[ros-users] About tf and synchronization

[Rodrigo Baravalle]

Hi!

Here are the lines of code of the callback, when an amcl pose arrives..

I used the same frame_id, but, is the timestamp correct? I used the
same as in the tutorial:
http://www.ros.org/wiki/tf/Tutorials/tf%20and%20Time%20(C%2B%2B)

void MergePC::callback(const geometry_msgs::PoseWithCovarianceStampedPtr& o) {
...
    // Read data from the Camera
    pc_current.header.frame_id = "swissranger";
    dev_->readData(pc_current,pc2_current,image_d_, image_i_,
image_c_, image_d16_);

     // I put 100.0, but is the same if I put 20.0, 3.0, or whatever
     tlistener.waitForTransform("/map", "/swissranger",
                               ros::Time(0), ros::Duration(100.0));

     // pc_current is the point cloud arriving from the camera, so it
has the "swissranger" frame_id
     // here is where it fails..
     tlistener.transformPointCloud("/map", pc_current, pc_tf);
...
}

Thanks in advance!

2010/12/21 Wim Meeussen <meeussen at willowgarage.com>:
>> The problem is that I always get an error message like this:
>>
>> "You requested a transform that is 12.571 miliseconds in the past,
>> but the most recent transform in the tf buffer is 49.194 miliseconds old.
>>  When trying to transform between /swissranger and /map."
>
>> I have already tried with "waitForTransform" between the two frames,
>> but nothing seems to happen. I can see by using "rosrun tf
>> view_frames" that amcl is publishing things in the future: "
>> Broadcaster: /amcl ... Most recent transform: -0.086 sec old ... ".
>
> Based on this information your tf tree looks fine. You are just
> requesting a transformation before that information is in the tf
> buffer.  Calling waitForTransform before you request the actual
> transform should work.  Did you call waitForTransform with the same
> frame id's and timestamp as the actual transform? Could you show the
> few lines of code where you do the tf calls?
>
> Wim
>
>
> --
> --
> Wim Meeussen
> Willow Garage Inc.
> <http://www.willowgarage.com)
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