unknown_cost_value

edit

For the future visitors,

I was trying to prohibit the unknown space from planners to plan through, and nothing helped but this parameter in my case.

Basically after setting GlobalPlanner/allow_unknown to false and track_unknown_space: true for costmap layers, the expected behaviour was avoiding the unknown spaces while planning. But it didn't work without setting these parameters for costmaps:

global_costmap:
  unknown_cost_value: 254
  ...
local_costmap:
  unknown_cost_value: 254
  ...

Even though the question was ambiguous, I hope people will find this explanation after googling queries like "setting GlobalPlanner allow_unknown` parameter doesn't work".