X3D v4.0 CAD Improvements

These are proposed changes for a future X3D v3.4 Specification under consideration by the X3D CAD Working Group.

X3D CAD Component

• Existing specification: X3D v3.3 CAD Geometry Component

Child-node relationships more explicit

• Many parent-child node relationships are vague, leading to difficulty deciding which children are allowed. For example, X3DGroupingNode is implemented by many candidate nodes.
• These relationships are strictly captured in the X3D DTD and X3D Schema, with further support in X3D Schematron
• In order to best support model export and interoperability, the child nodes are limited to those listed in the CADInterchange Profile

Proposed specification prose: needed.

Tesselation consistency

• Exporters can significantly reduce file size using primitive-geometry nodes (e.g. Cylinder, Disk2D, etc.)
• Tesselation quality is not strictly defined in X3D
• In order to match polygonal tessellation strictly and avoid "cracks" between adjactent geometry, some form of association is needed (similar to the NURBSet node)
• CADPart semantics can be improved to include this constraint

Proposed specification prose: needed.

X3D CADInterchange Profile

• Existing specification: X3D v3.3 CADInterchange profile
• Primary discussion: revising CADInterchange profile email thread

Improved nodeset

Nodes to add:

• Anchor
  • Needed for description and Viewpoint selection (level 1)
  • Also needed for linking to other networked resources (level 2)

• Inline
  • Needed for modular re-use of CAD-model files

Concern: possibility of short-circuiting CAD product structure within an extended file. Related future specification change:

• • Any node children created by Inline, ProtoInstance or Script (via a createX3D method )

need to follow the CAD product structure defined by their parent nodes.

• FillProperties
  • Definitely needed for proper display to distinguish different parts or selected parts. Related to definition of component levels in the profile.

• OrthoViewpoint
  • The primary purpose of OrthoViewpoint is to support common use cases for CAD model viewing. (This node was probably added after the initial CAD profile.)

• ViewpointGroup
  • Allows nesting of Viewpoints within models without exploding or overloading the Viewpoint list, which is an essential tool for user navigation.

Nodes to remove:

Renaming necessary?

Extensive changes to this profile may make backwards compatibility difficult. X3D profiles do not support a concept of level as components do.

• Should the profile be renamed for clarity, maintaining the old profile separately?
• Alternatively should the old profile be deprecated?
• Is there a better way to express this evolution, simply noting that the v3.4 profile is different?