Modeling Paradox

Hello all,

  Now that I've gotten my feet wet with
Radiance, so to speak, I'm left with a bit of
a paradox; Radiance has provisions to describe
almost any conceivable geometry I could need
in modeling buildings; however none of the export
programs I have used take advantage of this-
everything is turned to triangles.

There are times that this simply doesn't work;
such as aiming failures and bad looking curves,
and times where it's merely annoying, in that
I wish to replace some exported geometry from
CAD with Radiance-native geometry, but can't
easily do so because the item I wish to replace
is a tangle of triangles, and it's hard to discern
it's placement from the mess within the RAD files.

I can already produce renderings within
Radiance that are much better than anything
I've done before. However I still haven't
found an efficient and acceptable workflow
due to my reliance on CAD systems for generating
geometry (and their somewhat inferior exporting
ability).

So again I'm bothering all of you in asking
for two things; first off, how much & what do you
typically model in CAD and how much do you typically
describe within Radiance (or array, or instance)
for a given project; and secondly, has anyone
ever made an effort to make a 3D GUI modeler that
uses Radiance as it's native file format?

(would this even be possible?)

Thanks in advance,

Jeffrey

Hi Jeffrey,

  Now that I've gotten my feet wet with
Radiance, so to speak, I'm left with a bit of
a paradox; Radiance has provisions to describe
almost any conceivable geometry I could need
in modeling buildings; however none of the export
programs I have used take advantage of this-
everything is turned to triangles.

What CAD program are you using? What exporter are you using? You have to understand that the basic building block of ACIS-based modeling programs -- when talking to other software -- is the damned triangle, unfortunately. 3DStudio is great at producing models with more curves than Pamela Anderson, but when you ask it to export that model for use in another application, it spews forth a zillion triangles. It's not a Radiance limitation, it's an ACIS translation problem.

There are times that this simply doesn't work;
such as aiming failures and bad looking curves,
and times where it's merely annoying, in that
I wish to replace some exported geometry from
CAD with Radiance-native geometry, but can't
easily do so because the item I wish to replace
is a tangle of triangles, and it's hard to discern
it's placement from the mess within the RAD files.

AutoCAD, when used with Georg Mischler's Radout program (http://www.schorsch.com/download/radout/), can produce much cleaner models. I use AutoCAD and 3D faces as much as possible. When you use 3D solids in AutoCAD, the only way to get them out of ACAD is to convert them to a 3DStudio mesh first, and that means triangles (and oftentimes, LOTS of triangles).

As for the placement of native Radiance geometry, have a look at replmarks (http://radsite.lbl.gov/radiance/man_html/replmarks_1.htm). You can use your CAD program to place (with great accuracy and familiarity) markers that can be easily swapped out with a .rad file or an octree (but don't use octrees for light sources, as I found out the long way [http://www.radiance-online.org/pipermail/radiance-general/2003-August/000946.html]!)

I can already produce renderings within
Radiance that are much better than anything
I've done before. However I still haven't
found an efficient and acceptable workflow
due to my reliance on CAD systems for generating
geometry (and their somewhat inferior exporting
ability).

So again I'm bothering all of you in asking
for two things; first off, how much & what do you
typically model in CAD and how much do you typically
describe within Radiance (or array, or instance)
for a given project; and secondly, has anyone
ever made an effort to make a 3D GUI modeler that
uses Radiance as it's native file format?

You know what? I've been slowly learning Radiance over the last year and a half, and I still don't have a real workflow, and I know that's my biggest problem right now (well, that and the fact that I need to cut down on the cholesterol). Right now I use CAD and try to use 3Dfaces as much as possible, export with radout, and do some replmarks shenanigans for swapping out light sources. Manual arrays with xform are used every once in a while, when the building supports it, but that is rare. I think a lot of us rely on CAD for accuracy, I wouldn't worry about that; people like Greg Ward and Carsten Bauer who use vi to build entire Radiance scenes are in the minority, and are completely insane. =8-) Seriously, there's nothing wrong with relying on CAD for things; CAD is really good for things like building precision models. But I'd love to hear yours and others' methods for making the jump from CAD to Rad.

