selecting specific brep faces

I have a number of breps made from extruding a surface, which are then trimmed by a surrounding boundary. While all of my breps are of similar basic shapes, trimming them sometimes creates two end faces, sometimes more. I'm basically triying to select only the end faces, whatever their number, and not the main body of the brep.

This is an example of a couple of breps I'm looking at:

although at any given time, there are 18 total. Their orientation is always horizontal on the world plane, but other than that, it varies.

I'm trying to create an offset face like the one at right on all the faces trimmed by the outer boundary, selecting only the end faces is proving difficult.

This is the section of the definition most relevant. The extrusion on the left is the outer boundary that trims the breps, the two brep params are the extruded breps. in this one, I tried isolating each of the breps, using 'brep components', then isolating the face I don't want using 'list item', but the index for this particular face changes depending on the brep.

I feel like there should be a way to get the correct faces from the intersection between the breps and the trimming boundary, but so far no luck. I would greatly appreciate any help. Thank you!

Replies to This Discussion

Permalink Reply by Lauren Richards on August 3, 2011 at 3:28pm

also, this seems to almost work, but there are still some gaps in the surfaces created, and I'm not sure why:

Permalink Reply by Benjamin Golder on August 3, 2011 at 4:26pm

Lauren, can you separate out the portion of the definition that is giving you trouble and post it? I'm having a hard time understanding what you've done already.

One possibility is to measure the angles of the normal vectors of the surfaces, comparing them with normal vectors on the trimming surface. By measuring the normal direction of a surface, you can determine the direction in which it faces.

Another possible means of filtering the surfaces is by surface area. Perhaps you cut sides will be consistently smaller than other sides?

Permalink Reply by Lauren Richards on August 3, 2011 at 5:53pm

It's a little difficult to isolate the section of the definition I'm working on since it draws from so much of what I've already done. I'll try your surface area idea and see if it works out

Permalink Reply by Lauren Richards on August 4, 2011 at 12:02pm

Hi Ben,

The area testing seems to work perfectly, thank you so much!

Permalink Reply by Andrew Heumann on August 3, 2011 at 8:12pm

I can't tell exactly from your pictures, but is it true that the faces that you're interested in are planar, and the rest are not? If this is the case, they should be easy to select by testing for planarity.

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