Re: [ros-users] costmap_2d questions

Jack,

Here's how I use the messages... though its not an official standard and I
expect others may do things differently.

OccupancyGrid: Used for sending maps over ROS. I only use this message for
sending occupancy grids from SLAM systems or something like the map_server.

GridCells: Meant for visualization, though some people have started using
them for other things. I use them when I want rviz or another visualization
tool to be able to display information about certain cells in a 2D grid.

PointCloud: I use this type for publishing sensor data or filtered sensor
data.... though this message is used throughout the ROS ecosystem for a
variety of different reasons. In the navigation stack at least, a PointCloud
typically refers to some observation about obstacles in the world made by a
sensor.

Hope this helps,

Eitan

On Tue, Sep 21, 2010 at 2:51 PM, Jack O'Quin <jack.oquin@gmail.com> wrote:

> On Tue, Sep 21, 2010 at 4:06 PM, Eric Perko <wisesage5001@gmail.com>
> wrote:
>
> > On Tue, Sep 21, 2010 at 3:01 PM, Jack O'Quin <jack.oquin@gmail.com>
> wrote:
> >>
> >> Has there been any consideration of accepting nav_msgs/OccupancyGrid
> >> or nav_msgs/GridCells as input?
> >
> > We're actually working on a node to turn OccupancyGrid messages into
> > PointClouds, which are then fed into the costmap. Once we get it
> finished,
> > tested and some usage documentation done, we'll be sharing it.
>
> Thanks.
>
> I don't have any immediate need for it. Mainly, I am trying to
> understand the larger picture of how the occupancy grid fits into the
> whole system. A large O-grid is hard to share over TCP connections
> (except infrequently). PointClouds tend to get big, too. Nodelets seem
> to offer higher bandwidth in certain useful cases, but not all.
>
> I am still somewhat confused about how these various messages are
> intended to be used in combination. When would we publish an
> OccupancyGrid versus GridCells or PointCloud?
> --
> joq
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