Tutorial 09 - Hybrid LCM Nav3D + Recast crowd avoidance

TL;DR: Add ULcmCrowdAvoidanceBridge to your LCM Nav3D flying pawn → stock UE5 UCrowdManager Detour RVO sees the LCM Nav3D pawn and steers Recast crowd agents around it. The Z-band filter (auto-applied by the bridge) prevents false-collision avoidance between agents at different vertical bands.

Prerequisites

• The third-person template (or any project with a Character + AIController).
• LCMNav3D plugin enabled.
• An ALcmNavigationManagerSVO in the level.
• An ALcmFlyingPawn (or your own LCM Nav3D flying pawn).

Step 1 - Add the bridge to your LCM Nav3D pawn

In the editor, select your LCM Nav3D pawn → Add Component → search "LCM Crowd Avoidance Bridge".

Defaults are sensible:

• bAutoRegister = true - registers with UCrowdManager on BeginPlay automatically
• AgentRadius = 50 cm - typical pawn radius
• AgentHalfHeight = 100 cm - cylinder extent for Detour
• MaxSpeed = 800 cm/s - matches ULcmNavMovementComponent default

That's it for the LCM Nav3D side.

Step 2 - Add Recast crowd agents (existing UE5 pattern)

Your Recast ground crowd agents should already use UCrowdFollowingComponent instead of the default UPathFollowingComponent. This is the standard UE5 setup for any project using crowd avoidance - LCM Nav3D doesn't change this. If you're not already on UCrowdFollowingComponent:

// In your AAIController subclass constructor
GetCharacterMovement()->bUseAccelerationForPaths = true;
//. and override the AIController to use UCrowdFollowingComponent

Or in Blueprint: the AIController's UCrowdFollowingComponent is auto-registered as the agent.

Step 3 - Play

Hit Play. Your LCM Nav3D flying pawn and Recast ground crowd agents now avoid each other (per the Z-band filter rules below).

How the Z-band filter works

Unreal's UCrowdManager Detour RVO assumes coplanar agents - out of the box, a flying LCM Nav3D agent at Z=500 would be flagged as a "neighbour" by a Recast ground agent at Z=0, producing avoidance behaviour that looks like the ground agent dodging an obstacle 5 meters overhead.

The bridge fixes this at the avoidance-group bitfield level:

• Each agent gets an AvoidanceGroup bit derived from its world Z divided by r.LcmNav.Crowd.ZBandHeightCm (default 200 cm).
• Each agent's GroupsToAvoid is set to its own band + the ±1 adjacent bands (so vertically close agents still see each other).
• Cross-band agents (e.g. ground Z=0 and aerial Z=500 with 200 cm bands → bands 0 and 2) ignore each other via Detour's standard bitfield mask.

Same engineering work, leverages stock Detour rather than fighting it.

Tuning r.LcmNav.Crowd.ZBandHeightCm

Set the CVar in PIE to live-tune, then commit to your project's DefaultEngine.ini once you're happy.

Stacked multi-floor scenarios

UCrowdManager is one global instance per world. For stacked-floor scenarios (e.g. LCM Nav3D agents at Z=200, 500, 800 sharing the same UCrowdManager), the Z-band filter handles it automatically - each pair of agents whose Z-distance is > 1 band-height ignores each other.

For truly independent crowds (each floor should be its own crowd zone), you'd need to spawn separate UCrowdManager instances per zone via project-side subclassing. This is out of scope for v1.

Performance notes

• Each registered LCM Nav3D bridge contributes ~1 RegisterAgent call at BeginPlay + ~7 virtual-call evaluations per Detour tick (Detour reads the ICrowdAgentInterface getters once per query).
• The Z-band filter eliminates ~99% of cross-band RVO computation cost - only agents within ±1 band of you contribute to your avoidance solve.
• Disabling the filter (r.LcmNav.Crowd.ZBandHeightCm = 0) restores legacy Detour coplanar behaviour for benchmarking.

Acceptance test (manual)

1. Spawn 5 Recast ground crowd agents in a circle at Z=0.
2. Spawn 1 LCM Nav3D flying pawn with ULcmCrowdAvoidanceBridge at Z=500.
3. Fly the LCM Nav3D pawn through the middle of the ground-agent circle.
4. Expected: ground agents continue their pathing without dodging the airborne pawn (Z-band separation > 200cm default).
5. Now fly the LCM Nav3D pawn down to Z=100 - ground agents dodge it.

If step 4 fails (ground agents dodge the airborne pawn), check r.LcmNav.Crowd.ZBandHeightCm is not 0.

What about the LCM Nav3D pawn's own avoidance?

Two paths, both work:

1. LCM Nav3D CBS/ORCA (default, the FlyTo task's built-in steering): the LCM Nav3D pawn avoids Recast crowd agents via the existing CBS context. Detour Crowd is purely the publishing surface to the rest of the world.

2. Use UCrowdFollowingComponent on the LCM Nav3D pawn: replace the LCM Nav3D pawn's AIController's UPathFollowingComponent with UCrowdFollowingComponent. The pawn becomes a full Detour Crowd participant - receives the suggested-velocity from Detour and applies it through its movement component. Combine with ULcmNavMovementComponent for the locomotion side.

Path 1 is the default; Path 2 is for projects that want a uniform crowd avoidance solver across LCM Nav3D and Recast agents.

Mass variant

The Mass-Entity equivalent (UApexCrowdMassBridgeProcessor) ships with T26 Mass Entity work - not yet available.

Related LCM Nav3D surfaces

• LCM_BTTask_FlyTo - already has CBS+ORCA built-in for LCM Nav3D-internal avoidance
• LCM_BTTask_EvadeCBS - pure-defensive evade using the same CBS context
• ULcmNavMovementComponent - LCM Nav3D-aware flying-pawn movement component