"We can make solid surfaces by reducing the step size so the cylinders
overlap but its slow and the result is poor. A better approach is to use
hull() to join adjacent cylinders.

module slice(x,thickness) {
assign(pa = f(x))
assign(pb = g(x))
assign(length = norm(pb-pa))
orient_to(pa,pb-pa)
cylinder(r=thickness,h=length);
};

module ruled_surface(limit,step,thickness=1) {
for (x=[0:step:limit-step])
hull() {
slice(x,thickness);
slice(x+step,thickness);
}
};"

from here:

http://kitwallace.tumblr.com/post/85509667344/surfaces-rule-ok

which refers, I think, to the image just above the code.

I get:

"WARNING: No top level geometry to render"

There's a rest of the story.  I have no clue.

I've been looking long and hard for something like this.

I'd really like it to work.

Anyone?

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P.S.

I'm in Linux (Linux Mint), using Openscad v2014.03.

Anything newer, I have not been able to get to work.

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P.P.S

I think it's either a ruled paraboloid or a doubly ruled surface hyperbolic
paraboloid:

https://en.wikipedia.org/wiki/Paraboloid#mediaviewer/File:Hyperbolic-paraboloid.svg

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You copied only half of the code you linked to.
If you include the remaining part of his code it works as it should.

-Marius

Well, I think this is all the code there is:

module orient_to(origin, normal) {
translate(origin)
rotate([0, 0, atan2(normal.y, normal.x)]) //rotation
rotate([0, atan2(sqrt(pow(normal.x, 2)+pow(normal.y, 2)),normal.z),
0])
child();
}

module ruled_surface(limit,step) {
for (x=[0:step:limit])
assign(pf = f(x))
assign(pg = g(x))
assign(length = norm(pg  - pf))
orient_to(pf, pg - pf)
cylinder(r=Line_radius,h=length);
};

function f(a) = [ Radius * cos(a),
Radius * e * sin(a),
0];
function g(a) = [ Radius * cos(a+Phase),
Radius * e * sin(a + Phase),
0]
+ [0,0,Height];

Phase = 120;
Height = 60;
Radius = 20;

Line_radius=1.5;
e=1.5;
Step=10;
ruled_surface(360,Step);

function norm(v) =
pow(v.xv.x + v.yv.y + v.z*v.z,0.5);

function f(x,p) = [0,0,xHeight];
function g(x,p) = [Radius * cos(x360Revs),
Radius * sin(x360Revs),
xHeight];

Height=60;
Radius=20;
Revs=2;
Steps=200;
Step=1/Steps;
Thickness=1;
Sides=10;

$fn= Sides;
ruled_surface(1,Step,Thickness);

module orient_to(origin, normal) {
translate(origin)
rotate([0, 0, atan2(normal.y, normal.x)]) //rotation
rotate([0, atan2(sqrt(pow(normal.x, 2)+pow(normal.y, 2)),normal.z),
0])
child();
}

module ruled_surface(limit,step,params) {
for (x=[0:step:limit])
assign(pf = f(x,params))
assign(pg = g(x,params))
assign(length = norm(pg-pf))
orient_to(pf,pg-pf)
cylinder(r=Line_radius,h=length);
};

function f(a,phase) = [ Radius * cos(a),
Radius * e * sin(a),
0];
function g(a,phase) = Top_ratio * [ Radius * cos(a+phase),
Radius * e * sin(a + phase),
0]
+ [0,0,Height];

Phase=120;
Height = 60;
Radius = 20;

Line_radius=1.5;
e=1.5;
Top_ratio = 0.8;

Step=20;

union(){
ruled_surface(360,Step,Phase);
ruled_surface(360,Step,-Phase);
}

function f(x,p) = p[0] + x/Length * (p[1] - p[0]);
function g(x,p) = p[2] + x/Length * (p[3] - p[2]);

Length=40;
Width=40;
Height=60;
Steps=10;
Step=Length/Steps;
Thickness=3;
Sides=10;
p = [
[0,0,0],
[0,Width,0],
[Length,Width,0],
[Length,0,0],
[0,0,Height],
[0,Width,Height],
[Length,Width,Height],
[Length,0,Height]
];

$fn= Sides;
ruled_surface(Length,Step,Thickness,[p[0],p[2],p[5],p[7]] );
ruled_surface(Length,Step,Thickness,[p[0],p[5],p[2],p[7]] );

module slice(x,thickness) {
assign(pa = f(x))
assign(pb = g(x))
assign(length = norm(pb-pa))
orient_to(pa,pb-pa)
cylinder(r=thickness,h=length);
};

module ruled_surface(limit,step,thickness=1) {
for (x=[0:step:limit-step])
hull() {
slice(x,thickness);
slice(x+step,thickness);
}
};

Put it all together.

Here's what I've got:

"WARNING: No top level geometry to render"

Now which half and how, still a mystery.

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You just pasted a whole bunch of mixed-up code.
If you read the article and use the components as described, you should have more luck.
e.g. the hyperboloid code from the article appended verbosely below.

-Marius

module orient_to(origin, normal) {
translate(origin)
rotate([0, 0, atan2(normal.y, normal.x)]) //rotation
rotate([0, atan2(sqrt(pow(normal.x, 2)+pow(normal.y, 2)),normal.z), 0])
child();
}

module ruled_surface(limit,step) {
for (x=[0:step:limit])
assign(pf = f(x))
assign(pg = g(x))
assign(length = norm(pg  - pf))
orient_to(pf, pg - pf)
cylinder(r=Line_radius,h=length);
};

function f(a) = [ Radius * cos(a),
Radius * e * sin(a),
0];
function g(a) = [ Radius * cos(a+Phase),
Radius * e * sin(a + Phase),
0]
+ [0,0,Height];

Phase = 120;
Height = 60;
Radius = 20;

Line_radius=1.5;
e=1.5;
Step=10;
ruled_surface(360,Step);

Hey, I don't know why you felt you had to delete your posts but we're all
friends here so you shouldn't feel that you have anything to hide.
We all had to ask for help at one point and reading these conversations is a
great way to learn. In any case, this discussion forum is a bit different
from most in that it is actually just a layer on top of a mailing list – all
posts are automatically sent to all subscribers so deleting posts has a
limited effect (there was nothing I could see that warranted your
self-moderation by the way).

Anyway, we hope you enjoy exploring the capabilities of OpenSCAD and look
forward to helping you with your next query. :-)

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Indeed , as the author of the article and code in question, I would have been
interested to see what problems you were having with the code so I can
improve the article.

Chris

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