SceneKit, projecting a node along camera orientation

Question

With SceneKit, I see that a node, to which a camera is attached, has a eulerAngles (SCNVector3 of radian angles) and orientation (SCNQuaternion)

My cameraNode is at 0,0,0 and can change its orientation at any moment.

I need to do hitTestWithSegmentFromPoint... toPoint...

fromPoint is always known.

But I need to project, based on camera orientation a far away point that lies in the line of the camera.

My mind hasn't grabbed quaternions properly yet, and I'm not getting anywhere based on eulerAngles.

Answer 1

Using some linear algebra

func findNextPoint(p0: SCNVector3, direction: SCNVector3) -> SCNVector3{

    var x = Float()
    var y = Float()
    var z = Float()
    let t = 100 as Float

    x = p0.x + t * direction.x
    y = p0.y + t * direction.y
    z = p0.z + t * direction.z

    let result = SCNVector3Make(x, y, z)
    return result

}

This uses p0 as a starting point to, then, find the next point you want on a given direction. t is the length of the vector, or the distance you want to travel from p0.

To find the direction the camera is pointing, you must get its rotation and multiply by a Rotation Matrix.

func calculateCameraDirection(cameraNode: SCNNode) -> GLKVector3 {

    let x = -cameraNode.rotation.x
    let y = -cameraNode.rotation.y
    let z = -cameraNode.rotation.z
    let w = cameraNode.rotation.w

    let cameraRotationMatrix = GLKMatrix3Make(cos(w) + pow(x, 2) * (1 - cos(w)),
        x * y * (1 - cos(w)) - z * sin(w),
        x * z * (1 - cos(w)) + y*sin(w),

        y*x*(1-cos(w)) + z*sin(w),
        cos(w) + pow(y, 2) * (1 - cos(w)),
        y*z*(1-cos(w)) - x*sin(w),

        z*x*(1 - cos(w)) - y*sin(w),
        z*y*(1 - cos(w)) + x*sin(w),
        cos(w) + pow(z, 2) * ( 1 - cos(w)))

    let cameraDirection = GLKMatrix3MultiplyVector3(cameraRotationMatrix, GLKVector3Make(0.0, 0.0, -1.0))

    return cameraDirection

}

You then just need to perform the hitTest using both coordinates. In this case I used rayTestWithSegmentFromPoint:ToPoint , but you may use any other kind of test there, such as hitTestWithSegmentFromPoint:toPoint: .

func raycastTest(cameraDirection: GLKVector3) -> SCNVector3{

    let nextPoint = findNextPoint(cameraNode.position, direction: SCNVector3Make(cameraDirection.x, cameraDirection.y, cameraDirection.z))
    let hitTest = sceneView.scene!.physicsWorld.rayTestWithSegmentFromPoint(cameraNode.position, toPoint: nextPoint, options: nil)

    if hitTest.count > 0 {
        return (hitTest.first?.worldCoordinates)!
    }else{
        return nextPoint
    }
}