Geometry Types

polymesh

Polygonal mesh geometry. A polygonal mesh is formed of points, a vertex list (defining vertices) and start index list (defining faces). Additional information, such as normals and arbitrary data, can also be defined.

Attribute Description
float[3n] geometry.point.N List of per-point normals.
float[3n] geometry.point.P List of points. The geometry points are unique floating point positions in object space coordinates (x, y, z). Each point is only stored once but it may be indexed many times by a particular vertex.
int[] geometry.poly.startIndex

A list of indices defining the faces of a mesh. For example, consider a cube. A cube has a startIndex list size equal to the number of faces in the mesh plus one. This is because we must store the index of the first point on the first face as well as the end point of all the faces (including the first). So, for example, the beginning of a cube’s startIndex list may look like:

  • 0 - 0
  • 1 - 4
  • 2 - 8

The indices for each polygon N are from startIndex(N) to startIndex(N+1)-1. The value at index 0 of the list tells us the first face should start at index 0 in the vertexList, the second value in the list tells us the first face ends at index 3 (n-1).
int[] geometry.poly.vertexList Describes the vertex data of a mesh. There is a vertex at each edge intersection. The value of the vertexList is used as an index into the geometry.point.P list, which stores the actual object coordinates of each unique point. Many indices in a vertexList can index the same point in the geometry.point.P list. This saves space as a vertex is described as a simple integer rather then the three floating point values required to describe a 3D geometry point (x, y, z).
float[3n] geometry.vertex.N List of per-face vertex normals.
float[2n] geometry.vertex.UV List of texture coordinates (per vertex, non face-varying)

subdmesh

Sub-division surfaces geometry. Sub-division surfaces (Subds) are similarly structured to polygonal meshes.

Note

This section is under construction.

Attribute Description
int geometry.facevaryinginterpolateboundary int geometry.facevaryingpropagatecorners int geometry.interpolateBoundary  
int[] geometry.creaseIndices  
int[] geometry.creaseLengths  
float[] geometry.creaseSharpness int[] geometry.creaseSharpnessLengths  
int[] geometry.cornerIndices  
float[] geometry.cornerSharpness  
int[] geometry.holePolyIndices  
float[] geometry.point.Pref  
group geometry.point See polymesh.
group geometry.poly See polymesh.
group geometry.vertex See polymesh.

pointcloud

Point cloud geometry. A point cloud is the simplest form of geometry and only requires point data to be specified.

Attribute Description
group geometry.point See polymesh.

nurbspatch

NURBS patch geometry. NURBS patches are a special type of geometry, quite different from conventional mesh types. A NURBS curve is defined by its order, a set of weighted control points and a knot vector.

Attribute Description
int geometry.uSize int geometry.vSize The size.
float[4n] geometry.point.Pw List of control points and their weights, in the order: x y z w.
int geometry.u.order int geometry.v.order The order.
float geometry.u.min float geometry.u.max Parameters defining the NURBS patch.
float[] geometry.u.knots float[] geometry.v.knots Knot vector, a sequence of parameter values.
group geometry.trimcurves Parameters defining the NURBS patch.

curves

For creating groups of curves parented to the same transform. Curves cannot be created by the UI but can be created through the Python API.

The following XML is from a scene graph that creates 3 linear curves with 3 segments:

<attr type="GroupAttr" inheritChildren="false">
  <attr type="IntAttr" name="degree" tupleSize="1">
    <sample value="1 " size="1" time="0"/>
  </attr>
  <attr type="FloatAttr" name="knots" tupleSize="1">
    <sample value="0.0 " size="1" time="0"/>
  </attr>
  <attr type="IntAttr" name="numVertices" tupleSize="1">
    <sample value="4 4 4 " size="3" time="0"/>
  </attr>
  <attr type="GroupAttr" name="point" inheritChildren="false">
    <attr type="FloatAttr" name="P" tupleSize="3">
      <sample value="0.2 0 5 -2.8 0 2.0 0.5 0 1.0 -0.3 0 -1.5 1.8 0
                     4.9 -0.4 0 2.2 2.5 0 1.0 1.6 0 -1.4 3.8 0 4.9
                     1.6 0 2.2 4.5 0 1.0 3.6 0 -1.4"
                     size="36" time="0"/>
    </attr>
  </attr>
</attr>
Attribute Description
int geometry.basis

An integer indicating the curve basis. This is defined as follows:

  • 0 - No basis
  • 1 - Bezier
  • 2 - B-Spline
  • 3 - Catmull-Rom
  • 4 - Hermite
  • 5 - Power

This follows the BasisType enumeration in the Alembic library.
float geometry.constantWidth A float that defines the width of a curve, which is applied uniformly to each control point.
int geometry.degree Specifies whether curves are linear (degree = 1) or cubic (degree = 3).
float[] geometry.knots

Knot vector is a sequence of parameter values.

Note

When splitting geometry.point.P into multiple curves using knots, the values in numVertices must correspond. For example, given 8 control points in geometry.point.P, degree = 3, and knots = [ 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 ], then numVertices = [ 4 4 ].
int geometry.vstep Sets the vertex stride for the curve. This is used by Katana to calculate the expected length of point-scoped arbitrary attribute arrays.
int[] geometry.numVertices

The number of vertices in each curve.

The numVertices list defines the index ranges of the knots used by each curve.
float[3n] geometry.point.P List of points. The geometry points are unique floating point positions in object space coordinates (x, y, z). Each point is only stored once but it may be indexed many times by the same knot.
float[3n] geometry.point.orientation List of orientations for each control point in the curve, relative to the camera.
float[n] geometry.point.width

List of widths (diameters) of the curve at each control point.

Note

If both geometry.constantWidth and geometry.point.width are set, the values in geometry.point.width are used.

locator

Used only in the Viewer; ignored by the renderers.

Attribute Description
group geometry.point See polymesh.
group geometry.poly See polymesh.

sphere

Built-in primitive type for a sphere, supported by some renderers.

Attribute Description
double geometry.radius The radius of the sphere.

spheres

A more efficient way of creating a group of spheres in PRMan at once. This is ignored by other renderers.

Attribute Description
float[3n] geometry.point.P List of points that represent the sphere centers.
float[n] geometry.point.radius The spheres’ radii.
float geometry.constantRadius Can be used instead of geometry.point.radius to specify a single radius for all spheres.