A synthetic acceleration shape bound primitives composing a 3-D scene, and is defined using a group of fundamental shapes arranged to bound the primitives, and for which intersection results for group members yield an ultimate intersection testing result for the synthetic shape, using a logical operator. For example, two or more spheres are used to bound an object so that each of the spheres is larger than a minimum necessary to bound the object, and a volume defined by an intersection between the shapes defines a smaller volume in which the object is bounded. A ray is found to potentially intersect the object only if it intersects both spheres. In another example, an element may be defined by a volumetric union of component elements. Indicators can determine how groups of shapes should be interpreted. Synthetic shapes can be treated as a single element in a graph or hierarchical arrangement of acceleration elements.