NAV Format Reference (REWiki)

.NAV

The NAV files include a list of navigation points and their properties. The first number gives the number of navigation points. 7 types are available (in the following order):

0 - TGT - Target (can also be a group of targets)
1 - TUN - Tunnel entrance
2 - CHK - Checkpoint
3 - DUN - Departure Unit (level end)
4 - XIT - Tunnel exit
5 - BOS - Boss 
6 -       Starting point

Different types have different properties but all of them have at least identifier, position and description (unused).

Pitch, roll and yaw are the starting angles for the player's ship.

The departure unit is automatically created when the last navigation point is of type 3. If the last point is a tunnel exit, the level ends immediately after exiting the tunnel. This applies for every other type. When no nav-point is set, the level ends as soon as it starts. The NAV system is poorly integrated. It's possible to simply skip some of the navigation points and, in some cases, the entire list (2 examples):

1) Whenever there's a point of type 1 in the list (tunnel entrance), everything before this point can be skipped. The only exception are targets with more than one sub-target.

2) If the boss fight takes place in a chamber and you know the position of this chamber on the map, you can simply fly into the boss's tunnel to complete the level without even seeing the boss! But this works only if the last tunnel is part of the navigation list.