Geometric Hierarchy Tracking

Geometric Hierarchy (GeoH) tracking involves one or more of these three elements:

  • Geometry tracking: tracking based directly on meshes
  • Hierarchical tracking: a rig becomes animated, maintaining specific relationships between the parts.
  • Mesh Deformation: the tracked object hierarchy(rig) acts as "bones" to deform a mesh.

While GeoH tracking can involve tracking geometry directly, GeoH tracking also commonly uses supervised trackers, which don't require that you have an existing reference mesh and can be used under very adverse conditions. It can be used by itself, or in combination with standard SynthEyes moving-object tracks for secondary tracking.

Here are some examples where we might apply geometric hierarchy tracking:

  • A person, with a body connected to each upper arm connected to a forearm connected to the hand then to fingers, etc while separately the body connects to each thigh then to a calf then to a foot;
  • Facial parts (eyebrows, chin, cheeks, lips) deforming into a sequence of expressions;
  • Secondary animations such as jiggly body parts;
  • Similarly for animals: cats, horses, birds, etc;
  • Machines, such as a car with doors and hood that open and wheels that turn and bounce up and down;
  • Objects moving with limited degrees of freedom, such as rolling balls;
  • Perhaps a hierarchy of a tree blowing in the wind.

GeoH geometry tracking is based on the shape of the mesh; the mesh is repositioned and deformed continually over the duration of the shot to match the imagery. In that way it's an elaboration on planar tracking, except that it works for any kind of mesh, and it is designed to handle very large meshes. Self-occlusion and occlusion by other objects is taken into account.

Whether tracked by geometry or regular trackers, if a mesh is affected by multiple parts of the hierarchy, the mesh will be deformed to match the motion of the hierarchy. A single mesh model of an actor may be deformed by a complete hierarchy to match the live action shot.

GeoH tracking preserves the exact dimensions and interrelationships of the hierarchy: tracking jitter or errors won't cause a hand to detach from an arm, or the car door to twist out of the plane of its hinge. Those would be physically impossible, and GeoH tracking won't let it happen.

Those geometric constraints can help tracking as well: tracking interrelated parts can produce more data than tracking either part individually would, or allow less data to be used than would otherwise be required. GeoH tracking helps you take better advantage of what you know.

The scene can be exported, including individual object and mesh paths, positions and joint angles between the parts of the hierarchy, and deformed meshes, typically as point cache files. The exports can take the form of motion-capture BVH files, Filmbox FBX files, Alembic ABC files, or application-specific exports such as Blender.

We think you'll find the GeoH tracker to be enormously powerful and flexible, and let you do amazing things! Check out the tutorials below and the new Geometric Hierarchy Tracking manual in SynthEyes (see the Help menu).

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