Draft of the look and feel of a simple pythonic API for CSG

Hey Thomas,

A while ago, you and Jelle were talking about creating an API for
pythonOCC that would simplify and hide the ugly guts of OCC. I haven't
seen too much on this front in a while, but a few days ago I was
talking with Christian Siefkes, Ben Lipkowitz, and a few others about
a potential look and feel for python that would hide away OCC, or even
BRLCAD or anything else that we opt to throw under the hood.

I was wondering if I could get some thoughts on how this feels:

http://designfiles.org/~bryan/csg.py

sphere = Sphere(position=(0, 0, 0), radius="5 mm")
base = Circle(diameter="20 mm", position=(0,0,0))
cylinder = base.extrude(length="10 mm", direction=Vector(0, 0, 1))
sphere.position = (0, 0, 10)
lamp_post = cylinder.fuse(sphere)

#if you're in an X11 opengl session thingy:
display.add(lamp_post)

#or if you want to export it:
iges_data = lamp_post.to_iges()
file_handler = open("lamp_post.iges", "w")
file_handler.write(iges_data)
file_handler.close()

And maybe some parametric PAF stuff?

base = Circle("base of base plate", diameter="20 mm")
base_plate = Extrusion(base, "10mm", Vector(0,0,1))
#OR: base_plate = base.extrude("10 mm", Vector(0, 0, 1))
#OR: base_plate = extrude(base, "10 mm", Vector(0, 0, 1))
base_plate.name = "cylinder 1"

assert base_plate == Cylinder("cylinder 1", diameter="20 mm",
height="10 mm"), "Cylinder and base plate should be exactly the same"

base_plate.diameter = "25 mm"
assert base.diameter == "25 mm", "base diameter should have been updated"

base.diameter = "32 mm"
assert base_plate.diameter == "32 mm", "base plate diameter should
have been updated"

I am not entirely sure how to do this sort of feature tree. Any hints
or advice from interested bystanders would be hawt. Also, I am sending
this over to OpenSCAD because they have a similar thing going on, with
their own parser, but nevertheless would probably be interested in
python hooks and somehow influencing how those hooks feel & work.

Thanks,

- Bryan
http://heybryan.org/
1 512 203 0507

On Sun, Feb 21, 2010 at 1:49 PM, Jelle Feringa wrote:
Have you checked out libged from BRLCAD? There's CSG support going on,
believe it or not.

> When discussing the higher level API ( yes please ;'), please do so in reference to the work-in-progress: /src/addons/KBE/Level2API.py

Granted. Here's a link, then, since I can't seem to find it elsewhere
on the internets:

http://designfiles.org/lab/opencascade/Level2API.py

- Bryan
http://heybryan.org/
1 512 203 0507

On Sun, Feb 21, 2010 at 1:59 PM, Thomas Paviot <[hidden email]> wrote:
> Hi Bryan,

Hey Thomas. Thanks for the quick reply.

> *Very* intersting thread, thank you for opening it.

had to be done

> The topic you're talking about is still an open issue in CAD and
> contributions from the open source community would certainly be a great
> thing. However, it's not only a technical problem (in terms of
> implementation), but rather a scientific one. As far as I know, a good
> starting point is the second edition of the AP203 STEP application protocol,
> especially the ISO10303-55 (‘Procedural and hybrid representation’). Being
> able to implement this part of the standard in a scripting langage would
> already be a huge step.

Yes, absolutely. I do not have access to the ISO documentation on
STEP. Maybe you can send a few files my way to help me out? There is
one other resource that I am aware of- namely, the STEP export API in
the OpenCASCADE source code. From this, it is possible to extract the
valid entities that can be found in a STEP file in the EXPRESS
language. But then you have the issue of adopting OCC's peculiar
standard or peculiar implementation of STEP. Here's a skeleton of STEP
features that I figured out by looking at the OCC source:

http://designfiles.org/~bryan/step_importer.py

> I think this approach would certainly be the easiest way to get started: the
> STEP data model has been widely discussed and validated.

Right now what we need most are the ISO 10303 documents. Otherwise I
suspect nothing will happen. Whether or not this could be used to make
an API is also another issue- I suspect so, but maybe we should forge
ahead even if we can't get the ISO docs?

- Bryan
http://heybryan.org/
1 512 203 0507

---------- Forwarded message ----------
From: Thomas Paviot <[hidden email]>
Date: Sun, Feb 21, 2010 at 2:24 PM
Subject: Re: [Pythonocc-users] Draft of the look and feel of a simple
pythonic API for CSG
To: Bryan Bishop <[hidden email]>


2010/2/21 Bryan Bishop <[hidden email]>
Bryan,
You'll have to buy the CD in order to have documentation. However,
there's a webpage dedicated to AP203ed2 here:
http://www.steptools.com/support/stdev_docs/express/ap203e2/index.html
The EXPRESS data model file can be browsed at:
http://www.steptools.com/support/stdev_docs/express/ap203e2/html/index.html
I learnt most of the STEP standard by reading the EXPRESS files.
Thomas

>
> http://heybryan.org/
> 1 512 203 0507




--
- Bryan
http://heybryan.org/
1 512 203 0507