Tutorial 05: Dynamic Obstacles

TL;DR: Add an LCM Nav3D Dynamic Obstacle component to any actor that moves. It restamps the octree as the actor moves and agents reroute around it: closing doors, rising platforms, patrolling hazards, destructible cover.

Time: ~15 minutes. Assumes Tutorial 03.

Static vs dynamic

When the navigation volume is built, all static geometry is baked in. That bake is what makes queries fast, but it's a snapshot.

• Never moves? Do nothing. It's already in the octree.
• Moves? It needs a Dynamic Obstacle component, or the octree will keep believing the space is empty and agents will fly straight through it.

The common mistake: moving a static-mesh actor at runtime without the component. Nothing errors: agents ignore it, because as far as the navigation data is concerned it never moved.

Step 1: Make a moving obstacle

1. Create a Blueprint Actor, BP_MovingWall.
2. Add a Static Mesh component: a Cube, scaled to something that genuinely blocks a route (say 400 × 100 × 400).
3. Make sure the mesh has collision enabled. The voxelizer finds obstacles via collision, so a mesh set to No Collision is invisible to navigation.

Step 2: Add the Dynamic Obstacle component

1. In BP_MovingWall, Add Component → search "LCM Nav3D Dynamic Obstacle".
2. That's the whole setup. It auto-registers with the navigation manager at BeginPlay and tracks its owner from then on.

The settings

Tracked Components is worth knowing about. On an actor where only one part obstructs (a gate inside a decorative frame, a swinging arm on a fixed base), pick just that component. Only its movement restamps the octree, and only its bounds block agents.

You can also manage this at runtime from Blueprint with Add Tracked Component and Remove Tracked Component.

Step 3: Move it

Give it motion. The simplest version, in the Event Graph:

Event Tick ─→ SetActorLocation( StartLocation + (0, sin(GameTime) * 700, 0) )

Or use a Timeline, a matinee/sequencer track, physics; it doesn't matter. The component watches the transform, however it changes.

Step 4: See it work

1. Place BP_MovingWall so it periodically seals the only route between your flyer and its goal.
2. Press Play.

The agent should path around the wall, and when the wall closes the route, re-plan and take a different way.

To watch it happen: tick Draw Debug Volumes on the navigation manager. You'll see the voxels under the wall flip to blocked as it moves. That's the restamp.

How agents notice

Agents re-plan automatically. The relevant setting is on the navigation manager:

Lower = more reactive, more CPU. 0.1 is a good balance. For fast-moving hazards where agents must react instantly, try 0.05.

Ready-made examples

These demo maps show this working. Open any of them and read the setup:

The obstacles in these maps are driven along splines by the bundled BP_SplineMove Blueprint (Content/Blueprints/), so you can see a complete working rig rather than assembling one. For a simpler ping-pong mover the plugin also ships the LCM Nav3D Obstacle Mover component, below.

The bundled Obstacle Mover

The plugin ships a small helper so the demo maps move without Blueprint wiring, and it's useful in your own prototypes.

LCM Nav3D Obstacle Mover ping-pongs its owner between its start pose and an offset.

Pair it with a Dynamic Obstacle component on the same actor and you have a moving obstacle with zero scripting. It moves the actor kinematically, which is exactly what the obstacle tracker expects.

There's a companion LCM Nav3D Agent Driver used by the demo maps to loop a pawn between two tagged points (LcmGoalA / LcmGoalB) using the real async navigation stack, handy for testing a level without authoring a full BT.

Performance notes

Dynamic obstacles are not free: each restamp re-voxelizes a region.

Keep it cheap:

• Prefer fewer, larger dynamic obstacles over many small ones.
• Raise Update Distance Threshold for things that move constantly but don't need precision.
• Use Tracked Components so only the genuinely blocking part is considered.
• If something moves but can never block a route (debris, VFX props, decoration), don't give it the component at all.

Don't put a Dynamic Obstacle component on your navigating agents. Agents avoid each other through the avoidance system (Tutorial 03 Step 7); making them obstacles too means each one is constantly re-voxelizing the world around itself.

Troubleshooting

More: Troubleshooting.

Where to go next

You now have the whole core loop: a navigation volume, agents that fly through it, and a world that can change underneath them. From here, pick what your project needs: