Normal vector of a Raycast 2D wrong ?

Hi everyone,

It's my first time posting here because after spending the whole day on a problem, I just can't find an answer by myself.
Here is my issue:


What i try: I would like my skateboarder to rotate to match the inclined plane and the ground.
Current code:
To do so, i use a Raycast that points the ground (the white line) and check the normal and calculate the angle I need to rotate.

Code (CSharp):

1. private void FixedUpdate()
2.     {
3.         Vector2 raycastOrigin = _rigidbody.position + (Vector2) transform.right * 0.16f + (Vector2)transform.up * 0.1f;
4.         Debug.DrawRay(raycastOrigin, -transform.up);
5.         RaycastHit2D hit = Physics2D.Raycast(raycastOrigin, -transform.up, 1f, LayerMask.GetMask("Ground"));
6.         if (hit.collider != null)
7.         {
8.             Debug.DrawLine(hit.point, hit.normal, Color.yellow, 10f);
9.             float angle = Vector2.Angle(hit.point, hit.normal);
10.             Debug.Log("angle = " + angle);
11.         }
12.     }

But it seems like the normal of my Raycast is always the same position as you can see with the yellows lines and I can't explain why this one in particular. It moves when the skater is on the inclined plane, but same behaviour.

What I expect: I would like to have something that tells me the angle of the ground, for example 180° at first and then 160° or 200° (depending on which side)

Any help would be much appreciated !

Thanks by advance

PS: don't judge my drawing skills it's only to learn Unity haha

 

I think your raycast is working fine. But you're using Debug.DrawLine to draw the yellow line, and that expects two world space coordinates. You're giving it a world space coordinate (the hit point) and a direction vector (the normal). Try using Debug.DrawRay instead for that line of code (line 8 in your snippet).

Code (CSharp):

1. Debug.DrawRay(hit.point, hit.normal, Color.yellow, 10f);

Also your use of Vector2.Angle has a similar problem. Vector2.Angle expects two direction vectors. You're giving it one world position (the hit point) and one direction vector (the normal). What you probably want is

Code (CSharp):

1. float angle = Vector2.Angle(Vector2.up, hit.normal)

which will give you the angle between straight up and your raycast normal. That will return 0 for flat ground, and a non-zero angle for slanted ground.

 

Thank you very much, I found the solution before your edit

Here is what I did:

Code (CSharp):

1. private void FixedUpdate()
2.     {
3.         Vector2 raycastOrigin = _rigidbody.position + (Vector2) transform.right * 0.16f + (Vector2)transform.up * 0.1f;
4.         Debug.DrawRay(raycastOrigin, -transform.up);
5.         RaycastHit2D hit = Physics2D.Raycast(raycastOrigin, -transform.up, 1f, LayerMask.GetMask("Ground"));
6.         if (hit.collider != null)
7.         {
8.             Debug.DrawRay(hit.point, hit.normal, Color.yellow, 10f);
9.             float angle = Vector2.Angle(transform.right, hit.normal) - 90;
10.             Debug.Log("angle = " + angle); // 0 on ground, 18.2 on inclined plane
11.         }
12.     }

I didn't understand very well that there is a difference between Vector2 that are "points" and other that are directions.
I wonder why both of these notions are stored in the same object (Vector2) instead of making Point2D and Direction2D, I must check the basic maths now haha

Thanks again !

 

If you think about it they are the same thing. A world point is a "direction" vector that starts from the origin (coordinates [0, 0]). It's basically a matter of where the "origin" of the vector is when you think about it. "direction" vectors are generally thought about as originating from some place other than the origin (such as your player position), whereas "position" vectors are always thought about as originating from the origin. They are really the same though.

 

Oh that makes sense, the x and y values depend on the reference. If we know the origin we can know the direction we're pointing at.

Thank you for your time and your quick answer