Péter Borosán Rutgers University Doug DeCarlo Rutgers University Andrew Nealan Rutgers University Yotam Gingold George Mason University Ming Jin Rutgers University RigMesh: Automatic Rigging for Part- Based Shape Modeling and Deformation

This Game Is Rigged! Sketch-based tools like Teddy (1999) have been around for many years. While these tools make modeling much easier, they do nothing to facilitate rigging, establishing the underlying skeleton of joints (nodes) and bones (edges). Skinning, the association of the visual representation of the character’s surface with the joints, is also a labor-intensive task.

Rigging The System This research unites modeling, rigging, and skinning into a single tool, allowing the user to interactively re-model, re-rig, and re-skin at any point in the process.

Decomposing The Silhouette From a user’s 2D sketch, the system generates axes that will be used to determine the 3D skeleton and surfaces. First, the user draws the 2D silhouette of the shape. Second, a Chordal Axis Transform is used to find the midpoints of chords of tangency for circumscribed disks within the shape. Third, the midpoints are smoothed into axes, with (green) junction triangles exploiting symmetries where three axes converge and (yellow) rectangular regions connecting some junction triangles. Finally, the junction triangles and connecting rectangles are merged into connecting regions; everything else is considered “cylindrical”.

Generating The Surface The 3D grid is generated from the decomposed 2D silhouette. Generalized cylinders are easily generated from the 2D “cylindrical regions”. Neighboring generalized cylinders are connected with triangle strips. The boundary vertices of the triangle strips are then used to generate a primitive grid across the connecting regions. A least- squares method is applied to smooth the entire grid.

Generating The Skeleton The connecting regions and cylindrical regions are used to determine the skeletal structure. Trapezoids are fit to the cylindrical regions, with a bone corresponding to the central axis of each trapezoid. A joint is added to the center of each joint triangle, and a bone emanates from that joint through the center of each side. Short bones inside connecting regions are collapsed in order to eliminate redundant degrees of freedom for controlling the shape. Skin weights are calculated to determine the extent to which vertices on the 3D surface are affected by the various bones.

Interactive Merging Three means of merging 3D models are provided. Snapping Join two skeletons by making their two joints coincide. Splitting Insert a joint in the middle of one skeleton’s bone in order to create a bone between it and another skeleton’s joint. Connecting Create a new bone joining the joints of two separate skeletons.

Sample Models & Poses