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Losing TFs

asked 2012-10-31 02:36:24 -0500

narcispr gravatar image

updated 2014-01-28 17:14:07 -0500

ngrennan gravatar image

Here is my problem with TFs:

  • I have a node publishing a topic and its related TF:

    pose_tf = tf.TransformBroadcaster()
    o = tf.transformations.quaternion_from_euler(roll, pitch, yaw, 'sxyz')
    pose_tf.sendTransform((pose_x, pose_y, pose_z), o, topic.header.stamp, topic.header.frame_id, main_frame)
    self.pub.publish(topic)

  • From another node, I subscribe to this topic using

    rospy.Subscriber("/topic_name", TopicType, self.function)

  • Each time this node receives a /topic_name, function self.function is executed. To obtain the TF relating the main_frame and the topic_frame I use:

try:
    (trans, rot) = self.listener.lookupTransform( main_frame, topic.header.frame_id, topic.header.stamp)
except (tf.LookupException, tf.ConnectivityException, tf.ExtrapolationException):
    rospy.logerr('Define TF for the topic!)

  • For the first messages the lookupTransform function always generates an exception. After 1 second it starts working properly. I've tried adding a waitForTransform but I've the same problem.

self.listener.waitForTransform(main_frame, topic.header.frame_id, rospy.Time(), rospy.Duration(4.0))

Is it correct to put in the lookupTransform the time topic.header.stamp instead of rospy.Time(0)? (I d'ont want the last TF but the one published in this moment). Am I using function waitForTransform correctly? Any idea?

I'm using Ubuntu 12.04 and ros fuerte. Thank you!

UPDATE: If I add the waitForTransform call inside the try-exception block I can see the following (where line 277 corresponds to self.listener.waitForTransform(main_frame, topic.header.frame_id, rospy.Time(), rospy.Duration(1.0))):

bad callback: <bound method="" poseekfslam.landmarkupdate="" of="" <__main__.poseekfslam="" instance="" at="" 0xab3f6cc="">> Traceback (most recent call last): File "/opt/ros/fuerte/lib/python2.7/dist-packages/rospy/topics.py", line 678, in _invoke_callback cb(msg) File "/home/narcis/workspace/cola2/pose_ekf_slam/src/pose_ekf_slam.py", line 277, in landmarkUpdate rospy.Duration(1.0)) Exception

Seems that waitForTransform or maybe rospy.Duration(1.0) are generating and exception.

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Comments

Which exception do you get?

Lorenz gravatar imageLorenz ( 2012-10-31 02:40:24 -0500 )edit

Unable to lookup transform, cache is empty, when looking up transform from frame "frame_name"

narcispr gravatar imagenarcispr ( 2012-10-31 02:45:34 -0500 )edit

Could you maybe post the source code that is causing the error? The callback seems to raise an error somewhere and it would be interesting what the exception is.

Lorenz gravatar imageLorenz ( 2012-10-31 23:26:37 -0500 )edit

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answered 2012-10-31 03:02:01 -0500

Lorenz gravatar image

Your code looks correct. It just takes a while until the TF tree evolves completely and that's where your error within the first second probably comes from. I think it is definitely possible to get exceptions during that time. However, I don't feel like waitForTransform should really throw an exception here. I'm not sure if this is a bug or an actual design decision but you might want to consider filing a ticket at the corresponding bug tracker.

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Asked: 2012-10-31 02:36:24 -0500

Seen: 358 times

Last updated: Oct 31 '12