Rob Guglielmetti
[email protected]
www.rumblestrip.org

Rob Guglielmetti wrote:

What CAD program are you using? What exporter are you using? You have to understand that the basic building block of ACIS-based modeling programs -- when talking to other software -- is the damned triangle, unfortunately. 3DStudio is great at producing models with more curves than Pamela Anderson, but when you ask it to export that model for use in another application, it spews forth a zillion triangles.

Dammit Greg, we want a Pam Anderson primitive in RADIANCE! :^)

···

--
Roland Schregle
PhD candidate, Fraunhofer Institute for Solar Energy Systems
RADIANCE Photon Map page: www.ise.fhg.de/radiance/photon-map

END OF LINE. (MCP)

Hi,

I remember it, I was at this point, too, some years ago in my life. Its one of the oddities of Radiance, having a powerful rendering engine but - at the first glance - no 'convenient' way to set up / put in a model. This is no complaint, consider that the stuff is for free, and you already get a rendering engine more or less surpassing many commercial packages in terms of quality and being currently accepted as the de facto standard for accuracy in terms of lighting analysis.

I once thought about writing some import module for Radiance geometry, but soon made up my mind. It probably is not very difficult, but it needs a lot of time and tedious work, and after all you'll end up reinventing another CAD program, although there are lots of them already on the market.. Additionally, with modern PC equipment and their high amount of RAM, treating geometry as polygon-meshes is not so much a limitation as it has been before (I remember that POV ray uses lots of different primitive types, for the more complex ones you need sophisticated root solvers to determine ray intersections, meaning longer calculation time)

Nevertheless, so far I worked exclusively with an editor and the Radiance native formats (Hi Rob, you're absolutely right, with one exception of course, I'm insane, but I'm not masochistic, so I don't use vi.... :slight_smile: . But even when working with CAD programs, its good to rely on exact coordinate specification rather than on mouse-drawing, to avoid inaccuracies like accidental small gaps between edges resulting in light leaks or other artifacts which need a lot of time to get tracked down later.

Another Tip: decompose your model in separate items as much as possible, and let the Radiance input engine put them together when calling oconv, the simplest means are often the most effective ones.

-cb

Hi Jeffrey,

What CAD program are you using? What exporter are you using?

I am using AutoDesk Revit for the modeling, then exporting
from that to AutoCAD where everything becomes a polyface mesh,
and then using RADOUT to generate my .RAD files. The other
approach I've done is to export from Revit to DXF in parts,
and then use the DXF2RAD tool to translate them into .RAD.

The problem I have, and hence why I have to use AutoCAD
as an intermediary currently, is that AutoDesk Revit doesn't
have the ability to export geometry so that material = layer
within a DXF or DWG; instead it places elements upon layers
based upon those elements classification; i.e. existing walls,
new furniture, site elements, etc. Revit also currently lacks
an API, so I can't write my own Radiance exporter for it.

So, the best way I've found to export from Revit to
Radiance is to first export to a DWG or DXF file, open
that in AutoCAD, swap things onto layers per what
material I want them to be, then use RADOUT to generate
multiple .RAD files.

However the modeling capabilities of Revit *far* outshine
those of AutoCAD when it comes to modeling buildings; so
even having to jump through these translation hoops, it's
still faster than modeling in AutoCAD to begin with. Revit
is, more or less, 'Inventor or SolidEdge for Architects'.

You have
to understand that the basic building block of ACIS-based modeling
programs -- when talking to other software -- is the damned
triangle,
unfortunately.

That's what I've encountered.
  

It's not a
Radiance limitation, it's an ACIS translation problem.

