Blocks World Revisited

Since most current scene understanding approaches operate either on the 2D image or using a surface-based representation, they do not allow reasoning about the physical constraints within the 3D scene. Inspired by the "Blocks World" work in the 1960's, we present a qualitative physical representation of an outdoor scene where objects have volume and mass, and relationships describe 3D structure and mechanical configurations. Our representation allows us to apply powerful global geometric constraints between 3D volumes as well as the laws of statics in a qualitative manner. We also present a novel iterative "interpretation-by-synthesis" approach where, starting from an empty ground plane, we progressively ``build up'' a physically-plausible 3D interpretation of the image. For surface layout estimation, our method demonstrates an improvement in performance over the state-of-the-art geometric context algorithm. But more importantly, our approach automatically generates 3D parse graphs which describe qualitative geometric and mechanical properties of objects and relationships between objects within an image.

• Static Equilibrium: Under the static world assumption, the forces and torques acting on a block should cancel out (Newton's first law).
• Support Force Constraint: A supporting object should have enough strength to provide contact reactionary forces on the supported objects.
• Volumetric Constraints: All the objects in the world must have finite volumes and cannot inter-penetrate each other.