[API Noob] How to calculate a relative angle in CPP/UE4

[Nsomnia]

@Mlody "Swidwin";527685

I’m not clearly sure what you trying to achieve there but

toTarget = target.position - submarine.position;

relativeHeading = submarine.Heading.Dot(target.heading); // heading is normalized vector pointing in heading direction 

if(toTarget.Dot(submarine.heading) > 0 &&  (relativeHeading < -0.95)) // acos(0.95) = 18 degs
{
  target is ahead of submarine
}
else
{
  target is not ahead 
}

@ExtraLifeMatt;527267

This should be doable, I’ll use the names you have in your image.

FVector LineOfSight = SubmarinePosition - TargetPosition;
float BowAngleInDegrees = FMath::RadiansToDegrees(Acos(FVector::DotProduct(Target.Forward, LineOfSight))); // Dot product describes the angle between Target and LineOfSight, taking the Arc Cosine gives you the actual angel in radians (0 - 2PI), we then convert that to degrees.
if (FVector::DotProduct(Target.Right, LineOfSight) < 0.0f) // We need one more dot product to actually figure out our winding
{
    BowAngleInDegrees *= -1;
}

That should give you a relative turning angle in degrees.

So I did your example exactly and got these results with the following code

.H

public:

	//Functions
	UFUNCTION(BlueprintCallable, Category = "cpp")
	static float AngleOnBow(APawn* TargetShip, APawn* PlyrShip);

.CPP

float UBPFuncLib_TDChelper::AngleOnBow(APawn* TargetShip, APawn* PlyrShip)
{
	FVector LineSight = (PlyrShip->GetActorLocation() - TargetShip->GetActorLocation());
	float BowAngleInDeg = FMath::RadiansToDegrees(FGenericPlatformMath::Acos(FVector::DotProduct(TargetShip->GetActorForwardVector(), LineSight)));
	
	if (FVector::DotProduct(TargetShip->GetActorRightVector(), LineSight) < 0.0f) // We need one more dot product to actually figure out our winding
	{
		BowAngleInDeg *= -1;
	}
	return BowAngleInDeg;
}

But then I normalize it and it APPEARS to work. Will get back with more details.

float UBPFuncLib_TDChelper::AngleOnBow(APawn* TargetShip, APawn* PlyrShip)
{
	FVector LineSight = (PlyrShip->GetActorLocation() - TargetShip->GetActorLocation());
	LineSight.Normalize();
	float BowAngleInDeg = FMath::RadiansToDegrees(FGenericPlatformMath::Acos(FVector::DotProduct(TargetShip->GetActorForwardVector(), LineSight)));
	
	if (FVector::DotProduct(TargetShip->GetActorRightVector(), LineSight) < 0.0f) // We need one more dot product to actually figure out our winding
	{
		BowAngleInDeg *= -1;
	}
	return BowAngleInDeg;
}

What would be the best way to set it to 180d if its say 0.1 to - 0.1 (Your directly in the front of the ship, it should still return 180 not 0)

I think this is workable regardless! Thank you!