View source for Nav Mesh

A ''Navigation Mesh'' represents the "walkable areas" of a map. This data is '''required''' by [[bot|Bots]] and Hostages in [[Counter-Strike: Source]], as well for Bots and Infected in [[Left 4 Dead]], 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 <code>cstrike\maps\de_dust.bsp</code> is stored in <code>cstrike\maps\de_dust.nav</code>.

= 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 <code>nav_generate</code> from the console.

== Viewing the navigation mesh ==
To see the resulting Navigation Mesh, type <code>nav_edit 1</code>.  To turn the mesh editor off, type <code>nav_edit 0</code>. You will need to have <code>sv_cheats 1</code> to be able to view the navigation mesh.

== Explicitly marking walkable areas (i.e: "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 <code>nav_mark_walkable</code> in the console.  When you are finished placing markers, type <code>nav_generate</code> 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 <code>nav_quicksave 1</code> 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: <code>nav_analyze</code> with <code>nav_quicksave 0</code>) before publishing your nav file to others.}}

= Editing the navigation mesh =
[[Image:nav_edit.jpg|thumb|300px|right|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 <code>nav_edit 1</code> in the console (type <code>nav_edit 0</code> 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 <code>nav_split</code> command is executed.

=== Area types ===
[[Image:nav_jump.jpg|300px|thumb|left|'''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.]]
[[Image:nav_crouch.jpg|300px|thumb|left|'''Crouch areas''' (marked with a blue diagonal slash) force bots to crouch when moving through this area.]]{{clr}}

=== Connection types ===
[[Image:nav_connections.jpg|300px|thumb|left|'''Bidirectional (two-way) connections''' (marked with light blue lines at the area edges) allow bots to freely move between the two areas.]]
[[Image:nav_jump_down.jpg|300px|thumb|left|'''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.]]{{clr}}

== 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, <code>bind del nav_delete</code> 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 [[Editing Bot Navigation CFG File]] for a pre-made file and instructions on its use.

See [[Counter-Strike: Source Navigation Mesh Console Command Reference|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 <code>nav_save</code> command.

=== Split ===
To split an area into two adjacent, inter-connected areas, aim your cursor at an area and execute the <code>nav_split</code> command.

[[Image:nav_edit.jpg|300px|thumb|left|Before split]]
[[Image:nav_split.jpg|300px|thumb|left|After split]]{{clr}}

=== Merge ===
To merge two adjacent areas:
# Aim your cursor at the first area and execute <code>nav_mark</code>
# Aim your cursor at the second area and execute <code>nav_merge</code>

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

[[Image:nav_mark.jpg|300px|thumb|left|Marked first area]]
[[Image:nav_pre_merge.jpg|300px|thumb|left|Aim at second area]]
[[Image:nav_post_merge.jpg|300px|thumb|left|Merged]]{{clr}}

The resulting area will retain all of the connections of the original two areas, and inherit properties (i.e: 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.

To splice a new area in between two existing areas:
# Aim your cursor at the first area and execute <code>nav_mark</code>
# Aim your cursor at the second area and execute <code>nav_splice</code>

[[Image:nav_prep_splice.jpg|300px|thumb|left|Marked first area]]
[[Image:nav_pre_splice.jpg|300px|thumb|left|Aim at second area]]
[[Image:nav_post_splice.jpg|300px|thumb|left|New area spliced between]]{{clr}}

=== Delete ===
To delete an area, aim your cursor at it and execute <code>nav_delete</code>

=== Creating a new area ===
To manually create a new area:
# Place your cursor at where a corner of the new area should be
# Execute <code>nav_begin_area</code>
# Move your cursor to drag out the area's extent
# Execute <code>nav_end_area</code>

[[Image:nav_begin_area.jpg|300px|thumb|left|Start dragging area at first corner]]
[[Image:nav_drag_area.jpg|300px|thumb|left|Drag area extent]]
[[Image:nav_end_area.jpg|300px|thumb|left|Area created]]{{clr}}

=== 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):
# Place your cursor on area A
# Mark area A with <code>nav_mark</code>
# Aim your cursor at area B
# Execute <code>nav_connect</code>

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:
# Aim at area A
# Mark area A with <code>nav_mark</code>
# Aim at area B
# Execute <code>nav_disconnect</code>

== 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 <code>nav_toggle_place_mode</code> (assuming <code>nav_edit</code> is set to "1").

