Select and Remove Surface

Hi everybody,
I'm trying do make a 3D voronoi based structure and I would like to uncap the faces that are in contact with the borders of my box, to see the "structure" of the voronoi.

There is someway to do it?

I already tried with the dispatch command, but a can't select only the surfaces that are in contact with the box. In addition, I also tried using the inside command but I couldn't make it work.

Thanks in advance for the help

Attachments:

Voronoi.gh, 4 KB

Replies to This Discussion

Permalink Reply by Chris Tietjen on October 21, 2012 at 8:53am

Attachments:

9_3dVoronoiWithoutOuterFaces.gh, 16 KB

Permalink Reply by Manuel Oliveira on October 21, 2012 at 2:25pm

Thanks Chris,

Sorry for asking you this but, if don't cause any trouble, can you please explain me what you have you done?

Permalink Reply by Chris Tietjen on October 21, 2012 at 2:55pm

Manuel,

Since your model is a box with faces aligned with the xyz axes I used the idea that the dot product of two parallel vectors is 1 or -1. The normals of the faces that you want to remove are parallel to one of the three orthogonal axes. The dot product of these normal vectors and a vector in the direction of a particular axis allows me to distinguish which faces are the outer ones and which are not. I create three lists of faces. Each list contains the faces whose normals are not in the direction of one of the axes. I then intersect these three lists to keep only the faces that are unique to the three lists. In other words I eliminate the duplicate faces which are the outer ones.

Is this enough or should I annotate the definition?

Chris

Permalink Reply by Michael Pryor on October 21, 2012 at 3:27pm

A bit simpler with cull duplicate.

Attachments:

cull outside voronoi faces.gh, 5 KB

Permalink Reply by Chris Tietjen on October 21, 2012 at 3:50pm

I'm not seeing that culling component. Is that from Kangaroo?

Chris

Permalink Reply by Michael Pryor on October 21, 2012 at 4:03pm

its in the newest gh version. .9.0014

Permalink Reply by Chris Tietjen on October 21, 2012 at 5:41pm

Got it. Thanks. Missed that one.

Permalink Reply by Manuel Oliveira on October 21, 2012 at 3:30pm

Chris,

Thanks for the explanation, I think I got the procedure. What I still don't get it is what exactly the dot product command does.

Permalink Reply by Michael Pryor on October 21, 2012 at 3:35pm

http://en.wikipedia.org/wiki/Dot_product

Permalink Reply by Manuel Oliveira on October 21, 2012 at 4:04pm

Ok Chris, I think I got it.

What you explained to me earlier was 'cause my voronoi was in a box aligned with the x,y and z axis, you knew, in advance, the results of the dot product, (1 or -1), so, you gathered all surfaces, except the ones that the result of the dot product was 1, right?

By the way, thanks for the definition Michael, I'm still researching about it and thanks also for the link you posted, it helped a lot.

Permalink Reply by Manuel Oliveira on October 21, 2012 at 5:04pm

Sorry to bother you Michael but, can you please explain me the the logic behind the gh definition that you posted?

I get that you, in the first part of the definition (remove outside surfaces) what you are doing is to make a list with only the surfaces that are duplicated, the interior ones. How do you know that this surfaces are duplicated and the exterior ones don´t. I think if you explain this part, I will get the rest.

Thanks

Permalink Reply by Michael Pryor on October 21, 2012 at 5:58pm

Every face in a voronoi has a duplicate in the cell next to it. Unless they are exterior faces. Sinces they are duplicates they also have the same area. So we are testing which area points have 2 points in same location.