NURBS Editing Support

BRL-CAD has recently implemented support for raytracing of NURBS surfaces, but beyond basic operations such as rotation and translation it has no ability to edit them. This project would implement support for editing NURBS curves and surfaces in the new Archer modeling interface.

Note that editing NURBS in Archer should not assume OpenGL surface representations of NURBS are available. Editing should be possible using wireframe representations of key features, and be mappable to more sophisticated OpenGL based visualization once it appears.

Main tasks would be:

1. Identifying key editing operations (see next) and mapping those operations to openNURBS calls (or identifying that the equivalent routine doesn't exist in openNURBS and will need to be implemented)
2. Implementing librt/libbrep/libged logic to allow those calls to be made
3. Implementing appropriate graphical controls and interface logic in Archer (other primitive editing support code in Archer will provide relevant examples).

NURBS curve editing operations:

• Attach (two splines)
• Detach (end point)
• Connect (splice new curve)
• Trim (cut curve)
• Knot Insert
• Reverse (change direction)

NURBS curve to surface operations:

• Projection (see here)
• Loft/Birail (surface created between curves)
• Cap (surface from closed curve)
• Extrude
• Revolve

NURBS surface editing operations:

• Rebuild/Simplify (remove unnecessary control points)
• Trim (evaluate to untrimmed)
• Bevel/Fillet (replace edge with surface+edges)

References

• http://ayam.sourceforge.net/
  • The Ayam editor is a BSD licensed, Tcl/Tk based modeler for NURBS. It's primary purpose is to serve as a modeler for the RenderMan interface, but at least some of the functionality it implements is of interest to BRL-CAD. It's primary license is compatible with BRL-CAD's, but Ayam makes use of many third party components so be sure to check individual files for license information.

• src/librt/primitives/brep/brep.cpp
• src/libbrep
• src/other/openNURBS
• src/libtclcad

Requirements

• Familiarity with C and C++
• Familiarity with Tcl/Tk
• Basic understanding of NURBS
• (optional) openNURBS and/or Ayam experience