internal void DrawBoundingSphere(Matrix view, Matrix projection, 
            GameObject boundingSphereModel)
        {
            Matrix scaleMatrix = Matrix.CreateScale(BoundingSphere.Radius);
            Matrix translateMatrix =
                Matrix.CreateTranslation(BoundingSphere.Center);
            Matrix worldMatrix = scaleMatrix * translateMatrix;

            foreach (ModelMesh mesh in boundingSphereModel.Model.Meshes)
            {
                foreach (BasicEffect effect in mesh.Effects)
                {
                    effect.World = worldMatrix;
                    effect.View = view;
                    effect.Projection = projection;
                }
                mesh.Draw();
            }
        }
 /// <summary>
 /// Allows the game to perform any initialization it needs to before starting to run.
 /// This is where it can query for any required services and load any non-graphic
 /// related content.  Calling base.Initialize will enumerate through any components
 /// and initialize them as well.
 /// </summary>
 protected override void Initialize()
 {
     ground = new GameObject();
     gameCamera = new Camera();
     boundingSphere = new GameObject();
     bullets = new List<Bullet>();
     base.Initialize();
 }