Adding random noise to a direction vector

Questions & Answers
1

Hi guys, this should be a simple one:
I have defined this direction vector:

(vector3) direction = targetVector - transform.position;
direction.Normalize();

Now, how would one add a random noise to this direction, expressed as min and max ANGLES?
Should I convert this vector to an angle in degrees, add the noise and then back to normalized vector?

Thank you for the assist!

2

To further illustrate what is meant to be done here, here is an example.
A bullet from a high speed, low accuracy machine gun is being fired. The base direction is 100% accurate, but in order to reflect the low accuracy of each projectile a randomization of their direction is needed.

Currently, the projectiles are moving using:

transform.position += direction * projetileSpeed;

What is needed in this case is a way to add a specific angular modifier to the direction vector.

3

Maybe to that targetVector, you could add in a small amount of X and Y, in order to make it slightly deviate?

For instance:

targetVector += transform.up * Random.Range(-randAmt, randAmt) + transform.right * Random.Range(-randAmt, randAmt);

With randAmt being a float value that you can set.

4

So i guess you want something like this, right. I just added the C# translation. You can simply do

dir = GetPointOnUnitSphereCap(dir, 10f);

This will add randomly up to 10° variation to the given direction.

5

Use this function:

direction += AddNoiseOnAngle (0, 30);

[...]

Vector3 AddNoiseOnAngle ( float min, float max)  {
 // Find random angle between min & max inclusive
 float xNoise = Random.Range (min, max);
 float yNoise = Random.Range (min, max);
 float zNoise = Random.Range (min, max);

// Convert Angle to Vector3
 Vector3 noise = new Vector3 ( 
   Mathf.Sin (2 * Mathf.Pi * xNoise /360), 
   Mathf.Sin (2 * Mathf.Pi * yNoise /360), 
   Mathf.Sin (2 * Mathf.Pi * zNoise /360)
 );
   return noise;
   }

This will return a Vector3 whos values are between -1 and 1 inclusive.

6

Thank you for the function. I implemented as follows:
(for some reason I could not use Mathf.Pi).

Vector3 AddNoiseOnAngle ( float min, float max)  {
	float xNoise = Random.Range (min, max);
	float yNoise = Random.Range (min, max);
	float zNoise = 0;

	// Now get the angle between w.r.t. a vector 3 direction
	Vector3 noise = new Vector3 (
		Mathf.Sin (2f * 3.1415926f * xNoise / 360), 
		Mathf.Sin (2f * 3.1415926f * yNoise / 360), 
		                0
	                );
	return noise;

}

At a first glance this appears to work, but the output angles do not seem to be proportionally related to the noise factor added - adding 30 or 3000 yields pretty much the same result (and the deviation never appears to be greater than 45 degrees).

7

PI not Pi

8

Unity contains Mathf.PerlinNoise.