Navigation Meshes

Introduction

A Navigation Mesh represents the "walkable areas" of a map. This data is required by Bots and Hostages in Counter-Strike:Source, allowing them to "know" how to move around in the environment.

Navigation Mesh data is stored in a .nav file corresponding to the map file (.bsp) for which it is used. For example, the nav mesh for cstrike\maps\de_dust.bsp is stored in cstrike\maps\de_dust.nav.

Automatic Navigation Mesh Generation

To support the many community-created maps, Counter-Strike:Source includes an automatic mesh generation system. The first time you attempt to play a custom map with bots, the generation system will build a .nav file for that map. Depending on the size and complexity of the map, this may take a few minutes to a few hours. Most maps take about 5 minutes to auto-generate a .nav file. Once the generation is complete, a .nav file is saved to your hard drive for future use.

What is Computed During Generation

The following steps occur during Navigation Mesh generation:

• Starting at a player spawn point, walkable space is sampled by "flood-filling" outwards from that spot, searching for adjacent walkable points
• Rectangular Navigation Areas are constructed from the sampled data
• Hiding and Sniper spots are computed
• Encounter Spots and Approach Points are computed (this can take awhile)
• Initial Encounter areas are computed

Manually Starting the Generation Process

To start the generation process manually, type nav_generate from the console.

Viewing the Navigation Mesh

To see the resulting Navigation Mesh, type nav_edit 1. To turn the mesh editor off, type nav_edit 0.

Explicity Marking Walkable Areas (ie: "There's no mesh upstairs")

Some maps that have very steep stairs, ramps, or hills may confuse the generation system, resulting in the Navigation Mesh not covering the entire map. To solve this, you can manually place additional walkable markers that tell the generator to search outwards from that point during its sampling phase.

To add one or more walkable markers, first aim your view towards a known walkable spot in your map, then type nav_mark_walkable in the console. When you are finished placing markers, type nav_generate to re-generate the mesh.

Quickly Generating Meshes for Testing

The analysis phase of the generator can be quite time consuming. To skip it, type nav_quicksave 1 in the console.

NOTE: "Quicksaving" skips the analysis phase, and the resultant nav mesh will be missing important data required by the CS Bots and Hostages higher-level planning and attention systems. While useful for testing, editing, and tuning a nav mesh, be sure to do a full analyze (ie: with nav_quicksave 0) before publishing your nav file to others.

Editing the Navigation Mesh

The automated Navigation Mesh generator does a reasonable job of constructing a mesh, allowing you to start using Bots and Hostages on custom maps easily.

However, careful hand-tuning of the Navigation Mesh can markedly improve the performance of Bots. In addition, manually decorating the mesh with Place Names allows the Bots to tell others where events occur, enhances the Counter-Strike radar and includes Place Names in all radio messages.

Enabling the Navigation Mesh editor in de_dust

The Navigation Mesh Editor

To enable the editor, type nav_edit 1 in the console (type nav_edit 0 to disable it).

• The white cross in the center of your view is the cursor.
• The Navigation Area you are pointing at is the selected area and is shown with a yellow outline.
• Navigation Areas that can be reached from the selected area are shown in red.
• The white line in the selected area denotes where the area will be split if the nav_split command is executed.

Using Mesh Editing Commands

Although all of the mesh editing commands can be typed in the console, in practise it is far easier to bind these commands to keys. For example, bind del nav_delete binds the delete key to the command nav_delete. After this binding, pressing the delete key will delete the nav area under your cursor (if you are nav editing mode).

Basic Mesh Editing Commands

Split

To split an area into two adjacent, inter-connected areas, aim your cursor at an area and execute the nav_split command.

Merge

To merge two adjacent areas:

1. Aim your cursor at the first area and execute nav_mark
2. Aim your cursor at the second area and execute nav_merge

Note that both areas must be the same size along the edge to be merged.

The resulting area will retain all of the connections of the original two areas, and inherit properties (ie: Place Names, etc) from the marked area.

Splice

Splicing creates a new area between two existing areas. Splicing is a powerful tool, and can be used to easily create sloped areas, as shown in the example.

Delete

To delete an area, aim your cursor at it and execute nav_delete

Creating a New Area

To manually create a new area:

1. Place your cursor at where a corner of the new area should be
2. Execute nav_begin_area
3. Move your cursor to drag out the area's extent
4. Execute nav_end_area

Adding and Removing Connections Between Areas

The connections between areas define whether an agent can move from one area to another. Usually these connections are bidirectional, meaning agents can move back and forth between two areas at will. However, sometimes the connection is one way, as in the case of high ledges that can be jumped down, but not back up.

To make a one-way connection from area A to area B (meaning you can move from A to B):

1. Place your cursor on area A
2. Mark area A with nav_mark
3. Aim your cursor at area B
4. Execute nav_connect

To make a bidirectional connection, repeat the above steps reversing the roles of A and B.

To remove all connections from areas A and B:

1. Aim at area A
2. Mark area A with nav_mark
3. Aim at area B
4. Execute nav_disconnect

Advanced Editing Techniques

Ladders

Editing ladders in the nav mesh.

Preventing Excessive Jumping

When to use the nav_no_jump flag.

Obstacle Avoidance and Precision Movement

Using nav_precise, nav_walk, and nav_stop to disable local obstacle avoidance behaviors and control bot movement.

Marking Areas to Avoid

Using nav_avoid to tell bots to avoid the area unless the normal route has become too dangerous.

Controlling Where Bots Can Hide

Using nav_no_hide to prevent bots from hiding in that area. How to force the creation of hiding spots during the analysis phase.

Dealing with Rotating Doors

Carving out empty space in the nav mesh to allow for the rotating door.

Lining up Tricky Jumps and Narrow Doorways

Arranging nav areas to force specific paths.

Navigation Mesh Console Command Reference

Commands

Mesh Generation

nav_generate

Generate a Navigation Mesh for the current map and save it to disk.

nav_generate_incremental

Run the generation process again without altering the existing mesh. If there are additional walkable areas and/or walkable_marks, new areas will be generated and added to the mesh. Note that these new areas will have to be manually connected to the existing mesh.

nav_analyze

Analyze the current Navigation Mesh and save it to disk. The analysis phase computes the second-order data needed by the bots for their planning and attention systems.

nav_mark_walkable

Mark the current location as a walkable position. These positions are used as seed locations when sampling the map to generate a Navigation Mesh.

nav_clear_walkable_marks

Erase any previously placed walkable positions.

nav_save

Saves the current Navigation Mesh to disk.

nav_load

Loads the Navigation Mesh for the current map.

Editing Commands

nav_delete

Deletes the currently highlighted Area.

nav_split

To split an Area into two, align the split line using your cursor and invoke the split command.

nav_make_sniper_spots

Chops the marked area into disconnected sub-areas suitable for sniper spots.

nav_merge

To merge two Areas into one, mark the first Area, highlight the second by pointing your cursor at it, and invoke the merge command.

nav_mark

Marks the Area or Ladder under the cursor for manipulation by subsequent editing commands.

nav_unmark

Clears the marked Area or Ladder.

nav_begin_area

Defines a corner of a new Area or Ladder. To complete the Area or Ladder, drag the opposite corner to the desired location and issue a 'nav_end_area' command.

nav_end_area

Defines the second corner of a new Area or Ladder and creates it.

nav_connect

To connect two Areas, mark the first Area, highlight the second Area, then invoke the connect command. Note that this creates a one-way connection from the first to the second Area. To make a two-way connection, also connect the second area to the first.

nav_disconnect

To disconnect two Areas, mark an Area, highlight a second Area, then invoke the disconnect command. This will remove all connections between the two Areas.

nav_splice

To splice, mark an area, highlight a second area, then invoke the splice command to create a new, connected area between them.

nav_corner_select

Select a corner of the currently marked Area. Use multiple times to access all four corners.

nav_corner_raise

Raise the selected corner of the currently marked Area.

nav_corner_lower

Lower the selected corner of the currently marked Area.

nav_corner_place_on_ground

Places the selected corner of the currently marked Area on the ground.

