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occupancy_maps.md

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Occupancy maps

An occupancy map is a two-dimensional numpy array representation of a scene in TDW. Each element in the array is an area of a given size and can have one of three values:

Value Meaning
-1 The cell is out of bounds (there is no floor).
1 The cell is occupied by at least one object, occupied by an environment object (such as a wall), or otherwise not navigable (blocked by other objects).
0 The cell is unoccupied.

You can use an occupancy map for several purposes:

  • In scene generation, occupancy maps can be used to find free areas to place objects.
  • Occupancy maps can be used for pathfinding navigation.

The OccupancyMap add-on

To generate an occupancy map, you can use the OccupancyMap add-on, call generate(), and then call controller.communicate(commands):

from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.occupancy_map import OccupancyMap

c = Controller()
occupancy_map = OccupancyMap()
c.add_ons.append(occupancy_map)
occupancy_map.generate(cell_size=0.5)
c.communicate([TDWUtils.create_empty_room(6, 6),
               c.get_add_object(model_name="trunck",
                                object_id=c.get_unique_id(),
                                position={"x": 0, "y": 0, "z": 1.5})])
print(occupancy_map.occupancy_map)
c.communicate({"$type": "terminate"})

Output:

[[1 1 1 1 1 1 1 1 1 1 1]
 [1 0 0 0 0 0 0 0 0 0 1]
 [1 0 0 0 0 0 0 0 0 0 1]
 [1 0 0 0 0 0 0 0 0 0 1]
 [1 0 0 0 0 0 0 0 0 0 1]
 [1 0 0 0 0 0 0 0 0 0 1]
 [1 0 0 0 0 0 0 0 0 0 1]
 [1 0 0 0 1 1 1 0 0 0 1]
 [1 0 0 0 1 1 1 0 0 0 1]
 [1 0 0 0 1 1 1 0 0 0 1]
 [1 1 1 1 1 1 1 1 1 1 1]]

Occupancy map statuses

Value Meaning
0 The cell is unoccupied.
1 The cell is occupied by at least one object or occupied by an environment object (such as a wall).
2 The cell is out of bounds (there is no floor).
3 The cell is free, but it's in an isolated island.

Occupancy map positions

occupancy_map.positions is a 3D array where the first two axes correspond to occupancy_map.occupancy_map.

For example, occupancy_map.positions[0][1] might return [-2. -2.5] and its occupancy status is occupancy_map.occupancy_map[0][1], which in the above example returns 1 (occupied).

Cell Size

Set the cell_size parameter in generate() to adjust the size of each cell:

from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.occupancy_map import OccupancyMap

c = Controller()
occupancy_map = OccupancyMap()
c.add_ons.append(occupancy_map)
occupancy_map.generate(cell_size=1)
c.communicate([TDWUtils.create_empty_room(6, 6),
               c.get_add_object(model_name="trunck",
                                object_id=c.get_unique_id(),
                                position={"x": 0, "y": 0, "z": 1.5})])
print(occupancy_map.occupancy_map)
c.communicate({"$type": "terminate"})

Output (note that this map is smaller than the previous example, despite having the scene being exactly the same):

[[1 1 1 1 1 1]
 [1 0 0 0 0 1]
 [1 0 0 0 0 1]
 [1 0 0 0 0 1]
 [1 0 1 1 0 1]
 [1 1 1 1 1 1]]

Ignore objects

You might want the OccupancyMap to ignore certain objects. Examples:

  • You don't want the cell agent is in to be marked as "occupied"
  • You want to ignore small objects

Set the ignore_objects parameter of occupancy_map.generate() to ignore objects:

from tdw.controller import Controller
from tdw.tdw_utils import TDWUtils
from tdw.add_ons.occupancy_map import OccupancyMap

c = Controller()
occupancy_map = OccupancyMap()
c.add_ons.append(occupancy_map)
object_id = Controller.get_unique_id()
occupancy_map.generate(cell_size=1, ignore_objects=[object_id])
c.communicate([TDWUtils.create_empty_room(6, 6),
               c.get_add_object(model_name="trunck",
                                object_id=object_id,
                                position={"x": 0, "y": 0, "z": 1.5})])
print(occupancy_map.occupancy_map)
c.communicate({"$type": "terminate"})

Output:

[[1 1 1 1 1 1]
 [1 0 0 0 0 1]
 [1 0 0 0 0 1]
 [1 0 0 0 0 1]
 [1 0 0 0 0 1]
 [1 1 1 1 1 1]]

Regenerate every communicate() call

Occupancy maps are static. If an object in the scene moves, occupancy_map.occupancy_map won't update.

You can optionally regenerate the occupancy map on every communicate() call by setting generate(once=False). In general, it is relatively expensive to generate occupancy maps. If you need to continuously update your occupancy map, setting once=False is faster than calling generate() every communicate() call because the build will be able to use cached data.

Reset

You don't need to reset an OccupancyMap add-on. Simply call generate() followed by controller.communicate(commands) to create a new occupancy map.

This is the last document in the "Navigation" tutorial.

Return to the README

Example controllers:

Python API: