How to unify face normals in a brep with VB?

Hello everyone,

I'm creating a group of faces in a brep, which I then process with the createsolid command.

This works for most of the breps, but a few of them have some faces that are turned the wrong way. Apparently this happens to the way they are drawn on the surface grid that I'm using.

I only discoverd this when I exported the baked breps as OBJ and found in 3dsmax that some of the faces are flipped.

So is there a way to unify all face normals in one brep with a VB command?

Thanks,

Fernando

Replies to This Discussion

Permalink Reply by David Rutten on May 30, 2012 at 8:14am

Hi Fernando,

Rhino should adjust normals itself when two faces meet at an edge. If this isn't happening correctly when it's a bug that needs to be fixed deep in the core. It might also be a problem with the OBJ exporter. When a face normal is flipped, the underlying surface isn't actually modified (The U or V directions would have to be adjusted), but there's a boolean on each BrepFace that indicates flippedness. Unless you know about this boolean, you may well use the implied normals rather than the adjusted ones.

Please bake your brep and post it here as 3dm so I can have a look at it.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Fernando Conti on May 30, 2012 at 8:43am

Hi David,

I think I didn't explain it very well. Some of the solids were created, and with others the createsolid command (I took it from your script here: http://www.grasshopper3d.com/forum/topics/running-a-macro-that-bakes-a ) just left the faces in the brep as they were with the messags 'unable to create solid'.

I have attached a file with the solid and non-solid outputs from the script. The script does the same for each solid, so I don't understand why some succeed and other don't.

Maybe you can discover what is different with the failed ones.

Thanks,

Fernando

Attachments:

createsolids.3dm, 1.3 MB

Permalink Reply by Fernando Conti on June 4, 2012 at 6:02am

Hi David,

If you had the time to look at it, do you think there is a way to fix this?

Thanks,

Fernando

Permalink Reply by David Rutten on June 4, 2012 at 6:57am

Hi Fernando,

the faces in the file you posted are not accurate enough to join them into closed shapes. There's gaping holes along many edges. I don't know if this is just a result from the tolerance settings that was used while the faces were created, but there's nothing you can do to fix it automatically I think.

If you want to create closed breps from faces, then those faces must meet along their edges within absolute tolerance.

David Rutten

david@mcneel.com

Poprad, Slovakia

Permalink Reply by Fernando Conti on June 5, 2012 at 7:08am

Hi David,

I have found a solution, but it's not a happy one. Rhino 4 creates perfect solids from all the breps, and the exact same gh-project fails partially in Rhino 5. Also, Rhino 4 creates the solids a lot faster (total gh script runs faster).

(Indeed there are no gaping holes, it must have been the baking tolerance.)

But thanks for your reply!

Fernando

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