Bot Navigation Modification Commands

nav_crouch

Toggles the 'must crouch in this area' flag used by the AI system.

nav_precise

Toggles the 'dont avoid obstacles' flag used by the AI system.

nav_jump

Toggles the 'traverse this area by jumping' flag used by the AI system.

nav_no_jump

Toggles the 'dont jump in this area' flag used by the AI system.

nav_stop

Toggles the 'must stop when entering this area' flag used by the AI system.

nav_walk

Toggles the 'traverse this area by walking' flag used by the AI system.

nav_run

Toggles the 'traverse this area by running' flag used by the AI system.

nav_avoid

Toggles the 'avoid this area when possible' flag used by the AI system.

nav_transient

Toggles the 'area is transient and may become blocked' flag used by the AI system.

nav_dont_hide

Toggles the 'area is not suitable for hiding spots' flag used by the AI system.

nav_stand

Toggles the 'stand while hiding' flag used by the AI system.

nav_no_hostages

Toggles the 'hostages cannot use this area' flag used by the AI system.

Place Name Commands

nav_use_place

If used without arguments, all available Places will be listed. If a Place argument is given, the current Place is set.

nav_place_replace

Replaces all instances of the first place with the second place.

nav_place_list

Lists all place names used in the map.

nav_toggle_place_mode

Toggle the editor into and out of Place mode. Place mode allows labelling of Area with Place names.

nav_set_place_mode

Sets the editor into or out of Place mode. Place mode allows labelling of Area with Place names.

nav_place_floodfill

Sets the Place of the Area under the cursor to the curent Place, and 'flood-fills' the Place to all adjacent Areas. Flood-filling stops when it hits an Area with the same Place, or a different Place than that of the initial Area.

nav_place_pick

Sets the current Place to the Place of the Area under the cursor.

nav_toggle_place_painting

Toggles Place Painting mode. When Place Painting, pointing at an Area will 'paint' it with the current Place.

Other Commands

nav_check_file_consistency

Scans the maps directory and reports any missing/out-of-date navigation files.

nav_update_blocked

Updates the blocked/unblocked status for every nav area.

nav_check_floor

Updates the blocked/unblocked status for every nav area.

nav_remove_unused_jump_areas

Removes jump areas with at most 1 connection to a ladder or non-jump area.

nav_strip

Strips all Hiding Spots, Approach Points, and Encounter Spots from all Areas in the mesh.

nav_mark_unnamed

Mark an Area with no Place name. Useful for finding stray areas missed when Place Painting.

nav_warp_to_mark

Warps the player to the marked area.

nav_ladder_flip

Flips the selected ladder's direction.

nav_compress_id

Re-orders area and ladder ID's so they are continuous.

nav_show_ladder_bounds

Draws the bounding boxes of all func_ladders in the map.

nav_build_ladder

Attempts to build a nav ladder on the climbable surface under the cursor.

Console Variables

nav_coplanar_slope_limit value

nav_split_place_on_ground (0 or 1)

If set to 1, nav areas will be placed flush with the ground when split.

nav_area_bgcolor R G B A

RGBA color to draw as the background color for nav areas while editing.

nav_show_area_info duration

Duration in seconds to show nav area ID and attributes while editing

nav_snap_to_grid (0 or 1)

If set to 1, snap to the nav generation grid when creating new nav areas

nav_create_place_on_ground (0 or 1)

If set to 1, nav areas will be placed flush with the ground when created by hand.

nav_draw_limit count

The maximum number of areas to draw in edit mode

nav_slope_limit Z

The ground unit normal's Z component must be greater than this for nav areas to be generated.

nav_restart_after_analysis (0 or 1)

If set to 1, when nav nav_restart_after_analysis finishes, restart the server. Turning this off can cause crashes, but is useful for incremental generation.

nav_edit (0 or 1)

Set to one to interactively edit the Navigation Mesh. Set to zero to leave edit mode.

nav_quicksave (0 or 1)

Set to one to skip the time consuming phases of the analysis. Useful for data collection and testing.

nav_show_approach_points (0 or 1)

Show Approach Points in the Navigation Mesh.

nav_show_danger (0 or 1)

Show current 'danger' levels.

nav_show_player_counts (0 or 1)

Show current player counts in each area.

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Addition information can be found here.