"Closest Rotation" Function

Hello Lovelies,

I’m trying to make a function that will evaluate an array of rotations and see which is closest to another given rotation.

I envisage the function taking 2 arguments, the first a single rotation and the second an array of rotations to be compared to. The function would then return the index of the closest rotation in the array.

The problem is, I don’t know where to start with this.

If anyone can help, that would be absolutely marvellous. Anything, even pseudo code would be magnificent.


Here is a way to do it :


int32 GetClosestRotationIndex(FRotator TargetRotation, const TArray<FRotator>& RotationsArray) const;


int32 UMyObject::GetClosestRotationIndex(FRotator TargetRotation, const TArray<FRotator>& RotationsArray) const

	int32 Index = 0;
	float DeltaAngle = FQuat::Error(TargetRotation.Quaternion(), RotationsArray[Index].Quaternion());

	for (int32 i = 0; i < RotationsArray.Num(); i++)
		const  float TempDelta = FQuat::Error(TargetRotation.Quaternion(), RotationsArray*.Quaternion());

		if (DeltaAngle > TempDelta)
			DeltaAngle = TempDelta;
			Index = i;

	return Index;

Awesome, thank you so much @Mhousse1247 , that looks rock solid.

I thought this code as so worthy that I’ve taken the liberty of writing a test for it.


#include "mxbox.h"
#include "AutomationTest.h"
#include "MXBlueprintFunctionLibrary.h"

IMPLEMENT_SIMPLE_AUTOMATION_TEST(FMiscTest, "mxbox.MiscTest", EAutomationTestFlags::ApplicationContextMask | EAutomationTestFlags::ProductFilter)

bool FMiscTest::RunTest(const FString& Parameters)
	TArray<FRotator> RotationArray;
	RotationArray.Push(FRotator(0.f , 0.f  , 0.f));
	RotationArray.Push(FRotator(0.f , 0.f  , 90.f));
	RotationArray.Push(FRotator(0.f , 90.f , 180.f));
	RotationArray.Push(FRotator(90.f, 180.f, 270.f));

	TestEqual(TEXT("Testing GetClosestRotationIndex 0"), UMXBlueprintFunctionLibrary::GetClosestRotationIndex(FRotator(0.f , 11.f , 20.f ), RotationArray), 0);
	TestEqual(TEXT("Testing GetClosestRotationIndex 1"), UMXBlueprintFunctionLibrary::GetClosestRotationIndex(FRotator(0.f , 0.f  , 95.f ), RotationArray), 1);
	TestEqual(TEXT("Testing GetClosestRotationIndex 2"), UMXBlueprintFunctionLibrary::GetClosestRotationIndex(FRotator(0.f , 93.f , 186.f), RotationArray), 2);
	TestEqual(TEXT("Testing GetClosestRotationIndex 3"), UMXBlueprintFunctionLibrary::GetClosestRotationIndex(FRotator(80.f, 180.f, 240.f), RotationArray), 3);

	return true;

Please note, to any passers by, this is my first ever unit test - so please tread with caution (and please feel free to critique)

If anybody needs help implementing this, please shout and I’ll be happy to help.