Proper way of subsribing to a costmap_2d OccupancyGrid

asked 2016-04-12 12:16:21 -0500

doisyg
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Hi, I am using the costmap_2d_node to build a local costmap from a Lidar. I can view the local costmap properly in Rviz. What I don't understand is that the topic /costmap of type OccupancyGrid is only published once, no matter how high I set the value of the publish_frequency parameter. I see that there is a /costmap_updates topic of type OccupancyGridUpdate and I guess there is a proper way of subcribing to the local costmap through it but i did not find any information about it. For instance, what mechanism Rviz uses to display the live costmap?

answered 2016-04-14 06:18:36 -0500

doisyg
141 ●8 ●9 ●14

Solved by subscribing to costmap_updates topic, example here: https://github.com/DLu/navigation/blo...

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But I would still be interested to have more information abou the underlying mechanism.

doisyg ( 2016-05-26 07:46:11 -0500 )edit

What do you mean by the underlying mechanism?

David Lu ( 2016-05-26 08:56:10 -0500 )edit

How does Rviz get the full costmap in the first place? And also what is the influence of the publish_frequency parameter since it doesn't seem to have any impact on the /costmap topic.

doisyg ( 2016-05-26 09:24:57 -0500 )edit

Rviz subscribes to both topics (costmap and costmap_updates). publish_frequency changes how frequently it publishes the update topic. There is an (undocumented) parameter called always_send_full_costmap.

David Lu ( 2016-05-26 10:03:44 -0500 )edit

Thanks, i didn't know about the always_send_full_costmap param, it can be very useful. But then what is the difference between publish_frequency and update_frequency? I thought it was update_frequency which was controlling the costmap_updates topic rate.

doisyg ( 2016-05-26 10:33:14 -0500 )edit

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Proper way of subsribing to a costmap_2d OccupancyGrid

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Proper way of subsribing to a costmap_2d OccupancyGrid