18