[ros-users] Avoiding Collisions between robots

[Brian Gerkey]

On Mon, Dec 27, 2010 at 10:39 AM, Jack O'Quin <jack.oquin at gmail.com> wrote:
> On Mon, Dec 27, 2010 at 11:48 AM, Eitan Marder-Eppstein
> <eitan at willowgarage.com> wrote:
>> On Sat, Dec 25, 2010 at 7:53 PM, <davidbsp at iol.pt> wrote:
>>> I have been making some experiments on ROS together with Stage, using
>>> multiple mobile robots in the same environment.
>>> All robots run the navigation stack. However, sometimes they collide
>>> with each other.
>>
>> So, its true that the navigation stack doesn't do a great job of handling
>> the multi-robot case, but I'd expect you to get reasonable results in Stage
>> as long as the laser mounted on each robot is capable of seeing the body of
>> the other robot. Have you verified that each robot in stage sees the other
>> in its entirety?
>
> This is definitely worth checking.
>
> I had problems migrating simulations to recent versions of stage.
> Although stage is a 2D simulation, they've added some "2.5D" features
> in stage version 3. Objects now have heights, and the laser simulation
> appears to send out a horizontal planar scan at the Z level of the
> laser's position. A laser mounted on top of a simulated robot may "see
> over the top" of another, similar robot.

To echo Jack: all models in Stage (including lasers and robot bases)
have heights.  A sensor will only "see" other models at the same
height.  If you copied from standard Stage .world examples, you
probably have some Pioneer-like robots with SICK-like lasers mounted
on their tops in such a way that a robot's laser only sees other
robots' lasers, not their bases.  This is the correct result for such
a robot configuration; in the real world, the laser planes don't
intersect the robot bases.  If you want to simulate a different
(perhaps less realistic) kind of robot, you can adjust the laser
heights; if you post your .world file (and also any files that are
included by your .world file), we can provide some pointers on what to
modify.

	brian.