[ros-users] Confusion with TF...

[John Hsu]

Hi Jason
Can you pose the nodes that are publishing the necessary tf transforms as
well?
thanks,
John

On Wed, Apr 14, 2010 at 2:37 PM, Jason Owens <jlowens at gmail.com> wrote:

> On Wed, Apr 14, 2010 at 2:18 PM, John Hsu <johnhsu at willowgarage.com>
> wrote:
> > Hi,
> > It's hard to debug this issue without being able to reproduce the
> problem...
>
> I figured that might be the case...
>
> > is there a way you can create a pseudo-package which we can run and
> > reproduce the symptoms?  Also, can you also attach outputs from
> >
> > rosrun tf view_frames
> > roswtf
>
> I'll work on creating a mini-pkg; until then, I've uploaded two bag
> files at http://public.me.com/robocoder (the jitter has the matching
> tf rate 10Hz, and the no_jitter has 13Hz), and I've attached the
> frames and wtf output to this message. I do notice that for some
> reason, the frame.pdf shows the messages as being quite old - is this
> something that has to do with gazebo? When I look at the
> ros::Time::toSec() when the system is running, I get values that match
> the ROS time displayed in rviz, i.e. starting from 0.
>
> Thanks for looking at this!
> -Jason
>
> >
> > You can see most of the tf debugging tools at:
> >
> > http://www.ros.org/wiki/tf/Debugging%20tools
> >
> > Lastly, there's a tf troubleshoot page here that might be helpful:
> >
> > http://www.ros.org/wiki/tf/Troubleshooting
> >
> > thanks,
> > John
> >
> > On Wed, Apr 14, 2010 at 6:30 AM, Jason Owens <jlowens at gmail.com> wrote:
> >>
> >> Hello all,
> >>
> >> I've been having some issues with tf, time and gazebo... quite
> >> possibly due to a case of newbie-itis. Perhaps the simplest question
> >> is this:
> >>
> >> Why would changing the update rate of the gazebo_ros_p3d plugin from
> >> 10Hz -> 11Hz make the laser scans bounce all over the place when
> >> moving the robot?
> >>
> >> I am confused as to why increasing the data rate of the pose transform
> >> would cause the laser scans (both sensor frame and transformed world
> >> frame point cloud) to jitter so much. I feel like this is an issue,
> >> since when I implement SLAM on board a real robot, I will not be able
> >> to have great control over the data publish rate, which other nodes
> >> may depend on (e.g. an incremental generalized voronoi graph builder).
> >>
> >> A little more background:
> >>
> >> Given a create-like simulated robot with differential drive,
> >> hokuyo-like laser, the gazebo-ros-p3d plugin publishing ground-truth
> >> pose, another node publishing the /world -> /base_link transform based
> >> on this pose info, and a node that builds an occupancy grid -
> >> everything works quite well (i.e. rviz shows the map and laser data
> >> "cleanly"). This is when the updateRate of the p3d plugin is set to
> >> some multiple of 10Hz (which is the rate of the laser). However, if I
> >> perturb the updateRate of the ground truth (i.e. 13Hz, 15Hz, 19Hz),
> >> the laser scans start to jump around quite a bit in rviz, and the
> >> occupancy grid gets very messy. I realize a real robot will not have a
> >> perfectly clean map, but I am trying to understand the problem with
> >> the transforms here so I can mitigate it.
> >>
> >> I *am* using tf::MessageFilter, and have tried a variety of queue
> >> sizes and tolerances, but to no avail. I actually first noticed the
> >> problem when running on a laptop with 2 instead of 4 cores (like my
> >> desktop), and it was clear not all the messages were being received.
> >> roswtf doesn't show anything of interest (other than the /time topics
> >> are unconnected, which I assume is due to "/use_sim_time = true"?). I
> >> thought it was due to extrapolation, but it seems extrapolation is
> >> disabled by default. However, if I print the extrapolation_mode from
> >> the time_cache I get *a lot* of extrapolate_forward cases... which I
> >> thought the tf::MessageFilter would prevent.
> >>
> >> I have attached a copy of my urdf and launch file, if they may help.
> >>
> >> Thanks ahead for any suggestions! Also - thank you so much for ROS; so
> >> far, it has made my life easier in many ways, and hopefully I'll be
> >> able to convince my employer (DoD) to allow us to contribute our
> >> source back to the community.
> >>
> >> -Jason
> >>
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> >>
> >
> >
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