Difference between Costmap2D and OccupancyGrid not clear

Question

Hello

It is not clear to me what the difference between costmap2d and OccupancyGrid is.

From what I learned in Tutorials, OccupancyGrid will be formed using gmapping and it will have three values: 0 for free space, 100 for obstacle, and -1 for unknown. This map will be used later for navigation.

But in navigation stack, it says that global planner uses costmap2d to make a plan and not the occupancyGrid and that costmap2D has also three values for free, occupied and unknown.

So, may questions are: 1- What is the difference between Costmap2D and OccupancyGrid 2- How to convert from one to another and where this is done? 3- Why Global Planner does not use OccupancyGrid, which seems to provide similar information to Costmap2D

Any clarification of these will be appreciated.

Thanks.

Anis

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Originally posted by Anis on ROS Answers with karma: 253 on 2013-04-04

Post score: 4

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Original comments

Comment by joq on 2013-04-05:
I agree that the names are confusing.

Answer 1

nav_msgs/OccupancyGrid is a ROS message. This is a map that can be passed around between tools, namely gmapping/karto, amcl, and move_base.

costmap2d is a ROS package, which offers a costmap generation tool, which in fact is really 2.5D. That is, it does raytracing from sensor data into a 3d-voxel map, but it outputs a 2d costmap. It is mainly used via a C++ api, not the ROS message api. When used over ROS messages, it posts nav_msgs/GridCells on a variety of topics corresponding to obstacles, inflated obstacles, and unknown space.

Now, in the context of global planner, all planners use the C++ costmap2d interface. And thus, the global costmap2d is typically initialized from some map, which is typically received over a latched topic using nav_msgs/OccupancyGrid. The costmap2d then can do things needed for planning, like inflating obstacles or adding sensor data to the costmap if desired/configured as such.

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Originally posted by fergs with karma: 13902 on 2013-04-05

This answer was ACCEPTED on the original site

Post score: 9