RE: Projective Geometry in a CAD Program

From: Charles Overy (
Date: Wed Apr 09 2003 - 20:54:48 EEST


Sounds like you are looking for a 3D architectural CAD program that actually
works the way architects do? None of those.

Seriously though, one of the things that you may have to define first is if
you intent is to create RP, or is it to draw in 3d in the manner that you
would like and then deal with the possible prototypablity latter. I think
this will influence your choices.

We do some of what you describe routinely in FormZ although it is not
usually simple to set up. We have also received autocad files that are set
up the way you describe. Again, it appears not to be trivial and, if you are
going out of autocad to RP you are pretty stuck as you will need a 3rd party
plug in to get more than one solid object out at a time as .stl(at least in
2000, architectural). In both of these programs you will also need to draw
your building using solids if you intend to RP. On the Rhino front, we have
one person in our shop who prefers Rhino most of the time but he
occasionally misses the flexibility to point edit forms that Form Z
provides. As far as the derivation of 2D, I can oly speak for Form Z, where
it is easy, you just render as a hidden line drawing. There was also a post
to the list recently about a tool that was specifically directed at
generating 2D working drawings from .stl. I cannot recall what it is but
someone else might.

On the non solid, simple side, a great many people are having sucess with
Sketch Up. This is a quick architectural sketching modeler. It does do
imports but I have not seen it used in the projection manner you describe.
Also it is a planar modeler, no solids. However, we have sucessfully
resurfaced sketchup data with our new polygonmesh resurfacer and can create
buildable stl files from this data.

Revit is the on again off again hot new architectural modeler. I have used
it a bit but when the got purchased by Autodesk they cut our development
license off. We had a good relationship with them prior. Again no RP output,
you would have to go out through 3DS or DWG/DXF and at last release the
polygon mesh was highly degenerative. Basically, like ACad they are not too
interested in interoperability. They can do most of what you say but again,
it is not a sketch tool, it is a full parametric CAD modeler

Off all of your requirements the section is one of the more ineresting. You
can do this in Form Z but it is not easy. As far as I know you have to cut a
section with a plane or object through each and or all 3d objects. I would
imagine you are looking for a section "slider" interface, x,y,z etc., like
the ones that are very prevalent in RP preprocessing middleware. I have not
seen this useful interface in any architectural CAD but I have not looked
for it extensively. Revit will allow you to position and then operate on a
section view through the 3D model so it is closest that I know of.

We are actively evaluating Nemetscheck's Vectorworks Architect but are not
very far along yet.

Please let me know the results of your search and if you find other resouces
in you investigation. If Makai Smith and Kevin Rotheroe do not respond on or
off the list you may want to ask them their thoughts directly as they are
gurus of Architecture. Also I am working on a CAD/technology in
architecture resources like Jerry Laiserin's . I
appreciate any links.

Very Best,



-----Original Message-----
From: []On Behalf Of
Jonathan Chertok
Sent: Tuesday, April 08, 2003 6:23 PM
Subject: Projective Geometry in a CAD Program

  A. Does anyone know of a CAD program within which one can conveniently do
"projective geometry".

  I am hoping for a 3D program within which I can set up a couple of
"planes" in order to project lines to create a 3D object from a series of
elevations - or to create a series of elevations from a 3D object. I suppose
an ability to snap to a plane and to create a perpendicular to this line
would be useful.

  B. Similarly, I am wondering if there is a program within which one might
have a command "Project Outline" or "Find Points in this Section" which
would yield information in the form of points or lines from which I could
construct additional drawings.

  Here I am hoping for a 3D program which would allow me to construct a 3D
shape - take sections or elevations of it - and then construct additional
drawings using this "section" or "outline" information.

  I have tried this in ACAD 2000 but after a lot of noodling around it
seemed rather unsatisfactory for my needs.


  Jonathan Chertok


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