  Collision sequences are commonly used in games and entertainment to add drama
and excitement. Authoring even two body collisions in the real world can be
difficult, as one has to get timing and the object trajectories to be correctly
synchronized. After tedious trial-and-error iterations, when objects can
actually be made to collide, then they are difficult to capture in 3D. In
contrast, synthetically generating plausible collisions is difficult as it
requires adjusting different collision parameters (e.g., object mass ratio,
coefficient of restitution, etc.) and appropriate initial parameters. We
present SMASH to directly read off appropriate collision parameters directly
from raw input video recordings. Technically we enable this by utilizing laws
of rigid body collision to regularize the problem of lifting 2D trajectories to
a physically valid 3D reconstruction of the collision. The reconstructed
sequences can then be modified and combined to easily author novel and
plausible collisions. We evaluate our system on a range of synthetic scenes and
demonstrate the effectiveness of our method by accurately reconstructing
several complex real world collision events.
