On Sun, 22 Nov 2015 16:15:15 -0700 (MST)
Jimmis98 anonimos79violin@gmail.com wrote:

OpenSCAD can't do it, but for a uniform material Meshlab can. See

http://gazebosim.org/tutorials?tut=inertia&cat=build_robot

As far as I know, there is no short way to find the COM of a model.

Of course, if the model is of uniform density, then the center of mass is
just related to the center of volume. You could find the volume of each
item in your assembly, and then scalar multiply that by the translation
vectors, add them all together, and divide by the total mass to get the COM.

In general, OpenSCAD does not have functions which ask questions about the
model that has been made.

Good luck.

On Sun, Nov 22, 2015 at 6:15 PM, Jimmis98 anonimos79violin@gmail.com
wrote:

I would love to have some functions that calculate information about the
model:
facets,
edges,
estimated hard disk space for a given export e.g. storage_space(type="stl")
volume,
surface area,
principal rotation axes, (output as a matrix?)
center of mass,
surface area that intersects a given plane,
a way to get a point plane or line segment on the surface of a 2D or 3D
shape (im thinking some way that we could at least find the farthest or
nearest point to the center of mass),
contour length of a slice intersecting a given plane,
estimated filament volume as a function of shell thickness and fill
percentage (although we could do that ourselves with the above functions)

It would also be nice if each of these functions could work on a tree of
code e.g.

module widget(){...}
f=facets(widget());
echo(f);

and if no code were passed to facets() then it would calculate it based on
the whole model.

I would, of course, also like: them to be implemented in the next release,
with good documentation, in the exact method i described, and a pony.
kthxbai.

On Mon, Nov 23, 2015 at 9:57 AM, clothbot andrew@plumb.org wrote:

On 11/23/2015 04:52 PM, Ari Diacou wrote:

Hmm, most of that information (when applied to the final rendered model)
could be generated by some post processing. This could be a nice candidate
for a very simple plug-in interface as discussed in a different thread.

I think there's an issue on github asking for something in that
direction. With a more general approach, it could cover lots of things
(e.g. call a slicer, upload to some webservice like octoprint, calculate
information).

All that would mean it's strictly a GUI feature, the language itself
does not need to know anything about this.

No unicorn? Where's the challenge then? ;-)

ciao,
Torsten.

I was hoping for them inside the language.

Most of these things I wanted when I was designing this thing:
http://www.thingiverse.com/thing:487090/#files

It was a climbing hold for a rock wall. The basic code was:

module rock(){
hull(){
for(i=1:n){
translate(random_3_array[i])
sphere(r=random_size[i]);
}
}
}

module hold(){
difference(){
rock();
translate([0,0,-about half the size of rock()])
cube(slightly larger than the size of rock()) //cuts off
bottom half of rock
bore(); //so I can drill a bolt into it
}
}

But because this was before list manipulations, I had no idea how big my
random blob was going to be, or how far down I should drill the bore.

These are the kinds of operations that would be far easier if I had access
to them in the language, rather than as a plugin.

Or am I misunderstanding, and plugins could could be accessed in-language
somehow?

On Mon, Nov 23, 2015 at 11:14 AM, Torsten Paul Torsten.Paul@gmx.de wrote:

On Mon, 23 Nov 2015 09:31:59 -0700 (MST)
Jimmis98 anonimos79violin@gmail.com wrote:

Yeah - just export the model as STL and load it into the relevant tool
like meshlab. There are lots of things OpenSCAD doesn't do - and in most
cases that is a good thing.

Alan

On 11/23/2015 11:40 AM, Ari Diacou wrote:

You can create constants (a.k.a "variables") from the random values,
then use their values (perhaps in vectors) to build / translate rocks &
holes & slicing planes:

RockOD = rands(20,50,1)[0];
HoleOD = rands(3,5,1)[0];
HoleSides = rands(3,8,1)[0];

echo(str("Rock dia: ",RockOD));
echo(str("Hole dia: ",HoleOD));

difference() {
sphere(d=RockOD);

cylinder(d=HoleOD,h=2*RockOD,$fn=HoleSides,center=true);

 translate([0,0,-RockOD/2])
     cube([2*RockOD,2*RockOD,RockOD],center=true);

}

Granted that you can't reach into the model to get mesh features, but
you can certainly use the /dimensions/ of the overall structure, because
you know them already!

--
Ed
softsolder.com