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Sierpinski tetrahedron [message #13320] Tue, 01 June 2010 20:51 UTC Go to next message
avatar Wahtah  is currently offline Wahtah
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Yay, it's here! My first Shapeways model, not very original I guess, just the first thing I wanted to try, it has lots of air inside, so it's not too expensive for a model this size Smile

index.php?t=getfile&id=3732&private=0
(EDIT: the current model has been enlarged: sides 18 cm, 14.5 cm high)
The sides are about 12 cm, it's 9.5 cm high. The model has 499.994 faces, there are 4096 struts. It feels pretty sturdy, no flexibility at all of course.

(EDIT: this problem has been resolved by making the model bigger)
Though I'm pleased with the result, there are a few issues due to the thinness of the struts: struts that are in the plane of the printing layers are noticeably thicker, some of the thinnest struts (<10) didn't make it through printing and cleaning, see below:
index.php?t=getfile&id=3733&private=0

Another view:
index.php?t=getfile&id=3734&private=0

and another:
index.php?t=getfile&id=3735&private=0

Finally, I'd like to thank the good people behind POVRay and MeshLab for enabling me to make the model, and of course everybody at Shapeways, without whom this wouldn't have been possible Very Happy
Oh, and I almost forgot Sierpinski himself...

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[Updated on: Mon, 09 January 2012 09:32 UTC]

Re: Sierpinsky tetrahedron [message #13322 is a reply to message #13320 ] Wed, 02 June 2010 02:07 UTC Go to previous messageGo to next message
avatar bitstoatoms  is currently offline bitstoatoms
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Looks amazing,

well done.


Duann Scott

Re: Sierpinski tetrahedron [message #13334 is a reply to message #13320 ] Wed, 02 June 2010 21:44 UTC Go to previous messageGo to next message
avatar Ushanka  is currently offline Ushanka
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Great photos! The graph paper background is a nice touch.
Re: Sierpinski tetrahedron [message #13338 is a reply to message #13334 ] Thu, 03 June 2010 05:58 UTC Go to previous messageGo to next message
avatar Magic  is currently offline Magic
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Big model. Between level 5 and level6. Small price. Every single polygon used.
Very nice job. Congratulations!
Surprised
Re: Sierpinski tetrahedron [message #13343 is a reply to message #13338 ] Thu, 03 June 2010 11:58 UTC Go to previous messageGo to next message
avatar joris  is currently offline joris
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For some reason I still think these things are optical illusions.
Re: Sierpinski tetrahedron [message #13346 is a reply to message #13320 ] Thu, 03 June 2010 15:06 UTC Go to previous messageGo to next message
avatar Wahtah  is currently offline Wahtah
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Thanks all!

Here's a detail of the model in MeshLab, as you can see the use of faces/polygons is not extremely efficient, that's why I used so many:

index.php?t=getfile&id=3748&private=0

No two struts are the same, it took a lot of time to draw them all by hand Very Happy

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[Updated on: Thu, 03 June 2010 15:21 UTC]

Re: Sierpinski tetrahedron [message #13348 is a reply to message #13320 ] Thu, 03 June 2010 15:47 UTC Go to previous messageGo to next message
avatar Youknowwho4eva  is currently offline Youknowwho4eva
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To reduce the polygons use Rectangular trusses instead of spherical. It takes 2 polygons to make the face of a rectangle (four faces would be 8 polygons not counting the ends because your trusses are all joined), where depending on your resolution it could take hundreds (in your image it looks to be around 20) polygons to make the outside face of a cylinder.


Your friendly neighborhood Moderman
michael@shapeways.com
Re: Sierpinski tetrahedron [message #13358 is a reply to message #13320 ] Thu, 03 June 2010 19:25 UTC Go to previous messageGo to next message
avatar Wahtah  is currently offline Wahtah
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Lowering the polycount is not an issue, as long as it's below the Shapeways limit.

Actually the method I used is more suited to circular cross sections, as it will smooth everything anyway. Note the way the trusses join, in the original POVRay model those are regular cylinders joining with sharp edges.

I scanned the model in POVRay resulting in a point set of 750.000 points with normals, which MeshLab turned into a mesh of 2.000.000 faces, which I had it reduce to 500.000.

So nothing by hand of course, that would be silly...
Re: Sierpinski tetrahedron [message #13365 is a reply to message #13358 ] Thu, 03 June 2010 23:28 UTC Go to previous messageGo to next message
avatar stannum  is currently offline stannum
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What does "scanned the model in POVRay" mean?
Re: Sierpinski tetrahedron [message #13367 is a reply to message #13320 ] Fri, 04 June 2010 05:08 UTC Go to previous messageGo to next message
avatar WelshDesigns  is currently offline WelshDesigns
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"it took a lot of time to draw them all by hand"

This made me laugh, and rember a time when I was the young guy at the old aircraft factory... an old timer had to learn the new technology called CADAM, which was a drawing package at the time. He was drawing the dashed line needed for the cross section he was drafting, one little dash at a time. (like you'd do by hand right?) Later he quoted, "this cad thing will never catch on, it takes forever just to draw a dashed line". It took us a while to stop laughing, before we could tell him it was just a line type, and only one "line" was needed, not hundreds. Now I'm the old timer and the last laugh is on me I guess. Ha!
Re: Sierpinski tetrahedron [message #13369 is a reply to message #13367 ] Fri, 04 June 2010 06:59 UTC Go to previous messageGo to next message
avatar joris  is currently offline joris
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Ha ha ha, hilarious!
Re: Sierpinski tetrahedron [message #13372 is a reply to message #13320 ] Fri, 04 June 2010 08:15 UTC Go to previous messageGo to next message
avatar Wahtah  is currently offline Wahtah
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@WelshDesigns: that's classic! Laughing

@stannum: I used the povray "trace" command, which you can use to trace any line through an object. It returns both the intersection point of that line and the objects surface, as well as the surface normal at that point.

So if you use this to scan an object from the x, y and z directions you get a lot of surface points with normals, which I let povray save as an ascii .ply file, which MeshLab can read and turn into a mesh.

So scanning in the z direction means tracing rays at the model along the z axis, starting from a grid in the x/y plane. If a point is found, a new trace is started from just behind that point until no more points are found on that line. If you do this in x and y directions as well, all surfaces will be hit sufficiently.

The scanning can take quite a while, depending on the resolution and the complexity of your object, this took 1 or 2 hours.

If anyone gives a hoot I could do a tutorial with pics and code which will explain it a little better... Rolling Eyes
Re: Sierpinski tetrahedron [message #13386 is a reply to message #13372 ] Fri, 04 June 2010 18:38 UTC Go to previous message
avatar stannum  is currently offline stannum
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Thanks a lot. I used POVRay long ago, I think at that time trace was missing, because I don't remember anything like that. Time wouldn't be a new problem to me... raytraced images taking overnight was common then.

 
   
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