Reconstruction of Articulated Objects from a Moving Camera

Many scenes that we would like to reconstruct contain articulated objects, and are often captured by only a single, non-fixed camera. Existing techniques for reconstructing articulated objects either require templates, which can be challenging to acquire, or have difficulties with perspective effects and missing data. In this paper, we present a novel reconstruction pipeline that first treats each feature point tracked on the object independently and incrementally imposes constraints. We make use of the idea that the unknown 3D trajectory of a point tracked in 2D should lie on a manifold that is described by the camera rays going through the tracked 2D positions. We compute an initial reconstruction by solving for latent 3D trajectories that maximize temporal smoothness on these manifolds. We then leverage these 3D estimates to automatically segment an object into piece-wise rigid parts, and compute a refined shape and motion using sparse bundle adjustment. Finally, we apply kinematic constraints on automatically computed joint positions to enforce connectivity between different rigid parts, which further reduces ambiguous motion and increases reconstruction accuracy. Each step of our pipeline enforces temporal smoothness, and together results in a high quality articulated object reconstruction. We show the usefulness of our approach in both synthetic and real datasets and compare against other non-rigid reconstruction techniques.