Something About Offset Surface

Hey, guys, I was recently working on a building facade with undulating balcony railings, somehow, I run into this problem, I lofted two sets of curves into surfaces(or Brep as grasshopper recognized them) , and then the component "Offset Surface" won't work with these surfaces, because, (pic1) according to GH, "Data conversion failed from Brep to Surface".

However, if I bake these Breps into Rhino, I can perfectly use this command, and get my intended result as i like. （pic2）

So, did you guys met this problem b4? Any solution for it? Would be nice to get some hints from u. THX!

Attachments:

20130315180028.png, 197 KB
20130315181554.png, 224 KB

Replies to This Discussion

Permalink Reply by Hannes Löschke on March 15, 2013 at 12:17pm

The OffsetSrf needs a single Surface as input. Often curves contain segments or are split into segments while lofting. Even for single continuous curve this may result in a loft consisting of several surfaces jointed to one (BRep).

You might be able to explode the BReps into surfaces and offset each. Depending on the original surfaces, you can join the offset surfaces back into one.

The command will try to do this behind the scenes if you provide a BRep. Like if you offset a cube in Rhino, you need to specify how Rhino will join the edges of the offset. The GH component doesn't offer this option.

Permalink Reply by Archviator on March 17, 2013 at 10:22pm

Hi thx 4 ur reply, Hannes, I did what u said, explode the BRep, yes, u r totally right, the surfaces now can be offset, however now they would intersect each other, the next thing will be stitch them together, but how to do that accurately, and hopefully the result would be the same as the one I manually created in Rhino? could u elaborate more? Thx!

Permalink Reply by David Stasiuk on March 18, 2013 at 12:40am

You may want to try a different method for generating your base surface to avoid having to explode it at all. You won't have any offset issue if you can keep it a continuous nurbs surface...your best bet for doing this may be to try use the sweep 2 component rather than the loft.

Alternatively, it appears that your surface is basically an extrusion in the z direction with a special trim for the top profile...you could build a trimmed surface simply by extruding your base curve and cutting off the top with your upper profile curve. This surface would also offset cleanly.

Permalink Reply by Archviator on March 18, 2013 at 3:30am

Yeah, thx for the advice, I will try out ur idea as well. Currently, my solution was simply offset the curves first, and then loft them pair by pair, thus creating 4 surfaces, and then joining them, forming such a solid. Although I am not completely sure the result will be identical to the "offset solution", but they look pretty close.

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