<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<br>
<font color="#333300"><font size="3"><font face="Times New Roman">All,<br>
<br>
Here is the paper that raised questions about the ability of
traditional CAD systems to model very large structures for
applications such as additive manufacturing.<br>
<br>
This does not mean that they cannot be used for such modeling
but it does imply that new infrastructure is required to
enable such modeling and in my opinion the best hope for a
near term solution is Part 21 Edition 3 combined with AP242,
and the STEP-NC models for additive and subtractive machining.
<br>
<br>
Key advantages include:<br>
1. Interfaces to read and write the geometry to and from
nearly all the CAD systems<br>
2. Very efficient format for modeling facets<br>
3. Information models both additive and subtractive
manufacturing<br>
4. International Standard<br>
<br>
What we need to do is create an infrastructure for processing
this data in very large volumes so that we can support
applications like additive manufacturing, 3D circuit design,
very large buildings construction and very large defense
platforms.<br>
<br>
I would see this mostly as imposing an organization onto the
division of an AP242 file into billions of linked P21 e3
segments.</font></font></font> Seemingly trivial until you
start to think about all the different ways that applications will
want to find and access the data.<br>
<br>
Here is the problem statement that I received from a well known
CAD/CAM vendor<br>
<div class="moz-forward-container"><font face="Cambria" size="2"><span
style="font-size:11pt;">
<div><font color="#BC0082" face="Times New Roman" size="3"><span
style="font-size:12pt;"> </span></font></div>
<div><font color="#BC0082">(1) Simple calculations. Suppose
you have an object with a volume of 1 cubic meter, and the</font></div>
<div><font color="#BC0082">cells in the lattice have a volume
of 1 cubic millimeter. Then there will be 10^9 cells.</font></div>
<div><font color="#BC0082">If you use a curvy b-rep, there
might only be 2 or 3 faces per cell; with a facetted
b-rep,</font></div>
<div><font color="#BC0082">maybe 10 or 20 facets per cell.
But, either way, that’s a huge number of faces. If the
cells are</font></div>
<div><font color="#BC0082">all identical, you can represent
them using a repeated pattern technique some of the time,</font></div>
<div><font color="#BC0082">but, for some operations, you will
actually need explicit representations of all those faces.</font></div>
<div><font color="#BC0082">No modeler (as far as I know) can
handle that many faces, and no graphics card can handle</font></div>
<div><font color="#BC0082">10^9 triangles. Not even close.</font></div>
<div><font color="#BC0082" face="Times New Roman" size="3"><span
style="font-size:12pt;"> </span></font></div>
<div><font color="#BC0082">(2) These folks ... (in the
attached paper)<br>
</font></div>
<div><font color="#BC0082"> </font></div>
<div><font color="#BC0082"> </font></div>
<div><font color="#BC0082">found that ACIS ground to a halt
when they tried to model a lattice with</font></div>
<div><font color="#BC0082">around 2400 simple cells (see pages
9-10). This was 10 years ago, and computers are</font></div>
<div><font color="#BC0082">bigger/faster nowadays, but I don’t
see that this will allow us to make the leap from</font></div>
<div><font color="#BC0082">2400 cells to 10^9. I’d love to be
proven wrong. If plain old b-reps could be made to</font></div>
<div><font color="#BC0082">work, that would certainly make
life easier for us.</font></div>
<div><font color="#BC0082" face="Times New Roman" size="3"><span
style="font-size:12pt;"> </span></font></div>
<div><font color="#BC0082" face="Times New Roman" size="3"><span
style="font-size:12pt;"><font color="#003333">Martin
Hardwick<br>
President STEP Tools, Inc.<br>
Professor of Computer Science, RPI<br>
Team Leader ISO STEP-Manufacturing<br>
</font></span></font></div>
</span></font><br>
</div>
</body>
</html>