fix(Unreal): port signal height, trigger box, and trigger volume fixes by youtalk · Pull Request #9653 · carla-simulator/carla

youtalk · 2026-04-07T21:12:49Z

Description

Port of 3 ue4-dev bug fixes for traffic signal placement:

Traffic signals spawned in air (f856729ee) — Add AdjustSignHeightToGround method using line trace to place traffic signs/lights at ground level instead of floating in air.
Below ground trigger boxes (c1ba7342c) — Improve AdjustAllSignsToHeightGround with validity checks, bPositioned tracking, mesh-component-level Z adjustment.
Trigger volume for OpenDRIVE signals (2fed7136e) — Return only the first trigger volume (preserving rotation) instead of merging all volumes into one combined bounding box.

Where has this been tested?

Platform(s): Ubuntu 24.04
Python version(s): N/A (C++ only)
Unreal Engine version(s): 5.5

Possible Drawbacks

Traffic sign Z positions may change slightly on existing maps due to the new ground-snapping behavior.

This change is

Signed-off-by: Yutaka Kondo <yutaka.kondo@youtalk.jp>

update-docs · 2026-04-07T21:12:55Z

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would update our CHANGELOG.md based on your changes.

Copilot

Pull request overview

Ports Unreal-side fixes related to traffic signal/sign placement and trigger volume handling, aligning CARLA’s UE5 implementation with prior ue4-dev bug fixes for OpenDRIVE-generated signage.

Changes:

Snap traffic sign/light spawn Z to ground via line trace before spawning.
Add (currently unused) post-pass adjustment logic for already-spawned traffic signs, including per-mesh Z offsets and a positioned flag.
Change traffic sign bounding box selection to use a single trigger volume (first) to preserve rotation rather than merging volumes.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

File	Description
`Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Util/BoundingBoxCalculator.cpp`	Switch traffic-sign bounding box computation to return only the first trigger volume and preserve its rotation.
`Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Traffic/TrafficSignBase.h`	Add a `bPositioned` flag intended to prevent repeated repositioning.
`Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Traffic/TrafficLightManager.h`	Declare new helper methods for ground-snapping and post-adjustment.
`Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Traffic/TrafficLightManager.cpp`	Apply ground-snapping during spawning; add post-adjustment routine for already spawned signs.

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Copilot · 2026-04-07T21:31:36Z

Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Util/BoundingBoxCalculator.cpp

      auto TriggerVolumes = TrafficSign->GetTriggerVolumes();
      if (TriggerVolumes.Num() > 0)
      {
-        FBoundingBox Box = UBoundingBoxCalculator::CombineBoxes(TriggerVolumes);
+        UBoxComponent* FirstTriggerVolume = TriggerVolumes[0];
        FTransform Transform = Actor->GetActorTransform();
-        Box.Origin = Transform.InverseTransformPosition(Box.Origin);
-        Box.Rotation = Transform.InverseTransformRotation(Box.Rotation.Quaternion()).Rotator();
-        return Box;
+
+        FBoundingBox TVWorld;
+        TVWorld.Origin = FirstTriggerVolume->GetComponentLocation();
+        TVWorld.Extent = FirstTriggerVolume->GetScaledBoxExtent();
+        TVWorld.Rotation = FirstTriggerVolume->GetComponentRotation();


GetTriggerVolumes() can return an array containing nullptr (e.g., when the Blueprint GetTriggerVolume() isn't implemented or returns null). In that case TriggerVolumes.Num() > 0 is true but TriggerVolumes[0] will be null and this will crash when dereferenced. Consider skipping invalid entries and falling back to GetTriggerVolume() when the first valid trigger volume isn't found.

Copilot · 2026-04-07T21:31:36Z

Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Util/BoundingBoxCalculator.cpp

+        FBoundingBox TVWorld;
+        TVWorld.Origin = FirstTriggerVolume->GetComponentLocation();
+        TVWorld.Extent = FirstTriggerVolume->GetScaledBoxExtent();
+        TVWorld.Rotation = FirstTriggerVolume->GetComponentRotation();
+
+        FBoundingBox TVLocal;
+        TVLocal.Origin = Transform.InverseTransformPosition(TVWorld.Origin);
+        TVLocal.Extent = TVWorld.Extent;
+        TVLocal.Rotation = Transform.InverseTransformRotation(TVWorld.Rotation.Quaternion()).Rotator();
+


FBoundingBox documents Extent as being relative to its owner, but here TVLocal.Extent is copied from GetScaledBoxExtent() (world-scaled). If the actor (or any parent) has non-1 scale, the origin/rotation are converted to actor-local but the extent is not, producing an inconsistent local bounding box. Consider computing extent in actor-local space (e.g., based on relative transform / relative scale) rather than copying the world-scaled extent.

Copilot · 2026-04-07T21:31:37Z

Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Traffic/TrafficSignBase.h

  UFUNCTION(BlueprintImplementableEvent)
  UBoxComponent *GetTriggerVolume() const;

+  UPROPERTY(Category = "Traffic Sign", VisibleAnywhere, BlueprintReadOnly)


bPositioned is introduced as a public UPROPERTY(VisibleAnywhere, BlueprintReadOnly), but it’s only used as internal bookkeeping by ATrafficLightManager. Exposing it on the base actor makes it part of the reflected/Blueprint API surface and allows accidental changes from editor/Blueprints. Consider making it non-reflected (plain bool), moving the tracking into the manager, or at least making it private with controlled access.

