Object does not rotate in the correct direction from Atan2 to Quaternion

Question

I am trying to rotate an object on its z axis, given a point I calculated at an angle with Atan2 function. Then I create a Quaternion to enter it in the rotation of the object. However, it does not rotate in the supposedly correct direction. If I diagram the angles given by the Atan2 functions, I visualize a clockwise system of angles, but if I diagram the angles that should be so that my object is rendered in the correct direction, I visualize an anti-clockwise system. The solutions creating a dictionary with the values received by the Atan2 function as keys and their values are the angles with which the object will rotate the correct direction. But I still don't understand what is happening. I hope someone can help me understand it because there is no worse solution than the one that solves but without knowing what is happening.

public class ArrowMovement : MonoBehaviour
{
    public Vector2Variable currentPlayerDirection;
    public Vector3Variable currentPlayerPosition;
    public InputAxis inputAxis;

    private float anglePassed;
    private Dictionary<float, float> realAngles = new Dictionary<float, float>();

    void Awake()
    {
        realAngles.Add(-135, -135);
        realAngles.Add(-90, 180);
        realAngles.Add(-45, 135);
        realAngles.Add(0, 90);
        realAngles.Add(45, 45);
        realAngles.Add(90, 0);
        realAngles.Add(135, -45);
        realAngles.Add(180, -90);
    }

    void Update()
    {
        Vector3 offsetVector = new Vector3(0.2f, 0.05f, 0);
        transform.position = currentPlayerPosition.Value;

        // Rotation
        float angle = Mathf.Atan2(inputAxis.horizontal, inputAxis.verticall) * Mathf.Rad2Deg;
        Quaternion rotation = Quaternion.Euler(0, 0, realAngles[angle]);
        transform.rotation = rotation;
    }
}

score 1 · Answer 1 · answered Dec 08 '19 at 01:33

1

Creating a dictionary is not the best way because it does not take into account the angles between the ones you set so to convert from one diagram to the other I would create a function that looks like:

float ChangeAngleDiagram(float angle) {
    return -(angle + 90f)+180;
}

answered Dec 08 '19 at 01:33

Anis Brachemi

71
6

You are right and thank you very much for the function. I would still have the doubt as to why this behavior happens. – user3324336 Dec 08 '19 at 04:48

score 1 · Accepted Answer · answered Feb 11 '20 at 07:10

First of all, you should know what inputAxis is. I can guess from your diagram that you expect that for inputAxis.verticall == 0 the angle must be 0. Let's look at Mathf.Athan2(y,x) - it is equivalent to arctan(y/x), so result will be zero only when y is zero. But, in your code Mathf.Atan2(inputAxis.horizontal, inputAxis.verticall) will give 0 when inputAxis.horizontal == 0 - it is vertical direction (your first diagram).

Second issue - wrong rotation direction. This can happen when one of the input axes is inverted. Probably, inputAxis is measured in a different coordinate system relative to your object, i.e. Z of your object is -Z of your inputAxis. Anyway, inputAxis.verticall can be inverted

float angle = Mathf.Atan2(inputAxis.horizontal, -inputAxis.verticall) * Mathf.Rad2Deg;

Also, you should avoid solving a simple geometric problem by "creating a dictionary" or anything like that. Even if you don't know how inputAxis works and result is wrong - make two step to fix it: 1. fix rotation direction - just invert the angle Quaternion.Euler(0, 0, -angle); 2. fix the zero position - add some static rotation. It is 90 deg in your case Quaternion.Euler(0, 0, 90 - angle). And it is the second way to solve the problem.

Object does not rotate in the correct direction from Atan2 to Quaternion

2 Answers2