[X3D-Public] X3D player support for NURBS

[Don Brutzman]

The CAD group has been working for a while to improve example scenes and 
usage of NURBS.  We see this as a part of preparations for defining a 
new X3D CAD Mobile/Interactive Profile.  Here is a status report, 
comments and improvements are welcome.

Currently, the state of support by X3D players for the NURBS component 
is adequate for testing but not yet "ready for prime time."  Some 
players have a few nodes, other players have a lot.  We will need to 
improve if we want to create a broad capability for CAD export and 3D 
printing.

Example scenes and screenshot images for current tests are online.

	http://www.web3d.org/x3d/content/examples/Basic/NURBS/
	http://www.web3d.org/x3d/content/examples/Basic/NURBS/images

Tested players include BS Contact (partial), H3DViewer (partial), 
Instant Reality (good), View3dScene (partial) and Xj3D (good).
Attached is a corresponding visual directory of supporting player 
snapshots. A missing image means that a player didn't render a given scene.

No players showed full support for all aspects of X3D NURBS, so a bit 
more work remains.  We are tracking this progress on our wiki page.

	http://web3d.org/wiki/index.php/X3D_NURBS

Vince Marchetti has detailed explanations of trimming and browser 
differences online, plus a prior browser comparison (still pretty 
accurate list of bugs) from last October.  Not much motion seen by the 
codebase builders though.  Online at

	http://www.kshell.com/pages/trimmed_nurbs_demo
	http://www.kshell.com/pages/nurbs_surface_demo
	http://www.web3d.org/wiki/images/1/17/X3D_Browser_NURBS_Evaluation.pdf

Another minor but common warning:
	<meta name=' warning ' content=' missing default values for knot and 
weight array fields in NurbsPatchSurface (weight default: all 1 values) 
; not required by X3D specification, but some browsers may fail without 
them. '/>

Of note is that several implementations are open source, including 
Java-based prototypes in the examples directory.  So we ought to be able 
to get good compatibility across the board, if implementers can work on 
their codebases.

Currently we have deferred plans to try implementing NURBS in X3DOM due 
to apparent lack of low-level library support.  This remains a worthy 
future topic.

On the authoring side, we are adding rules to X3D Schematron to detect 
problems in NURBS node definitions in example scenes.  I further fixed 
one problem with handling of control point values in X3D-Edit support 
for NURBS, but more testing is needed.  Am also working with Vince to 
see if jGeom might be upgraded and integrated provide further support.

	https://savage.nps.edu/X3dValidator
	https://savage.nps.edu/X3D-Edit

	https://sourceforge.net/projects/jgeom

Authors are welcome to submit other good X3D example scenes, and post 
when they find a good authoring tools for NURBS export.  I've heard good 
things about white dune, but am not experienced with it though.

CAD group participants have been meeting (off and on) Thursday 
afternoons, 2 pacific / 5 eastern to discuss X3D CAD and NURBS on the 
Web3D teleconference line.  Participation welcome.

all the best, Don
-- 
Don Brutzman  Naval Postgraduate School, Code USW/Br       brutzman at nps.edu
Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA   +1.831.656.2149
X3D graphics, virtual worlds, navy robotics http://faculty.nps.edu/brutzman
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