NAV (file format)

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A NAV file is a Navigation Mesh file for Counter-Strike: Source bots, Left 4 Dead bots, Left 4 Dead 2 bots and Team Fortress 2 bots and NPCs. It defines, among other things the walkable space in a level. The file is not generated automatically when bots are played for the first time on a specific map, meaning that the bots will stand around helplessly. One can edit a Navigation Mesh manually by typing nav_edit 1 in the console with sv_cheats enabled. NAV creation is an open-source task available in the SDK. If one were to implement their bots, it would be easier because NAV creation is already supplied.

The difference between an AIN and a NAV file is that an AIN file is mainly used for NPC navigation.

File format

Note: This is reverse engineered data. Reverse engineered format code can also be found here.

unsigned int magicNumber; // Magic number to check if the file is a .nav file
unsigned int version; // Version of the .nav file, for example GMod and TF2 has 16

if ( version >= 10 ) {
	unsigned int subVersion; // Sub version of the .nav file, for example GMod has 0, TF2 has 2. This is usedt
}

if ( version >= 4 ) {
	unsigned int saveBspSize; // Size of source bsp file to verify that the bsp hasn't changed
}

if ( version >= 14 ) {
	unsigned char isAnalyzed;
}

if ( version >= 5 ) {
	// Places data. This is the "Mid", "Banana", etc stuff that is used in this nav mesh
	unsigned short count;

	for( int i = 0; i < count; ++i ) {
		unsigned short len; // length of the name
		char name[len]; // The name. Maximum len is 256
	}

	if ( version > 11 ) {
		unsigned char m_hasUnnamedAreas;
	}
}

{
	// Load custom data pre area
	// This is by default is completely unused, it is left for mods to store custom data
}

unsigned int count; // number of CNavAreas

{
	// PreLoadAreas( count )
	// This is by default is completely unused, it is left for mods to store custom data
	// Assuming that the data is per nav area
	//for( int i = 0; i < count; ++i ) {
	//}
}

for( i = 0; i < count; ++i ) {
	// Per CNavArea data
	unsigned int id; // ID of the CNavArea

	// Attribute flags
	if ( version <= 8 ) {
		unsigned char attributeFlags;
	} else if ( version < 13 ) {
		unsigned short attributeFlags;
	} else {
		int attributeFlags;
	}

	Vector m_nwCorner; // size is 3 * float(x,y,z), North-West corner of the area
	Vector m_seCorner; // size is 3 * float(x,y,z), South-East corner of the area
	
	// More data...
}

if ( version >= 6 ) {
	unsigned int count; // number of CNavAreas

	for( i = 0; i < count; ++i ) {
		// Ladder data
	}
}

{
	// Load Custom Data
	// Again, by default this is unused
}

See also

• Navigation Meshes
• Nav file parser in Go