Vector3.Angle returning wrong values for vectors with small components

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I tried to get the angle between two Vector3's using Vector3.Angle and got a return value I didn't expect.

The two vectors where (1, 0, 0) and (0.00001, 0, 0) and the angle between the two should obviously be 0. However, Vector3.Angle returns 90.

This isn't related to the length difference of the vectors, Vector3.Angle also reports the angle between (0.00001, 0, 0) and itself as 90. On the other hand, the difference between (1000000, 0, 0) and itself or (1, 0, 0) is reported correctly as 0.

Is this related to the algorithm used by Vector3.Angle or a bug? The documentation doesn't say anything about it expecting only vectors in a specific range or only normalized ones.

Answer 1

Best Answer

Answer by Adrian · Aug 26, 2011 at 11:24 AM

Normalizing probably is the issue here. The documentation on Vector3.Normalize states:

If the vector is too small to be normalized a zero vector will be returned.

Vector3.Angle probably normalizes the input vectors, calculating the angle between (1, 0, 0) and (0, 0, 0). Vector3.Angle also seems to return 90 when either of its input vectors has zero length.

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$$anonymous$$ · Dec 16, 2013 at 04:42 PM 0

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In case anyone else looking for more details I've found out that Unity zeros all vectors shorter than 0.05f.

Just try this: Debug.Log ("Vector2.right 0.049 = " + Vector2.right 0.049f); results in a zeroed vector

chris.weigle · Dec 16, 2013 at 04:48 PM 1

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No, that's just due to the default ToString format for float.

Try:

Debug.Log ("Vector2.right 0.049 = " + (Vector2.right 0.049f).ToString("R"));

$$anonymous$$ · Dec 16, 2013 at 06:48 PM 0

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thanks for that, was so disappointed with unity :)

Answer 2

Answer by elliselkins · Apr 21, 2016 at 08:23 PM

I ran into this problem as well, so I wrote my own angle functions.

     //This returns the angle in radians
     public static float AngleInRad(Vector3 vec1, Vector3 vec2)
     {
         return Mathf.Atan2(vec2.y - vec1.y, vec2.x - vec1.x);
     }
 
     //This returns the angle in degress
     public static float AngleInDeg(Vector3 vec1, Vector3 vec2)
     {
         return AngleInRad(vec1, vec2) * 180 / Mathf.PI;
     }

See Atan2 for more details.

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VirtualSUN · Nov 21, 2018 at 08:23 AM 0

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Ok, but something going wrong: A & B is a Vector2. if we do this Mathf.Atan2(B.y - A.y, B.x - A.x) * 180 / Mathf.PI then we got that A (1.0, -1.0) B (-1.0, 1.0) = 135

???

juanitogan VirtualSUN · Apr 16 at 11:00 PM 0

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Mathf functions return polar coordinates instead of game coordinates.

VirtualSUN juanitogan · Apr 16 at 11:57 PM 0

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But the angle between A (1.0, -1.0) B (-1.0, 1.0) = 180

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Bunny83 VirtualSUN · Apr 17 at 11:34 AM 1

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This answer may be misleading since it expects two 2d position vectors as inputs, not two direction vectors like Vector3.Angle. This method here also just calculates the mathematical counter clockwise angle between the worldspace x axis and the connection vector between the two points. This is fundamentally something different.

The result of 135 is right for the two point A=(1.0, -1.0) and B=(-1.0, 1.0). The actual direction vector will be (-2, 2) which is 135° away from the x axis.

Of course as i said this answer is providing a solution for a completely different / unrelated problem.

edit
Note that Vector3.Angle actually expects two direction vectors and it's implemented like this

Vector3.Angle returning wrong values for vectors with small components

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