[Korea-chapter] [X3D] CAD Working Group meeting (17:00 PST, February 8th) - Minutes
brutzman at nps.edu
Wed Feb 8 19:38:13 PST 2012
Attendees: Hyokwang Lee, Myeong Won Lee, Vince Marchetti, Don Brutzman.
Regrets: Dick Puk (working with Medical group at DICOM meeting San Diego)
We hope that our French colleagues are following the discussion
with interest. If you would like a special meeting with either
Hyo or myself, please let us know.
We first discussed Macro Parametric Approach (MPA). Professor
Soonhung Han of KAIST was originally thinking that MPA might be
a candidate for a standard, but no longer thinks it would be a
separate standard. We will continue looking at MPA closely
as part of our X3D efforts, and once the entire workflow for
CAD to X3D is clear, then we will decide whether it is appropriate
to consider MPA as part of the X3D standard.
On 2/8/2012 2:39 PM, Hyokwang Lee wrote:
> - B-REPs
> * Comparing MPA/STEP/B-REPs & NURBS
Hyo published some excellent new slides which we examined and discussed.
> I made a diagram to share some idea with you and MPA mesh team.
> It’s a kind of one page strategy diagram. :)
> You can get the original PPT.
- the "Neutral XML" file contains MPA representations
- it is prepared from CSG history list in a CAD file
- The CSG features can vary among different CAD formats
- There is not a strict standard for CSG that all CAD formats
follow, but they do tend to be similar
- ISO STEP includes CSG definitions, but it is not uniformaly
followed by all of the formats
- CSG tends to be the innovative advantage among individual CAD tools,
and it may take perhaps several years for ISO STEP to catch up
and define new constructs
- Going from any given CAD CSG representation to an MPA Neutral XML file
usually requires a translator specific to that CAD format
- Usually these translators are part of TransCad (see slide 2)
- TransCAD is a KAIST tool that includes some commercial internal components
The flow charts in slides 3, 4 are especially interesting.
- dotted lines mean a possible path that is being considered
Wondering if conversion from Neutral MPA XML possible to NURBS? is so,
- that might unify our workflow
- it would keep X3D file output sizes small,
- it would provide good resolution at any scale, instead of
tesslation for a given scale..
- we might find that mapping CSG shapes to NURBS representations is actually
similar to mapping B-REP shapes to NURBS representations, at least
for primitives. This probably would not work for geometric operations
of subtraction however, but might work for addition or simple shapes.
- As Vince said, the CSG operations are the "bread and butter" of CAD engines,
so maybe this approach isn't really sensible. It is included here for
discussion. Even if NURBS can only be used for a small percentage of
MPA conversions, they do have advantages over tesselated meshes.
- X3D NURBS do not have to be tesselated, they can remain as NURBS for rendering
One conclusion from slide 3 could be that, given a CAD file with a mix of
CSG and B-REP information, the resulting X3D file would contain meshes and
NURBS, and not need anything else.
We worked hard on Hyo's diagrams, and split diagram 3 into 2 parts:
Candidate Work Flows and Probable Work Flows. The second one is
very appealing because it looks a simple unified workflow is achievable
using what we know today.
See attached refined slides, especially #4 please.
> * B-REPs rendering based on NURBS component
This topic was discussed in detail during the previous meeting.
Everything still makes a lot of sense, please read Vince's paper.
He will add it to the CAD group wiki under Resources.
> - Creating Examples
The current examples are very limited.
We discussed the continuing need for good simple examples.
> * Instant Reality Problems with NURBS
This problem is still pending, Vince wrote a detailed analysis
previously. We need Fraunhofer to engage, who is POC please?
We will review the NURBS examples at next months meeting.
Vince will send some to add to the archive. The CAD group
has taken responsibility for reviewing NURBS implementations
since they are so important for CAD conversion.
> * NURBS code disabled in the Xj3D branch maintained by NPS
Still no work on that. Did demonstrate that new Netbeans 7.1
works in debug mode with NPS Xj3D, so that will help when we
> - CAD Wiki
We made some improvements today.
Adding one or more diagrams might be more helpful than text.
Good discussion today!
We still need a CAD logo for X3D! Who wants to be famous? 8)
> * Issues in a diagram
Hyo is also considering some further diagrams. Go Hyo Go!! 8)
Lots discussed in detail and documented here... further discussion
is of course welcome, this is how our group progressed so far.
> * active items page
We have lots of action items, it is great to keep working together!
Additional topic: Vince sent separate mail about StepNC Numerically
Controlled used for computer-controlled machining, drilling, milling
Subject line is "Comments on the CAD implementation discussions"
We decided to meet again as planned next month, as usual the
second Wednesday is March 14.
Long meeting again... 2 1/2 hours! but very productive, and
probably a lot better than 2 meetings! Many thanks everyone.
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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