Geometry types

The following geometry types are supported:

• Polygonal meshes (including subdivision surfaces)

• Spline curves

• Particles

All geometry types support motion blur. If the mesh/hair topology or particle count are not changing, then precise motion blur is computed. Otherwise, velocity channel must be provided in the file to describe the motion blur.

Mesh Objects

• Velocity channel - It is always computed for animations with homogeneous topology. Otherwise, it is read from the standard alembic velocity property in units/second. Alternatively, it is in units/frame in a geometry property specified in "velocity_color_set" GeomMeshFile plugin parameter, or in geometry property named “v”, “velocities”, “velocity”, “Velocity”;

• Material IDs - P rovided by per face uin32 property named “.materialids” or by alembic face sets. Each face set name which start with a non-negative integer will assign this integer as material id. Face set names which do not start with an integer receive consecutive material ids;

• Normals - If “compute_normals” is on, then normals are always computed with the given “smooth_angle” parameter. Otherwise they are read from the alembic default property for normals. If they are not written then geometric normals are used;

• UV channels - All vector2 float/double properties in ArbGeomParams that start with “uv” are sorted and listed as UV sets. The default UV set comes first with name “uv”;

• Color channels - All vector3, color3 and color4 properties are represented as three component color channels. All other scalar geometry properties are packed into three component colors.
  

Hair Objects

• Velocity channel - It is always computed for animations with homogeneous topology. Otherwise, it is read from the standard alembic velocity property in units/second;

• Hair width - Either written as standard alembic property expressed as diameter or written as radius in “.radius” property;

• UV channels - All vector2 float/double properties in ArbGeomParams that start with “uv” are sorted and listed as UV sets. The default UV set comes first with name “uv”. UVs can be per vertex of per strand.
  

Particle Objects

• Velocity channel - It is always computed for animations with homogeneous topology. Otherwise, it is read from the standard alembic velocity property in units/second;

• Particle width - It is either written as standard alembic property expressed as diameter or written as radius in “.radius” property.