Sections of Solid Brep produce Open Curves

I'm sectioning (similar operation you'd do contours in rhino) a solid brep with some some planes, and they are producing open curves.

I have a feeling that I'm going to have to be more dilligent in creating my solids when modeling in rhino, because I use "join two naked edges" command to adjust the tolerances in order
to get it to read as a solid. Am i right, is that the issue here?

The grasshopper file is a snippet from a very large script, and I am just isolating the error...

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Permalink Reply by Danny Boyes on September 7, 2011 at 3:15am

Hi Will,

There was a very good explanation of this by David recently and I cannot for the life of me find it. Basically it comes down to the fact that tolerance is an issue coupled with the fact that the software does not know what you want to do with the intersection curve next.

However if you did a solid boolean difference on the closed hull with a closed box representing the immersed volume then Grasshopper/Rhino knows to create a closed Brep as a result so any minor gaps will be ignored.

I've attached an example of extracting the upper most face of a Boolean difference representing the WPA

This however is time consuming and will take in the order of 20 seconds to complete just this portion of the Definition.

Another way might be to investigate each set of sectioning results and close them with a line. It gets trickier with multiple segments to a WPA. I would look into this for you but my spare time is soon to be consumed.

Attachments:

SolidIntersectionErrorBoolean.gh, 12 KB

Permalink Reply by David Rutten on September 7, 2011 at 3:37am

You probably meant this.

David Rutten

david@mcneel.com

Leusden, Holland

Permalink Reply by Danny Boyes on September 7, 2011 at 3:40am

That's the one. Thanks

Permalink Reply by Fred Becquelin on September 7, 2011 at 3:59am

Hi,

Yes I've had this kind of problem too. I would not recommend the solid boolean approach since it's very very slow. I do test if the curve is closed ( and planar, since sometimes PlnXBrep output non planar curves (tolerance again) and close with a line. Another way that you can try in some cases is region boolean (with a rectangle in the same plane).

Also, it might be time-saving to use meshes instead of breps.

I have been trying to do this for a very long time... I'm still amazed at Marc Pommelet's MAAT software. Obviously the best of all... Sadly it's far too expensive for me :(( -and for you too I guess...

Check out my video... it's almost in real time.

Cheers

Fred

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