Module 

Header 
/Engine/Source/Runtime/Core/Public/Math/Vector.h 
Include 
#include "Math/Vector.h" 
Source 
/Engine/Source/Runtime/Core/Private/Math/UnrealMath.cpp 
FRotator ToOrientationRotator() const
Return the FRotator orientation corresponding to the direction in which the vector points. Sets Yaw and Pitch to the proper numbers, and sets Roll to zero because the roll can't be determined from a vector.
FRotator from the Vector's direction, without any roll.