[X3D-Public] Fwd: Re: Comments please on Nurbs component

[Don Brutzman]

Vince, thanks for these excellent comments.  Apologies that I didn't
see this earlier.  Here they are on list (with permission) for review.


-------- Original Message --------
Subject: Re: Comments please on Nurbs component
Date: Mon, 20 Feb 2012 21:47:30 -0500
From: Vincent Marchetti <vmarchetti at ameritech.net>
To: Don Brutzman <brutzman at nps.edu>


On Feb 13, 2012, at 7:21 PM, Don Brutzman wrote:

> Vince:  when convenient, please review these v3.3 changes to the NURBS component
> and see if there are any changes or additions you think might be necessary.
> 
> Extensible 3D (X3D), ISO/IEC 19775-1:2008/PDAM1:201x — 27 Nurbs component
> http://www.web3d.org/files/specifications/19775-1/V3.3/Part01/components/nurbs.html
> 
> Baseline: v3.2 specification
> http://www.web3d.org/files/specifications/19775-1/V3.3/Part01/X3D.html
> 
> Thanks for all comments.  We need any comments this month, since there is a
> final X3D v3.3 ISO Specification Editors Meeting on 12 March 2012.  TIA.

Don

I found a few things:

For section 27.2.3:

The penultimate sentence of this last paragraph should also be changed.
Replace:
"Within the knot vector there may not be more than order−1 consecutive knots of equal value"

with:
"The initial \it{order} knots may be equal, and the final \it{order} knots may be equal, otherwise there may not be more than \it{order−1} consecutive knots of equal value."

Explanation: This is the standard requirements on the knots for non-uniform splines, and is the definition used in the NURBS Book given as a reference (Piegl and Tiller, 1997) although it is mathematically redundant. See Example 7.2 from that book; defining a circle with a order=3 (degree=2) NURBS curve; the knot vector is: [0,0,0,0.25,0.25,0.5,0.5,0.75,0.75,1,1,1] -- note the 0 and 1 repeated 3 times.

-----------------------------------

Section 27.3.1

Final sentence: word "descendent" -- replace with "descendant"

On the other hand, this is more matter of usage than a misspelling, see http://www.grammarist.com/usage/descendant-descendent/

-----------------------------------
Section 27.3.2

A paragraph contains a repeated sentence:

Suggest replacing:
"A closed surface shall be specified by repeating the limiting control points and setting the closed field to TRUE. If the closed field is set to FALSE, the implementation shall not be required to smoothly blend the edges of the surface in that dimension into a continuous surface. A closed surface in either the u-dimension or the v-dimension shall be specified by repeating the limiting control points for that dimension and setting the respective uClosed or vClosed field to TRUE. If the last control point is not identical with the first control point, the field is ignored. If either the uClosed or the vClosed field is set to FALSE, the implementation shall not be required to smoothly blend the edges of the surface in that dimension into a continuous surface."

with:
"A closed surface in either the u-dimension or the v-dimension shall be specified by repeating the limiting control points for that dimension and setting the respective uClosed or vClosed field to TRUE. If the last control point is not identical with the first control point, the field is ignored. If either the uClosed or the vClosed field is set to FALSE, the implementation shall not be required to smoothly blend the edges of the surface in that dimension into a continuous surface."

-----------------------------------
Section 27.4.14

The caption for the graphic that appears here should be changed to
"Figure 27.5 -- NurbsTrimmedSurface"




Vincent Marchetti
vmarchetti at ameritech.net



.



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