Cardboard without gyroscope

I recently bought a Cardboard to play around with the possibilities of VR in Unity3D. But then i realized, that my smartphone doesn't have a gyroscope... holy crap... So, what now? Just find a way to get it working without it :) If you have a smartphone with a compass and a accelerometer module, then this is for you.

Just create a new project and download the Google VR unitypackage from their GitHub page. Just click on the Download button on the right side, and choose Open with unity editor in the download options. Then just click on import.

Then create a new empty GameObject, name it Player and drag the GVRMain Prefab from the Legacy folder onto it.

Select the Head object from the GVRMain object and uncheck Track Rotation and Track Position.

Next, create a new C# script and name it VRController and drag it onto the Player GameObject.

We need to start the compass and the location services in the Start function

using UnityEngine;
using System.Collections;

public class VRController : MonoBehaviour {
    
    void Start() {
        Input.compass.enabled = true;
        Input.location.Start();
    }

}

We also need a Vector3 to store the accelerometer values and a float to store the current compass heading.

    Vector3 acceleration = Vector3.zero;
    float heading = 0f;

Since the compass and the accelerator are quite choppy, we need to smooth the calculation, and therefore we need a rotationspeed float.

    public float rotationSpeed = 8f;

So, our script till now:

using UnityEngine;
using System.Collections;

public class VRController : MonoBehaviour {

    public float rotationSpeed = 8f;

    Vector3 acceleration = Vector3.zero;
    float heading = 0f;

    void Start() {
        Input.compass.enabled = true;
        Input.location.Start();
    }

}

Next step is our Update function. In there, we are setting the current acceleration and the current compass heading and then we set the rotation of our Player GameObject to the calculated rotation

    void Update() {
        SetAcceleration();
        SetCompassHeading();

        transform.eulerAngles = SetRotation();
    }

    void SetAcceleration() {

    }

    void SetCompassHeading() {

    }

    Vector3 SetRotation() {

    }

In the SetAcceleration function, we are getting the current acceleration from the Input and Lerp the previously stored acceleration to the new value

    void SetAcceleration() {
        Vector3 _acceleration = Input.acceleration;

        acceleration.x = Mathf.Lerp(acceleration.x, _acceleration.x, Time.deltaTime * rotationSpeed);
        acceleration.y = Mathf.Lerp(acceleration.y, _acceleration.y, Time.deltaTime * rotationSpeed);
        acceleration.z = Mathf.Lerp(acceleration.z, _acceleration.z, Time.deltaTime * rotationSpeed);
    }

In the SetCompassHeading function, we do the same, but just for the float value of the compass heading, and we are using LerpAngle here, because if we used Lerp, we would get wrong angles, if the value if going greater then 180 degrees.

    void SetCompassHeading() {
        float _heading = Input.compass.trueHeading;

        heading = Mathf.LerpAngle(heading, _heading, Time.deltaTime * rotationSpeed);
    }

In the SetRotation function, we are calculating the x and z angles and return the Vector3 object for the transform's eulerAngles property.

    Vector3 SetRotation() {
        float _rotationX = Mathf.Atan2(acceleration.z, acceleration.y);
        float _magnitudeYZ = Mathf.Sqrt(Mathf.Pow(acceleration.y, 2) + Mathf.Pow(acceleration.z, 2));
        float _rotationZ = Mathf.Atan2(acceleration.x, _magnitudeYZ);

        float _angleX = _rotationX * (180f / Mathf.PI) + 90f;
        float _angleZ = -_rotationZ * (180f / Mathf.PI);

        return new Vector3(_angleX, -(_angleZ - heading), 0f);
    }

So, our complete script should look like this

using UnityEngine;
using System.Collections;

public class VRController : MonoBehaviour {

    public float rotationSpeed = 8f;

    Vector3 acceleration = Vector3.zero;
    float heading = 0f;

    void Start() {
        Input.compass.enabled = true;
        Input.location.Start();
    }

    void Update() {
        SetAcceleration();
        SetCompassHeading();

        transform.eulerAngles = SetRotation();
    }

    void SetAcceleration() {
        Vector3 _acceleration = Input.acceleration;

        acceleration.x = Mathf.Lerp(acceleration.x, _acceleration.x, Time.deltaTime * rotationSpeed);
        acceleration.y = Mathf.Lerp(acceleration.y, _acceleration.y, Time.deltaTime * rotationSpeed);
        acceleration.z = Mathf.Lerp(acceleration.z, _acceleration.z, Time.deltaTime * rotationSpeed);
    }

    void SetCompassHeading() {
        float _heading = Input.compass.trueHeading;

        heading = Mathf.LerpAngle(heading, _heading, Time.deltaTime * rotationSpeed);
    }

    Vector3 SetRotation() {
        float _rotationX = Mathf.Atan2(acceleration.z, acceleration.y);
        float _magnitudeYZ = Mathf.Sqrt(Mathf.Pow(acceleration.y, 2) + Mathf.Pow(acceleration.z, 2));
        float _rotationZ = Mathf.Atan2(acceleration.x, _magnitudeYZ);

        float _angleX = _rotationX * (180f / Mathf.PI) + 90f;
        float _angleZ = -_rotationZ * (180f / Mathf.PI);

        return new Vector3(_angleX, -(_angleZ - heading), 0f);
    }

}

With this done, we are able to control the cardboard without a gyroscope, just with a compass and an accelerometer module. It's not as exact as a gyroscope, but at least, it's working. You can optimize this little module with a detector, if the device has a gyroscope, and if yes, you can disable the manual calculation and enable the track position and rotation booleans from the GVRHead again.