Heuristic:CARLA simulator Carla Walker Spawn Vertical Offset
| Knowledge Sources | |
|---|---|
| Domains | Simulation, Debugging |
| Last Updated | 2026-02-15 07:00 GMT |
Overview
Apply a +2 unit vertical offset to walker spawn locations from the navigation mesh to prevent collision-induced spawn failures.
Description
When spawning pedestrians (walkers) in CARLA, the navigation mesh returns ground-level locations via `world.get_random_location_from_navigation()`. Spawning walkers exactly at ground level frequently causes collision detection failures because the walker's collision volume intersects with the ground plane. The official generate_traffic.py example applies a Z-offset of +2 to all walker spawn points to avoid this issue. The walkers then settle to the ground via gravity in the next simulation tick.
Usage
Use this heuristic whenever spawning walkers programmatically using `get_random_location_from_navigation()`. This is especially important when batch-spawning many walkers, where even a small failure rate compounds into significant losses.
The Insight (Rule of Thumb)
- Action: Add `spawn_point.location.z += 2` after getting a location from the navigation mesh.
- Value: Z offset of `2` (CARLA units, approximately 2 cm in real scale depending on map).
- Trade-off: Walkers briefly appear floating for one tick before settling to ground. No visual impact in practice since it resolves within one simulation step.
Reasoning
The navigation mesh provides 2D surface positions that may be slightly below or exactly at the collision surface. CARLA's spawn collision detection rejects actors whose bounding boxes overlap with existing geometry. A small upward offset ensures the walker spawns above the surface and settles via physics. The code comment in generate_traffic.py:222 explicitly states: "Apply Offset in vertical to avoid collision spawning".
# PythonAPI/examples/generate_traffic.py:216-223
for i in range(args.number_of_walkers):
spawn_point = carla.Transform()
loc = world.get_random_location_from_navigation()
if (loc != None):
spawn_point.location = loc
#Apply Offset in vertical to avoid collision spawning
spawn_point.location.z += 2
spawn_points.append(spawn_point)