Libgdx OrthographicCamera - How to set graphical objects always to center?

I have defined VIEWPORT_WIDTH and VIEWPORT_HEIGHT values. After that I would like to set all my objects to the center of this area. By default I see all of my graphical items, sprites at the left corner. I use now this code:

        camera = new OrthographicCamera(VIEWPORT_WIDTH, VIEWPORT_HEIGHT);
        camera.position.set(camera.viewportWidth/2f, camera.viewportHeight/2f, 0);

It is a complex object(It is from lines and circles), drawed by ShapeRenderer.
How can I set “always center”?