Oh no, I never ment to imply that it was a Radiance
limitation; I meant to imply that it was a limitation
with the translation programs; in that
they aren't aware enough to translate, say, a cylinder
in a DXF to a cylinder in Radiance.

AutoCAD, when used with Georg Mischler's Radout program
(http://www.schorsch.com/download/radout/), can produce much cleaner
models. I use AutoCAD and 3D faces as much as possible.

Another benefit of using AutoCAD as an intermediary
from Revit is what you mention here; indeed using the
RADOUT tool I've had much less issue with aiming failures,
as well as replacing the luminescent parts of my light
fixtures within AutoCAD with simple AutoCAD 3Dface elements
has helped immensely.

When you use
3D solids in AutoCAD, the only way to get them out of ACAD is to
convert them to a 3DStudio mesh first, and that means triangles (and
oftentimes, LOTS of triangles).

I'm not using Soilds anymore; when I export from
Revit, everything comes into AutoCAD as a polyface
mesh.

As for the placement of native Radiance geometry, have a look at
replmarks
(http://radsite.lbl.gov/radiance/man_html/replmarks_1.htm).
You can use your CAD program to place (with great accuracy and
familiarity) markers that can be easily swapped out with a
.rad file or
an octree (but don't use octrees for light sources, as I
found out the
long way
[http://www.radiance-online.org/pipermail/radiance-general/200
3-August/
000946.html]!)

Thanks a great deal for this link. I'm certain that
this will help a great deal! Something like this
was exactly what I was looking for; lacking the
ability to make 'good' RAD files directly from
my CAD software, I needed some way to easily
'swap' elements within my scenes. Thanks again!

Right now I use CAD and try to use
3Dfaces as much as possible, export with radout, and do some
replmarks
shenanigans for swapping out light sources.

This sounds like what I'll do, at least until
Revit has an API!

Thanks again,

Jeffrey

Hi Jeffrey,

Jeffrey McGrew wrote:

I am using AutoDesk Revit for the modeling, then exporting
from that to AutoCAD where everything becomes a polyface mesh,
and then using RADOUT to generate my .RAD files. The other
approach I've done is to export from Revit to DXF in parts,
and then use the DXF2RAD tool to translate them into .RAD.

However the modeling capabilities of Revit *far* outshine
those of AutoCAD when it comes to modeling buildings; so
even having to jump through these translation hoops, it's
still faster than modeling in AutoCAD to begin with. Revit
is, more or less, 'Inventor or SolidEdge for Architects'.

Sounds interesting. I must admit I don't pay close attention to what's coming out of Autodesk's, um, doors, besides AutoCAD. I use my AutoCAD/ADT and hope that they don't raise the price too much. Revit sounds interesting though. Perhaps I'll have a look.

It's not a Radiance limitation, it's an ACIS translation problem.

Oh no, I never ment to imply that it was a Radiance
limitation; I meant to imply that it was a limitation
with the translation programs; in that
they aren't aware enough to translate, say, a cylinder
in a DXF to a cylinder in Radiance.

I never meant to imply that you meant to imply that either. Wait; now I'm confused. =8-) Yes, it's frustrating to accept that while Radiance can deal with fantastic complexity, and smooth curves (don't get me started on *that* again), it does so internally. You either speak Radiance or accept lots of triangles or facets. I guess most of us accept triangles. It's less of a limitation than it was in the past, what with memory & CPU cycles coming cheaply now, but it still makes for illum headaches and I guess texture mapping is a pain.

Thanks a great deal for this link. I'm certain that
this will help a great deal! Something like this
was exactly what I was looking for; lacking the
ability to make 'good' RAD files directly from
my CAD software, I needed some way to easily
'swap' elements within my scenes. Thanks again!

Yep, it's indispensible for that, and I assume is exactly why Greg wrote it. Have fun!

···

----

      Rob Guglielmetti

e. [email protected]
w. www.rumblestrip.org