1. A non-transitory computer-readable storage medium encoded with a computer-readable data structure for describing an object and a three dimensional volume defining an activation condition of the object, the data structure readable by a computer processor to display the object, the data structure comprising: at least one object markup language element, the object markup language element defining an object to be activated; a plurality of object tags associated with the object markup language element wherein the plurality of object tags describe the object defined by the object element; a plurality of coordinate markup language elements, each coordinate markup language element defining a three dimensional coordinate in a three dimensional space; and a plurality of region tags, comprising a tag for each coordinate markup language element, wherein the region tags describe a three dimensional volume defining the activation condition of the object.