# Nav Stack Costmap_2d: obstacle_layer w.r.t. which frame

Hello there,

I have a few quetion regarding the obstacle_layer that is used in costmap_2d for the Navigation Stack. I am unsure about a few parameters like min_obstacle_height and max_obstacle_height. I understand the meaning of these two parameters. However, I really don't know w.r.t. which frame these heights shoult be specified. Is it w.r.t. /map, /odom or /base_link? The same question appears for the parameter "origin_z" in the VoxelCostmapPlugin.

In my example, I am using a robot whose base_link is 6 cm above ground. The /map frame (whose tf is published by AMCL I guess) is on the same height as base_link, although I set /odom to be fully on the ground meaning 6 cm below base_link in z-direction.

Can anyone tell me how the mentioned parameters work exactly? Also, does anyone know if the /map frame should be on the same z-height as /odom or if it's normal that mine appears on the same height as base_link?

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The sensor data is transformed into the global frame of the costmap and then the obstacle height is checked. For a global costmap, this is usually map and for a local costmap this is often odom

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