Filip,
There are three NURBS tessellation methods currently implemented in the code. One is an
old one that does piecewise subdivision into Bezier patches, and then naively tessellates
each patch to a specified mesh density. It usually results in a highly detailed mesh
that you'd probably want to then decimate (and it was rather slow). The main problem
with that method is that it is hooked into BRL-CAD's "old" / previous boundary
representation support ('bspline' entities), which suck for other reasons and aren't what
the step-g importer creates.
The step-g importer creates "new" NURBS boundary representation objects ('brep'
entities), and has two basic tessellation methods. One just does a quick iteration over surfaces
and gest a quick set of triangles -- this is what yo usee if you draw shaded in Archer (or
"draw -m1 object" in mged). It's intended for visualization.
The other method is stubbed in a compile-time WATER_TIGHT preprocessor block that hasn't
been released yet. As the name suggests, this method goes a bit further to "seal
the gaps" between two adjoining surfaces while it tessellates. It was implemented
somewhat quickly and without a lot of testing, which is why isn't not exposed yet to
userland anywhere. That's where I'd start, though ( src/librt/primitives/brep/brep.cpp).
If you're interested in the code, the function that currently tessellates when
you draw is the *_plot() callback, but for g-stl what is needed is the *_tess()
callback.
Cheers!
Sean
On Jul 26, 2017, at 11:18 AM, Filip Binkiewicz <fi...@3dhubs.com> wrote:
Hey, Robert,
I very much appreciate your effort to help me. I have tried using FreeCAD for
this purpose.
It is, however, dependent on OCC, which runs an algorithm that is not
satisfactory for my
application (as you can see on the example - the tessellation is far from
smooth, and
when you increase the tessellation precision, the file gets unacceptably large,
compared
to commercial software, like Autodesk Fusion 360).
This is why I tried BRL-CAD, which is even more mature than OCC. I may be able
to add a patch for BRL-CAD for tessellating NURBSs, but I will have to do more
research before that
Thank you for your help,
Filip
On Wed, Jul 26, 2017 at 5:00 PM, Bob Anderson <bob.ander...@survice.com> wrote:
Here is an example of the Python script to automate this from FreeCAD’s website
(https://forum.freecadweb.org/viewtopic.php?t=13833) …
from PySide import QtCore
import Part, Mesh
d=QtCore.QDir("Directory_to_step_files")
d.setNameFilters(["*.step", "*.stp"])
files = d.entryInfoList()
for i in files:
shape = Part.Shape()
shape.read(i.absoluteFilePath())
mesh = Mesh.Mesh()
mesh.addFacets(shape.tessellate(0.01))
mesh.write(i.absolutePath()+"/"+i.baseName()+".stl"
Robert Anderson
From: Filip Binkiewicz [mailto:fi...@3dhubs.com]
Sent: Wednesday, July 26, 2017 9:32 AM
To: BRL-CAD Users Mailing List <brlcad-users@lists.sourceforge.net>
Subject: Re: [brlcad-users] Hey, I'm trying to convert a STEP file into an STL
triangle mesh, and BRL-CAD seems to be the perfect match for this task. I am
having trouble achieving it, however. Here's what I do I take any model, let's
say this one: https://raw....
Hello, Sean,
thanks for the news. When can I expect support for NURBS tesselation?
Also, you mentioned that this isn't yet exposed - does this mean it is
implemented?
Is there a way to expose it in my local fork and if there is, where should I
start looking?
Cheers,
Filip
On Wed, Jul 26, 2017 at 3:00 PM, Christopher Sean Morrison <brl...@mac.com>
wrote:
Hi Filip,
You’re not doing anything wrong. You ran into an unimplemented feature.
Now, when I try to produce an STL file, I get an error:
$ ./BRL-CAD_7.26.0_Linux_x86_64/bin/g-stl -o aube_pleine.stl aube_pleine.g
Assembly1
ERROR(Brep_2.s): tessellation failure
0 triangles written
I don't know how to handle this, as I am quite new to BRL-CAD - I would
appreciate some insight
When you imported the STEP file, it contained a NURBS boundary representation
(brep) entity. Support for converting NURBS into triangles (i.e.,
tessellation) isn’t yet exposed as a feature, so the export reports a failure.
There is code that turns the NURBS into triangles for display, but I don’t
think there’s a way to get at those triangles just yet as a user. To any devs
interested in implementing this, look near the WATER_TIGHT define in
src/librt/primitives/brep/brep.cpp. Sorry I don’t have better news Filip.
Cheers!
Sean
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S filipbinkiewicz
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designers to learn about 3D printing.
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