Peter,

your work looks great! However, can you explain what you did exactly? Did
you use the sweep function or what do you mean by chain hulling your
elements? I am not that advanced :D

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Chain-hull is a old but very intuitive way to sweep a cross-section along a
path.
You place the cross-section (linear_extruded by a small height of e.g.
e=0.05, so that it is a 3d-object. As hull() in 3d only takes 3d-objects)
at the start and the next 2nd cross-section a small distance along the
path. Then you do a hull() to connect them. Now place the 2nd and the 3rd
cross-section and hull them together. And so on ...
Now, hull() on a concave cross-section would smooth out the edges, so you
need to build up your piece by chain-hulling parts that are all convex.

Now to see whats going on in my code, just replace all the hull() commands
with union(); you will then see all the cross-section.

I hope this makes things clear.

Using the algorithm I described  here
http://forum.openscad.org/Two-annoyances-td12935i20.html#a13110  , this
is what I come up :

http://forum.openscad.org/file/n13369/Screenshot_sweep_ring.png

The approach can start at any point in the space (so, forget about [0,0,0] )
and
sweeping through any path onto any direction (so, forget about X-Y-Z).

The figure shown is sweeping through a circle, not an ellipse. But it will
work
the same way.

$  Runsun Pan, PhD

$ -- libs: doctest , faces ( git ), offliner ( git );

tips: hash( 1 , 2 ), sweep , var

$ -- Linux Mint 17.1 Rebecca x64  + OpenSCAD 2015.03.15/2015.04.01.nightly

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Thanks Peter,

your approach helped me a lot understanding more in OpenSCAD. I finally
managed to create a good ellipsoid shape, if you want to check it out, see
here
http://forum.openscad.org/Tough-Nut-How-to-get-text-on-this-ellipse-shape-td13430.html
.

Patrick

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