[ros-users] Wifi communication getting slow

[Steven Bellens]

2011/1/5 Brian Gerkey <gerkey at willowgarage.com>:
> On Wed, Jan 5, 2011 at 8:37 AM, Steven Bellens
> <steven.bellens at mech.kuleuven.be> wrote:
>
>> I've figured out the problem occurs the moment I start running the
>> navigation stack. I've been able to build a map using gmapping
>> (running the gmapping mode on the groundstation), and the ping
>> responses were constantly okay. When I start up navigation without a
>> pre-build map (amcl - move base - gmapping), the ping responses
>> suddenly increase (from 2 - 8 ms to 1000+ ms). When I try the same
>> with a static map, everything goes well. Am I doing something wrong in
>> this setup, e.g. can I run amcl and gmapping at the same time? If not,
>> how should I run the navigation stack without a prebuild map?
>
> You should not run amcl and gmapping simultaneously.  They're both
> estimating the map->odom transform, and you only want one source of
> that information.  If you want to run without an a priori map, you
> should use only gmapping, not amcl.  If you save the map produced by
> gmapping (e.g., using the map_server/map_saver tool), you can then
> localize against that map with amcl, and not run gmapping.
>
> But the gmapping / amcl transform conflict shouldn't cause network
> latency.  Instead, I would suspect that it's the bandwidth being
> consumed by sending the updated map from gmapping to move_base;
> move_base subscribes to the map, which gmapping publishes as a latched
> topic.  Maps can be big, and the map produced by gmapping is
> automatically something like 4000x4000 cells, regardless of how much
> space has actually been observed by the robot (there's an opportunity
> to optimize gmapping's behavior, to be sure).  An experiment to try:
> increase the gmapping/map_update_interval parameter.  Then the map
> will be published less often, and soak up less bandwidth.  The
> tradeoff, of course, is that move_base will receive updated maps less
> frequently.

When running all except the hokuyo_node on the groundstation (no
gmapping, only amcl), the network traffic is still about 8MB / s from
the robot to the ground  station. I didn't check which nodes are the
main consumers here yet, but the /scan topic only takes around 20kB /
s of this. This 8 MB / s is way too much as only laser scan data needs
to be send, right?
The ROS master is running on the groundstation.

>
>> Another problem I face is about the navigation: the holonomic robot
>> localizes itself OK, but the goals I send with rviz only manage to let
>> it rotate (there is never a translational velocity command), so the
>> robot starts rotating, but never gets anywhere close where I want him
>> to go :). Any ideas on that?
>
> This is probably caused by the tf conflict between amcl and gmapping.
> When you bring up the navigation stack on top of gmapping, don't run
> amcl.

This also happens when only running amcl. I found this to be a problem
of the map origin coordinates or something related, but might need
some help solving it. I've build a map using gmapping and saved it
with the map_saver functionality. The map.yaml file places the origin
of the map at [-50.0 , -50.0, 0.0], which is in the middle of the map.
However the costmap always complains:

[ WARN] [1294326503.260648549]: The origin for the sensor at (-0.97,
0.16, 0.00) is out of map bounds. So, the costmap cannot raytrace for
it.

As the map building goes fine, I expect the tf frames to be OK (there
are no errors displayed). Do I need some more transformations to get
the sensor frame updated with this map origin values?

Steven

>
>        brian.
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