Suggested change

UPROPERTY(Category = "Traffic Sign", VisibleAnywhere, BlueprintReadOnly)

Copilot · 2026-04-07T21:31:37Z

Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Traffic/TrafficLightManager.h

+  bool AdjustSignHeightToGround(FVector& SpawnLocation) const;
+
+  void AdjustAllSignsToHeightGround();
+


AdjustAllSignsToHeightGround() is declared/defined but not called anywhere in the codebase (search shows only declaration + definition). As a result, the new bPositioned flag and the mesh-level Z adjustment path appear to be dead code and the “below ground trigger boxes” fix described in the PR may not actually run. Either invoke this at an appropriate point (e.g., after spawning/generating traffic signs) or remove it to avoid carrying unused code.

Copilot · 2026-04-07T21:31:38Z

Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Traffic/TrafficLightManager.cpp

+      // Get all static mesh components
+      TArray<UStaticMeshComponent*> StaticMeshComps;
+      TS->GetComponents<UStaticMeshComponent>(StaticMeshComps);
+
+      for (UStaticMeshComponent* MeshComp : StaticMeshComps)
+      {
+        if (!MeshComp) continue;
+
+        // Skip if this has a mesh parent (it's a child)
+        USceneComponent* ParentComp = MeshComp->GetAttachParent();
+        if (ParentComp && Cast<UStaticMeshComponent>(ParentComp))
+        {
+          continue;
+        }
+
+        // Move the mesh component down
+        FVector CompLocation = MeshComp->GetRelativeLocation();
+        CompLocation.Z += ZOffset;
+        MeshComp->SetRelativeLocation(CompLocation);
+
+        MeshComp->UpdateBounds();
+
+        UE_LOG(LogCarla, Log, TEXT("Moved mesh %s by %f cm"), *TS->GetName(), ZOffset);
+      }


AdjustAllSignsToHeightGround() logs once per mesh component moved at Log level. When adjusting many traffic signs this can generate a large amount of log output (especially in editor tools / map generation). Consider lowering the verbosity (e.g., Verbose) and/or logging once per actor instead of once per component.

Copilot · 2026-04-07T21:31:38Z

Unreal/CarlaUnreal/Plugins/Carla/Source/Carla/Traffic/TrafficLightManager.cpp

+      float ZOffset = AdjustedLocation.Z - OriginalLocation.Z;
+
+      TS->GetRootComponent()->SetMobility(EComponentMobility::Movable);
+
+      // Get all static mesh components
+      TArray<UStaticMeshComponent*> StaticMeshComps;
+      TS->GetComponents<UStaticMeshComponent>(StaticMeshComps);
+
+      for (UStaticMeshComponent* MeshComp : StaticMeshComps)
+      {
+        if (!MeshComp) continue;
+
+        // Skip if this has a mesh parent (it's a child)
+        USceneComponent* ParentComp = MeshComp->GetAttachParent();
+        if (ParentComp && Cast<UStaticMeshComponent>(ParentComp))
+        {
+          continue;
+        }
+
+        // Move the mesh component down
+        FVector CompLocation = MeshComp->GetRelativeLocation();
+        CompLocation.Z += ZOffset;
+        MeshComp->SetRelativeLocation(CompLocation);
+
+        MeshComp->UpdateBounds();
+
+        UE_LOG(LogCarla, Log, TEXT("Moved mesh %s by %f cm"), *TS->GetName(), ZOffset);
+      }
+
+      TS->UpdateComponentTransforms();
+      TS->GetRootComponent()->SetMobility(EComponentMobility::Static);
+    }


AdjustAllSignsToHeightGround() unconditionally sets the root component mobility to Movable and then to Static. This can silently change signs that were authored with a different mobility setting. Consider capturing the original mobility and restoring it at the end (or only changing mobility when necessary).

fix(traffic): port signal height, trigger box, and trigger volume fixes

7649e0a

Signed-off-by: Yutaka Kondo <yutaka.kondo@youtalk.jp>

youtalk changed the title ~~fix(traffic): port signal height, trigger box, and trigger volume fixes~~ fix(Unreal): port signal height, trigger box, and trigger volume fixes Apr 7, 2026

youtalk marked this pull request as ready for review April 7, 2026 21:26

youtalk requested a review from a team as a code owner April 7, 2026 21:26

Copilot AI review requested due to automatic review settings April 7, 2026 21:26

Copilot started reviewing on behalf of youtalk April 7, 2026 21:27 View session

Copilot AI reviewed Apr 7, 2026

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youtalk mentioned this pull request Apr 7, 2026

Port ue4-dev features and fixes to ue5-dev (tracking issue) #9635

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JesusAnaya mentioned this pull request Apr 8, 2026

fix(Unreal): remove duplicate include in BoundingBoxCalculator #9656

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fix(Unreal): port signal height, trigger box, and trigger volume fixes#9653

fix(Unreal): port signal height, trigger box, and trigger volume fixes#9653
youtalk wants to merge 1 commit intocarla-simulator:ue5-devfrom
youtalk:fix/traffic-signal-placement

youtalk commented Apr 7, 2026 •

edited by Blyron

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		bool AdjustSignHeightToGround(FVector& SpawnLocation) const;

		void AdjustAllSignsToHeightGround();

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youtalk commented Apr 7, 2026 • edited by Blyron Loading Uh oh! There was an error while loading. Please reload this page.

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youtalk commented Apr 7, 2026 •

edited by Blyron

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