Navigation Meshes

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Revision as of 20:45, 2 July 2005 by Mungo (talk | contribs) (Using Mesh Editing Commands: added info and link to using a config file.)

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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

Enabling the Navigation Mesh editor in de_dust
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.

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.

Area Types

Jump areas (marked with green X's) tell bots that they must jump to reach the higher connected area, and that this area is not usable as a hiding/sniping spot.
Crouch areas (marked with a blue diagonal slash) force bots to crouch when moving through this area.

Connection Types

Bidirectional (two-way) connections (marked with light blue lines at the area edges) allow bots to freely move between the two areas.
One-way connections (marked with dark blue lines) are usually used for "jump-down" links from a high ledge to the ground. This tells the bots that they can jump down, but they can't jump back up. One-way links can also be useful for forcing bots to travel a specific direction, perhaps to set up for a tricky jump.

Using Mesh Editing Commands

Although all of the mesh editing commands can be typed in the console, in practice 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).

You can temporarily bind many commands at once by using a CFG file. This is useful for bot navigation editing, because there are many commands, and you will probably not want them to be permanently attached to your keys. See Bot Navigation Editing CFG File for a pre-made file and instructions on its use.

See Navigation Mesh Console Command Reference for a list of all commands related to bot navigation.

Basic Mesh Editing Commands

Save

Currently, there is no "undo" command in the Navigation Mesh editing system. Therefore, it is very important to save your work often via the nav_save command.

Split

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

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.

Marked first area Aim at second area 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 below.

Marked first area Aim at second area New area spliced between

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

Start dragging area at first corner Drag area extent Area created

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

Adding Place Names

Place Names can be assigned to areas to label that region of the map. For instance, if there is a prominent house in the map, all of the nav areas in the house can be tagged with the "House" Place Name.

Place Names are used by the CS Bot chatter system to announce where they are, as well as by the radar to show the current location of the player, and is appended to the player's name when they use text chat or radio commands.

To enter and leave "Place Painting Mode", execute nav_toggle_place_mode (assuming nav_edit is set to "1").

For a list of all available Place Names, execute nav_place_list.

Select a Place by typing nav_use_place (name). Then aim your cursor at an area you want to label with that Place Name and execute nav_toggle_place_painting. While "place painting" is active, each area you point at will be tagged with the current Place Name. To stop place painting, execute nav_toggle_place_painting again.

There are several additional commands that provide tools for picking, flood-filling, replacing, and so on. For a complete reference, see Place Name Commands.

Common Mesh Problems and Solutions

Extraneous Areas on Stairs and Ramps

The automatic generation system tends to build areas that hang off the side of stairs and ramps. These should be removed to force the bots to take the stairs or ramp straight-on.

Railings

Railings can be a problem for the current bot navigation system. Including jump-down links that must pass over railings should be avoided unless necessary. The bots will eventually make these jumps, but they are not terribly elegant while doing so.

Preventing Excessive Jumping

When to use the nav_no_jump flag.

Dealing with Rotating Doors

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

Advanced Editing Techniques

Ladders

Ladders can be manually built against climbable surfaces. Your editing cursor will turn green when pointing at a climbable surface.

Using nav_build_ladder

The easy way to build a ladder is to simply point at a climbable surface, and execute nav_build_ladder.

Point at a climbable surface Ladder created

Using nav_begin_area and nav_end_area

If nav_build_ladder isn't what you need, you can manually create a ladder:

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

This can be useful to get bots to start going up the ladder, and jump off halfway up, onto the crate:

Start dragging ladder at first corner Drag ladder extent Ladder created

Reversing ladders

Sometimes a ladder will be created facing the wrong way. If a ladder is drawn in red, you are looking at it from the back. The ladder is drawn in green if it is facing you. To change the orientation of a ladder, simply point at the ladder and use nav_ladder_flip.

Ladder facing into the wall (incorrect) Ladder facing away from the wall (correct)

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.

Lining up Tricky Jumps and Narrow Doorways

Arranging nav areas to force specific paths.


See also

Navigation Mesh Console Command Reference

Official forums for the bot system.