XNA Billboard sprite to camera plane

I got a camera set up with

        _aspectRatio = device.Viewport.Aspe开发者_StackOverflow中文版ctRatio;
        _projectionMatrix = Matrix.CreatePerspectiveFieldOfView(MathHelper.ToRadians(90.0f),_aspectRatio,0.1f,10000.0f);

The view matrix get set with the Update, and the _position is set by a rotation defined in rotation.

private void Update()
{
    _viewMatrix = Matrix.CreateLookAt(_position, _lookAt, Vector3.Up);
}

public void Rotate(float angle)
{
    rotation += angle;
    _position = Vector3.Transform(_position, Matrix.CreateRotationY(angle));
    Update();
}

To set the sprite in the field, i use this code:

        _effect.Parameters["xWorld"].SetValue(Matrix.CreateRotationY(camera.rotation) * PositionMatrix);
        _effect.Parameters["xView"].SetValue(camera.ViewMatrix);
        _effect.Parameters["xProjection"].SetValue(camera.ProjectionMatrix);
        _effect.Parameters["xTexture"].SetValue(_texture);

It is working, the sprite is looking at the camera perpendiculair with the camera plane. Problems are coming when the camera position vector is changed, the sprite is keeping the initial angle and I don't know where I can calculate the changed Y rotation for the sprite.

The solution was that I took the y rotation in the camera class. In that class I had a method where I could see the y rotation.