tf error: could not find connection between world and odom...

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Hello,

I am trying to make hector quadrotor use viso2_ros ,, after having configured correctly ( mono_odometer of viso2_ros takes in image from front_cam of hector) , I got warning that viso2_ros couldn't find the mapping base_link to front_cam_optical_frame and in the rviz of hector simulation, when I tried to add show pose parameter , it outputted 'couldn't find connection between world and odom...'

ok now I checked using tf view_frames

and this is what I got

ok maybe it was because of the lack of link between base_link and fornt_cam_optical_frame,,

I linked both using some code

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

  int main(int argc, char** argv){
 ros::init(argc, argv, "hector_remapping_tf");
 ros::NodeHandle n;

ros::Rate r(100);

 tf::TransformBroadcaster broadcaster;

 while(n.ok()){
   broadcaster.sendTransform(
     tf::StampedTransform(
       tf::Transform(tf::Quaternion(0, 0, 0, 1), tf::Vector3(0.0, 0.0, -0.2)),
       ros::Time::now(),"base_link", "front_cam_optical_frame"));
   r.sleep();
 }
}

now the warning of lack of base_link to front_cam_optical_frame was gone but still the world and odom frame are not linked (checked using tf view_frames and rviz)