An interface provided by objects that can be moved geographically. Typically, implementing objects move the entire
object as a whole in response to the methods in this interface. See the documentation for each implementing class to
determine whether the class deviates from this.
A position associated with the object that indicates its aggregate geographic position. The chosen position
varies among implementers of this interface. For objects defined by a list of positions, the reference position
is typically the first position in the list. For symmetric objects the reference position is often the center of
the object. In many cases the object's reference position may be explicitly specified by the application.
the object's reference position, or null if no reference position is available.