Forums Houdini Indie and Apprentice Scatter objects on the center edges of another and aligned to that also.

Scatter objects on the center edges of another and aligned to that also.

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Houourin
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Hi there,
A newbie here. Nice to meet you all.
I hope you can help me with this one.

Problem:
I have an sphere ( poly ) and in every edge of that sphere I want to scatter a cylinder. Like to perform a wireframe view.
I want it to be scattered and not go for a “wireframe solution” because later I will need to do more things with that scattered cylinder… the final result is to create a Dome Tent. so I will need to add screw and stuff in the edges. etc…


Things I tried:
First I simplified my self the job and started with just a plane. I divide it to get the triangles.
I resampled the plane, so I get points in the middle of every edge but the Copy node, won't read the alignment properly..
I also tried with the carve node.
But I'm kind of stuck, searching/testing for different things with much idea of what I'm doing. hehe.
I've been reading in the forum some people scattering objects on edges of a spline, but this solution didn't work for my case, because I need to remove the points in the connections also, so there won't scatter anything.

Well… is that complicated? am I aiming to high? should I do it by hand this time?
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howiem
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Newb here, too. Pleased to meet you

Not quite clear on why you want to scatter - Scatter op is usually when you want randomness to the points' positions.

One issue you'll have is that in a poly (geodesic) sphere the edges aren't all the same length.

Had a quick play, though; definitely not there yet, but there might be some clues in there. Note the use of Poly Frame, with the Tangent attribute changed to N - this gives you normals that are actually tangential. Also the use of primpoints in the Group Expression to find all the points connected to only 4 others (which happen to be the structure's midpoints)

There are issues (rotation of some of the tubes is wrong) but I ran out of time.

Suspect if you're trying to create a tent you may be best off with a poly wire approach, then add stuff to the points after. (Note the weirdness: to delete all the primitives in a bit of geometry, but leave the points, you need to use the Add SOP. That's Houdini for you

Attachments:
almost.hiplc (71.7 KB)

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ignaciox10s
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hello howiem,

Thank you for your approach, while I was waiting for the approval of the message in the forum by the admin, ( It was my very first message ) I tried different things, and you were right. Poly Wire makes much more sense.
my approach of scatter things in the middle of the edges was a pain to control, I'll take a look to your file. at least while trying that way I could learn something. and sure from your file I can learn much more! thanks!

I already trimmed a bit the poly wires, so there is space in the joints. And now I just need to scatter objects in the points so there is the connections.

But! new challenge for me.. there is points with 5 edges and others with 6 edges… now just trying to find a way to scatter one object only if the point has 5 or 6 vertex under it… lets see if I can get far with that.

Thankyou a lot!
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howiem
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But! new challenge for me.. there is points with 5 edges and others with 6 edges… now just trying to find a way to scatter one object only if the point has 5 or 6 vertex under it… lets see if I can get far with that.

Look at the Group by expression SOP in my file: it adds all the points that have 4 connections to them to the group, using the handy pointprims function (which returns an array of any primitives making use of the current point). Change that 4 to a 5. Now you can use that group in a Copy to points SOP to only copy your mesh to one set of points. Duplicate the Copy SOP, stick an exclamation mark in front of the group name - !group1 - to copy only to the points that aren't in the group. Merge the results
Edited by howiem - 2018年1月24日 10:39:46
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ignaciox10s
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Thankyou!

Thats cool, I'll take a look into that!
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balthou1703
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Found out in Vex details:

i[]@pts;
int n = 0;

for(n;n<i@toto;n++)
{
    p1 = point(0,"P",n);
    append(@pts,n);
    i[]@nei = neighbours(0,@pts[n]);
    for(int l = 0; l<len(@nei) ; l++)
    {
      p2 = point(0,"P",@nei[l]);
      edge = (p2+p1)/2;
      v[]@arredge;
      push(@arredge, edge);

    }
}

int Count, Count_A;


for(Count = 0; Count < len(@arredge); Count++)
    {
    for(Count_A = 0; Count_A < len(@arredge); Count_A++)
        {
        if( (@arredge[Count] == @arredge[Count_A]) && (Count != Count_A) )
            {
            removeindex(@arredge, Count_A);
            }
        }
    }


for(int v=0; v<len(@arredge); v++)
{    
    addpoint(0, @arredge[v]);
}
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