I am trying to get a sprite to position itself at the center of the screen but nothing seems to be working for me. I'm trying

Viewport viewport = graphics.GraphicsDevice.Viewport;
logoPosition = new Vector2((viewport.Width - towerImage.Width) / 2,
                           (viewport.Height - towerImage.Height) / 2);

and

spriteBatch.Draw(towerImage, centre, null, Color.White, 0, baseOrigin, 1.0f, SpriteEffects.None, 0);

This is my first time using XNA and I don't really have a clue what I'm doing.