For a list of all available Place Names, execute <code>nav_place_list</code>.  Or, you can look in this wiki at the [[Standard Place Names for CSS]], if you are working on a CSS map.

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

There are several additional commands that provide tools for picking, flood-filling, replacing, and so on.  For a complete reference, see [[Navigation_Mesh_Commands#Place_name_commands|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 ===
Mark an area with <code>nav_mark</code>and use the <code>nav_no_jump</code> command to flag the area to discourage jumping.

=== 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 <code>nav_build_ladder</code>'''

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

[[Image:nav_build_ladder_before.jpg|300px|thumb|left|Point at a climbable surface]]
[[Image:nav_build_ladder_after.jpg|300px|thumb|left|Ladder created]]{{clr}}

'''Using <code>nav_begin_area</code> and <code>nav_end_area</code>'''

If <code>nav_build_ladder</code> isn't what you need, you can manually create a ladder:
#Place your cursor at where a corner of the new ladder should be
# Execute <code>nav_begin_area</code>
# Move your cursor to drag out the ladder's extent
# Execute <code>nav_end_area</code>

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

[[Image:nav_begin_ladder.jpg|300px|thumb|left|Start dragging ladder at first corner]]
[[Image:nav_drag_ladder.jpg|300px|thumb|left|Drag ladder extent]]
[[Image:nav_end_ladder.jpg|300px|thumb|left|Ladder created]]{{clr}}

=== 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 <code>nav_ladder_flip</code>.

[[Image:nav_ladder_backward.jpg|300px|thumb|left|Ladder facing into the wall (incorrect)]]
[[Image:nav_ladder_forward.jpg|300px|thumb|left|Ladder facing away from the wall (correct)]]{{clr}}

=== Obstacle avoidance and precision movement ===
Using <code>nav_precise</code>, <code>nav_walk</code>, and <code>nav_stop</code> to disable local obstacle avoidance behaviors and control bot movement.

=== Marking areas to avoid ===
Using <code>nav_avoid</code> to tell bots to avoid the area unless the normal route has become too dangerous.

=== Controlling where bots Can hide ===
Using <code>nav_no_hide</code> to prevent bots from hiding in that area.
This can be used to force the creation of hiding spots during the analysis phase.

=== Setting up sniper spots ===
Mark an area using <code>nav_walk</code> and execute <code>nav_make_sniper_spots</code>. This will break the area into small sub-areas which are used internally by the navigation mesh to encourage sniping.

=== Lining up tricky jumps and narrow doorways ===
Arranging nav areas to force specific paths.

* If the bots are getting hung up on the sides of a door or window, you can carve out a narrow path through the middle of the opening.
* The highest a bot will try to jump is 58 units.  If the top of a jump is 59 or more units above the bottom, bots will give up as soon as they jump.  If this happens in a spot that the bots can actually jump up to, use <code>nav_corner_lower</code> to lower the upper nav area slightly.

[[Image:MaximumJumpCrouch.jpg|300px|thumb|left|Highest possible crouchjump]]{{clr}}

= See also =
* [[Navigation Mesh Commands|Navigation Mesh Console Command Reference]]

= External Links =
* Official forums for the bot system (down) - [http://web.archive.org/web/*/http://www.turtlerockstudios.com/forums/csbot/ Archived version].
* [http://www.editlife.net/tutorial.php?tutid=60 Waypointing for CS:S Bots/Hostages (Edit Life)]

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{{otherlang:en:jp|Bot Navigation for Counter-Strike:Source:jp}}

[[Category:Level Design]]