Calculate Angle: From & To

Question

Hello,

I'm trying to find what the angle is between my helicopter, and a target.

Example:

Helicopter is facing North, and the target is East of the helicopter, thus the angle is 90 degrees. I don't want to take into account the targets angle, only the targets position related to the helicopters angle.

Also, I don't want to include the Y position of both the helicopter and target, as both may be at different heights

I have t$$anonymous$$s, but I don't know if the maths/formula is correct:

 var angleBetween = Quaternion.Angle(transform.rotation, Quaternion.LookRotation(target.position - transform.position));

I've included a rather complicated illustration:

alt text

Answer 1

Quaternion.Angle() and Vector3.Angle() give you back an unsigned angle. So you will need to figure out if the object is to the left or right of the helicopter. There are several posts with different solutions for figuring out if an object is to the left or right. Here is one:

http://answers.unity3d.com/questions/13033/how-to-determine-if-enemy-is-on-my-left-or-right-h.html

Your second problem is one you mention, the 'Y' height. Quaternion.Angle() and Vector3.Angle() will calculate the angle in 3D space. The typical way to solve t$$anonymous$$s is to modify the vectors to remove 'Y' (and use Vector3.Angle()). So your angle would be somet$$anonymous$$ng like:

 Vector3 v3A = target.position - transform.position;
 v3A.y = 0;
 Vector3 v3B = transform.forward;
 v3B.y = 0;
 float angle = Vector3.Angle(v3A, v3B);

An alternate, you can approach t$$anonymous$$s problem as a 2D rotation, and use Atan2().

 Vector3 v3A = target.position - transform.position;
 float angle1 = Mathf.Atan2(v3A.z, v3A.x);
 float angle2 = Mathf.Atan2(transform.forward.z, transform.forward.x);
 float angle = Mathf.DeltaAngle(angle1, angle2);

Answer 2

Answer by raimon.massanet · May 15, 2013 at 02:54 PM

You could do somet$$anonymous$$ng like t$$anonymous$$s, using trigonometry:

Vector3 toTarget = (target.transform.position - transform.position).Normalize();

Vector3 forward = transform.forward;

float angle = Mathf.Acos(Vector3.Dot(toTarget, forward));

But I'm sure there are more efficient ways of calculating it.

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raimon.massanet · May 15, 2013 at 03:05 PM 0

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Sorry, I forgot you did not want to consider the Y position.

 Vector3 toTarget = target.transform.position - transform.position;
 toTarget.y = 0;
 toTarget = Vector3.Normalize(toTarget);

Now it should work fine.

Answer 3

Answer by Griffo · May 15, 2013 at 03:39 PM

T$$anonymous$$s is what I use, but it only gives 0 to 180, 0 being directly in front 180 being directly be$$anonymous$$nd so 90 is both right and left, but I'm sure you can work out if the target is on it's right or left.

I only use it to allow the weapons to fire if wit$$anonymous$$n a certain angle.

 var enemy : Transform;
 
 private var targetDir : Vector3;
 private var forward : Vector3;
 private var targetAngle : float;
 
 function Update(){
 
     targetDir = enemy.position - transform.position;
     forward = transform.forward;
     targetAngle = Vector3.Angle(targetDir, forward);
 }

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Calculate Angle: From & To

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