RE: ACAD NURBS > RHINO and Gen'lly More Robust 3D CAD

From: Makai Smith (
Date: Fri Apr 11 2003 - 17:00:30 EEST

To be really dumb about this, I've noticed that ACAD won't IGES out, but at
least it will ACIS (*.sat) out. This exports NURBS, but ignores the 2d
stuff, like splines. Mech desktop I think has IGES.

Heck, ACAD exports stl, so you *can* get stuff machined without ever using
IGES. I've only used deskproto and surfcam, mickey mouse stuff maybe, but
stl was fine. Actually, I think I went VRML into deskproto!

Architecture trains for ACAD, but its dominance in the marketplace will
wane. Revit is evidence of this fact: autodesk is now selling a
"discontinuous" product. In Phil Bernstien's own words, "no one ever got
into architecture because they liked the autocad interface". When you read
Laiserin you'll find that BIM *will* kill CAD (or rather fulfill its

Anyway, acad is great for drawing drawings, but it is beastly when it comes
to complex 3d. You have to keep reorienting the UCS (formZ is even a bit
annoying that way). Try modeling in 3DS or Maya. When you get a taste of
objects with their own relative coord systems, and a hierarchical database,
you'll never like acad again, IMHO. There's just a brittleness to acad; the
richness and fluidity of a true 3d toolset blows it away. And let's not
even get into parametric modeling.


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-----Original Message-----
From: Jonathan Chertok []
Sent: Thursday, April 10, 2003 5:38 PM
Subject: ACAD NURBS > RHINO and Gen'lly More Robust 3D CAD


1. Can anyone tell me if there is a special way to get NURBS curves from
ACAD 2000 into Rhino. I have some curves modelled in ACAD, but they seem to
come into Rhino without all the through points.

2. Also, can anyone tell me exactly the limitations of ACAD 2000 are
particularly with respect to 3D and NURBS modelling. My reading tells me
that "Autocad is a Non-Uniform Rational B-Spline (NURBS) modeller and uses
polygon meshing to create 3D surfaces" (ACAD 2000 3D - Matthews). This
sounds pretty good for my uses. What exactly would this not allow you to do
with respect to manufacturing (as opposed to rendering)?

3. I have also run across the statement "Unlike Mechanical Desktop you will
find Autocad is limited as a surface modeller." Can anyone give me a
common-sense understanding as to what Mechanical Desktop (or 3D Studio) can
do for me that Autocad cannot?

4. If there is a ACAD NURBS (or overall NURBS) Guru out there I wouldn't
mind picking their brain about a couple other issues as well.

5. And tangentially (I think) can I go from .stl to IGES relatively easy in
order to get some things machined? Or is this a tricky bunch of business? Is

there a date that this was discussed on RPML, name of person who posted the
question, etc?


I'm a monster on ACAD (and hate to put all that "Masonic Knowledge" aside,
but I would like to step up my 3D Modelling capabilities (like getting
points in space from 3D objects and being able to projectively work with
shapes...) as it relates to my architectural - and other - work. Do I go
with 3D Studio, Mechanical Desktop, Rhino, or look in another direction?
Charles has specifically mentioned Revit and Nemetscheck's Vectorworks
Architect - neither of which I am familiar with...has anyone got a handle on

where I can get more information about the state of the state with respect
to more robust 3D CAD Programs. Speaking of which what does Bentley do for

I suppose I can pick and choose programs depending on what I am doing, but
it would be great to get more of a handle on what does what and what is
coming on strong.



P.S. I will be taking a closer look at Jerry Laiserin's site with respect to

these issues and also would appreciate any suggested links.

Universal Joint Design Build
Full Service Design and Construction

Jonathan Chertok. Principal
Austin Texas [512] 407 9628

Buildings + Digital Manufacturing

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