It sounds like whatever sensor you're using to provide obstacle information to the navigation stack continuously sees an obstacle right in front of the robot. The obstacle isn't actually there, but the sensor is reporting that it is. Can you look at just the raw data from your sensor in rviz (with a laser that'd be the raw LaserScan)? I imagine that you'll see a point in front of the robot. For the navigation stack to work, you'll have to resolve this issue with your sensor.

Eitan

On Wed, Sep 29, 2010 at 3:39 AM, safdar_zaman <safdaraslam@yahoo.com> wrote:

Hi Eitan,
Thanks for the Reply.
I again checked it now. The Robot keeps moving backwards. Initially when I
set the pose it sees some obstacle before it. Also inflated obstacles
surrounded by Blue color. When I press 2D Nav Goal button of rviz and click
it in the map a little forward from the Robot, then Robot does not move
forward instead starts moving backwards. I observer the topics in rviz that
While moving backwards the obstacles it sees before it, slowly disappear and
new obstacles become inflated before it.
But it always slowly move backwards and I had to switch it off.

Any idea please?

I dont know where the topic /unknown_space is because I did not subscribed
it. I am following the tutorials
for SetUp http://www.ros.org/wiki/navigation/Tutorials/RobotSetup and for
Goal
http://www.ros.org/wiki/navigation/Tutorials/Using%20rviz%20with%20the%20Navigation%20Stack

thanks in advance.
regards

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