Making the result of radar deterministic

Unreal/CarlaUE4/Plugins/Carla/Source/Carla/Sensor/Radar.cpp

@@ -105,12 +105,21 @@ void ARadar::SendLineTraces(float DeltaTime)
   const float MaxRy = FMath::Tan(FMath::DegreesToRadians(VerticalFOV * 0.5f)) * Range;
   const int NumPoints = (int)(PointsPerSecond * DeltaTime);
 
+  // Generate the parameters of the rays in a deterministic way
+  Rays.clear();
+  Rays.resize(NumPoints);
+  for (int i = 0; i < Rays.size(); i++) {
+    Rays[i].Radius = RandomEngine->GetUniformFloat();
+    Rays[i].Angle = RandomEngine->GetUniformFloatInRange(0.0f, carla::geom::Math::Pi2<float>());
+    Rays[i].Hitted = false;
+  }
+
   FCriticalSection Mutex;
   GetWorld()->GetPhysicsScene()->GetPxScene()->lockRead();
-  ParallelFor(NumPoints, [&](int32 idxChannel) {
+  ParallelFor(NumPoints, [&](int32 idx) {
     FHitResult OutHit(ForceInit);
-    const float Radius = RandomEngine->GetUniformFloat();
-    const float Angle = RandomEngine->GetUniformFloatInRange(0.0f, carla::geom::Math::Pi2<float>());
+    const float Radius = Rays[idx].Radius;
+    const float Angle  = Rays[idx].Angle;
 
     float Sin, Cos;
     FMath::SinCos(&Sin, &Cos, Angle);
@@ -132,27 +141,34 @@ void ARadar::SendLineTraces(float DeltaTime)
 
     const TWeakObjectPtr<AActor> HittedActor = OutHit.Actor;
     if (Hitted && HittedActor.Get()) {
+      Rays[idx].Hitted = true;
 
-      const float RelativeVelocity = CalculateRelativeVelocity(OutHit, RadarLocation);
+      Rays[idx].RelativeVelocity = CalculateRelativeVelocity(OutHit, RadarLocation);
 
-      const FVector2D AzimuthAndElevation = FMath::GetAzimuthAndElevation (
+      Rays[idx].AzimuthAndElevation = FMath::GetAzimuthAndElevation (
         (EndLocation - RadarLocation).GetSafeNormal() * Range,
         TransformXAxis,
         TransformYAxis,
         TransformZAxis
       );
 
-      Mutex.Lock();
-      RadarData.WriteDetection({
-        RelativeVelocity,
-        AzimuthAndElevation.X,
-        AzimuthAndElevation.Y,
-        OutHit.Distance * TO_METERS
-      });
-      Mutex.Unlock();
+      Rays[idx].Distance = OutHit.Distance * TO_METERS;
     }
   });
   GetWorld()->GetPhysicsScene()->GetPxScene()->unlockRead();
+
+  // Write the detections in the output structure
+  for (auto& ray : Rays) {
+    if (ray.Hitted) {
+      RadarData.WriteDetection({
+        ray.RelativeVelocity,
+        ray.AzimuthAndElevation.X,
+        ray.AzimuthAndElevation.Y,
+        ray.Distance
+      });
+    }
+  }
+
 }
 
 float ARadar::CalculateRelativeVelocity(const FHitResult& OutHit, const FVector& RadarLocation)

Unreal/CarlaUE4/Plugins/Carla/Source/Carla/Sensor/Radar.h

@@ -81,4 +81,14 @@ private:
 
   UWorld* World;
 
+  struct RayData {
+    float Radius;
+    float Angle;
+    bool Hitted;
+    float RelativeVelocity;
+    FVector2D AzimuthAndElevation;
+    float Distance;
+  };
+  
+  std::vector<RayData> Rays;
 };