Different NavigationRegions can connect their navigation meshes without the need for a NavigationLink
as long as they are within navigation map edge_connection_margin and have compatible navigation_layers.
As soon as the distance becomes too large, building valid connections becomes a problem - a problem that NavigationLinks can solve.
NavigationLinks share many properties with NavigationRegions like navigation_layers.
NavigationLinks add a single connection between two positions over an arbitrary distance
compared to NavigationRegions that add a more local traversable area with a navigation mesh resource.
NavigationLinks have a start_position and end_position and can go in both directions when bidirectional is enabled.
When placed a navigationlink connects the navigation mesh polygons closest to its start_position and end_position within search radius for pathfinding.
The polygon search radius can be configured globally in the ProjectSettings under navigation/2d_or_3d/default_link_connection_radius
or set for each navigation map individually using the NavigationServer.map_set_link_connection_radius() function.
Both start_position and end_position have debug markers in the Editor.
The visible radius of a position shows the polygon search radius.
All navigation mesh polygons inside are compared and the closest is picked for the edge connection.
If no valid polygon is found within the search radius the navigation link gets disabled.
The link debug visuals can be changed in the Editor ProjectSettings under debug/shapes/navigation.
The visibility of the debug can also be controlled in the Editor 3D Viewport gizmo menu.
NavigationLinks do not move agents between the two link positions by themselves.
A navigation link does not provide any automated movement through the link. Instead, when
an agent reaches the position of a link, game code needs to react (e.g. through area triggers) and provide means for the agent
to move through the link to end up at the links other position (e.g. through teleport or animation) to continue along the path.