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How to broadcast a permanent transformation in tf (tf2)

asked 2018-06-12 11:14:57 -0600

chillax gravatar image

updated 2018-06-12 16:26:44 -0600

Hi everyone,

Is there a way to broadcast a transformation in tf or tf2 only once, but use that transformation at any point in the future?

I am using tf2 for visual odometry with a drone. I can only start the visual odometry algorithm when the drone is already in the air. Therefore I need the transformation from map -> odom_init (position where the odometry was initialized). Then, I can broadcast the odom_init -> current_position transformation based on the odometry output. Then I can look up the tranformation from map -> current_position.

However this only works if I continuously broadcast both transformations (map -> odom_init and odom_init -> current_position). But since the first transformation does not change over time, I would like to broadcast it only once, and use it for all lookups. Is there a way to do this?

If I only broadcast map -> odom_init once, I get [ERROR]: Lookup would require extrapolation into the past.

EDIT Here is the working code for reference:

#include <geometry_msgs/TransformStamped.h>
#include <tf2_ros/static_transform_broadcaster.h>
#include <tf2_ros/transform_broadcaster.h>
#include <tf2_ros/transform_listener.h>

tf2_ros::Buffer tfBuffer;
static tf2_ros::TransformBroadcaster br;
static tf2_ros::StaticTransformBroadcaster sbr;
geometry_msgs::TransformStamped transformStamped;

// Transformation from map to odom_init
transformStamped.header.stamp = ros::Time::now();
transformStamped.header.frame_id = "map";
transformStamped.child_frame_id = "odom_init";
transformStamped.transform.translation.x = odom_init_pos.pose.position.x;
transformStamped.transform.translation.y = odom_init_pos.pose.position.y;
transformStamped.transform.translation.z = odom_init_pos.pose.position.z;
transformStamped.transform.rotation = odom_init_pos.pose.orientation;

// Transformation from odom_init to drone_vision
transformStamped.header.stamp = ros::Time::now();
transformStamped.header.frame_id = "odom_init";
transformStamped.child_frame_id = "current_position";
transformStamped.transform.translation.x = vo_position.pose.pose.position.x;
transformStamped.transform.translation.y = vo_position.pose.pose.position.y;
transformStamped.transform.translation.z = vo_position.pose.pose.position.z;
transformStamped.transform.rotation = vo_position.pose.pose.orientation;

if (send_vision_estimate) {
  try {
    transformStamped = tfBuffer.lookupTransform("map", "current_position", ros::Time(0));
    vision_pos_ENU.pose.position.x = transformStamped.transform.translation.x;
    vision_pos_ENU.pose.position.y = transformStamped.transform.translation.y;
    vision_pos_ENU.pose.position.z = transformStamped.transform.translation.z;
    vision_pos_ENU.pose.orientation = transformStamped.transform.rotation;


    catch (tf2::TransformException &ex){
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1 Answer

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answered 2018-06-12 11:27:34 -0600

gvdhoorn gravatar image

I would like to broadcast it only once, and use it for all lookups.

wiki/tf2/Tutorials: Writing a tf2 static broadcaster (C++).

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So 'static' is the magic keyword! Thanks for the quick answer.

chillax gravatar image chillax  ( 2018-06-12 16:24:08 -0600 )edit

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Asked: 2018-06-12 11:14:57 -0600

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Last updated: Jun 12 '18