[cgma-dev] get_graphics for OpenCascade?

[Jane Hu]

Hi, David:

First of all, CGM doesn't support interface for get_graphics for bodies.
However, you can call a loop to get_graphics for each of the surfaces in
the body. Notice also, for surfaces, the max_edge_length variant is not
respected in OCC.

I checked the interface in OCC for triangulation for get_graphics purpose,
it seems that user can request a body as a input.

In general, as Tim mentioned, even if it gives back triangulations for
surfaces, it seems there's no words to guarantee satisfying watertight
and/or confirmal on the boundary: Opencascade.org forum did have a topic on
*Triangulation of thin ring contains gap* (
http://www.opencascade.org/org/forum/thread_23638/?forum=3)

If you need such an interface, I can try to fix one for you, and you'll
have to test out if it's watertight for your model. I'll try to implement
and let you know.

Have a nice one!

Jane


On Thu, Aug 15, 2013 at 9:04 AM, Tim Tautges <tautges at mcs.anl.gov> wrote:

> On the function variant, I'll let Jane answer that.
>
> As for watertight triangulations from the faceter, for single volumes,
> from ACIS, the faceting is generally watertight (though the facets from
> separate surfaces don't share points).  But for multiple volumes sharing
> surfaces, the faceting often won't be watertight.  There's a tool in
> MeshKit that does make facet models coming from CAD watertight, and has
> shown good robustness even for huge models.  There's an incoming bug fix
> due to a regression awhile back that you'll have to wait for, I'll check
> when that's coming (Andy, can you comment?).
>
> - tim
>
>
> On 08/15/2013 08:19 AM, David Thompson wrote:
>
>> Hi all,
>>
>> I'm curious if there's a reason why the variant of
>> GeometryQueryEngine::get_**graphics() that takes a BodySM* instead
>> of a Surface*/Curve* is unimplemented in OpenCascade. I am hoping to get
>> a conformal mesh out for a couple reasons:
>> (1) I'd like to avoid the cracks that appear when individual faces are
>> tessellated independently and (2) a
>> triangle-based modeler I'm working with expects watertight triangulations
>> to maintain its internal state
>> consistently.
>>
>> Is there an underlying deficiency in OpenCascade that has to be addressed
>> before it makes sense to implement the
>> BodySM* variant, or has it just not been needed yet?
>>
>> Thanks, David
>>
>>
> --
> ==============================**==============================**====
> "You will keep in perfect peace him whose mind is
>   steadfast, because he trusts in you."               Isaiah 26:3
>
>              Tim Tautges            Argonne National Laboratory
>          (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
>  phone (gvoice): (608) 354-1459      1500 Engineering Dr.
>             fax: (608) 263-4499      Madison, WI 53706
>
>


-- 
Jane Hu

Asst. Researcher
Dept. of Engineering Physics
UW @ Madison

"And we know that for those who love God, that is, for those who are called
according to his purpose, all things are working together for good."
(Romans 8:28)
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