CoreLocation heading base on back camera (Augmented reality)

Question

I would like to create an augmented reality view that is going to point an object in a direction. However, the CoreLocation heading is not working correctly when you are fac

Answer 1

To save anyone else's time, here's Chee's answer in Swift:

import GLKit    

func headingCorrectedForTilt() -> Float?{
        guard let motion = self.motionManager.deviceMotion else{
            return nil
        }

        let aspect = fabsf(Float(self.view.bounds.width / self.view.bounds.height))
        let projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(45.0), aspect, 0.1, 100)


        let r = motion.attitude.rotationMatrix
        let camFromIMU = GLKMatrix4Make(Float(r.m11), Float(r.m12), Float(r.m13), 0,
                           Float(r.m21), Float(r.m22), Float(r.m23), 0,
                           Float(r.m31), Float(r.m32), Float(r.m33), 0,
                           0,     0,     0,     1)

        let viewFromCam = GLKMatrix4Translate(GLKMatrix4Identity, 0, 0, 0);
        let imuFromModel = GLKMatrix4Identity
        let viewModel = GLKMatrix4Multiply(imuFromModel, GLKMatrix4Multiply(camFromIMU, viewFromCam))
        var isInvertible : Bool = false
        let modelView = GLKMatrix4Invert(viewModel, &isInvertible);
        var viewport = [Int32](count:4,repeatedValue: 0)

        viewport[0] = 0;
        viewport[1] = 0;
        viewport[2] = Int32(self.view.frame.size.width);
        viewport[3] = Int32(self.view.frame.size.height);

        var success: Bool = false
        let vector3 = GLKVector3Make(Float(self.view.frame.size.width)/2, Float(self.view.frame.size.height)/2, 1.0)
        let calculatedPoint = GLKMathUnproject(vector3, modelView, projectionMatrix, &viewport, &success)

        return success ? atan2f(-calculatedPoint.y, calculatedPoint.x) : nil
    }