[OpenSCAD] STL without render?

nop head nop.head at gmail.com
Thu Jun 2 12:35:26 EDT 2016


Simply replacing the unions with a cylinder by a hull of two spheres will
probably give a decent improvement in speed. Unioning a sphere with a
cylinder can be very slow.

On 2 June 2016 at 15:29, Parkinbot <rudolf at parkinbot.com> wrote:

> bsuter wrote
> > In that post you wrote "A single sweep() along a smoothed trajectory
> > will be faster than a union of cylinders and spheres describing the
> > same". Could you please explain further what you mean, in OpenSCAD
> > terms, by "single sweep() along a smoothed trajectory"?
>
> This code is a good starting point and show case:
> http://www.thingiverse.com/thing:547620/#files
> to get an idea, how sweeps behave. The (implicit) union() is needed for
> marriage of different sweep trajectories.
>
>
> > Certainly each of my branches can be modeled as a sequence of
> > nodes, where each node has an associated radius. Is there a way to
> > represent this directly in OpenSCAD? I.e. to specify a trajectory in
> > 3D, and then extrude (ideally a circular cross-section, but a polygon
> > would work too) along this trajectory, with the extrusion radius
> > defined at each node?
>
> There is no language support for general extrusion along trajectories, and
> there is no data structure support (or let's say only weak array support)
> for things like trees and so on. But there are libraries like sweep() and
> skin() going into this direction. Also see here:
> http://www.thingiverse.com/thing:900137
>
>
> >> I've implemented some Matlab class to generically describe arteries with
> >> an
> >> interpolation scheme. The output is a winding 'wire' in 3D with free
> >> radius
> >> at each point in STL-format.
>
> this is an example of the outcome:
> http://forum.openscad.org/Non-Linear-Transformations-tp14539p14597.html
>
> The class simply does some nspline calculation over a sequence of 4D
> vectors
> (x, y, z, r) describing a skeleton line. Most of the code is for handling
> STL-triangulation and output.
>
>
> >> In lack of an own union or furcation operator
> >> capable to do the intersection triangulation we currently use OpenSCAD
> >> and
> >> Blender to compose porperly placed wires into tree structures which we
> >> again
> >> cut into puzzle pieces for 3D print.
> > This part I don't understand ;(
>
> STL triagulation is easy and fast if you don't have to check for
> self-intersection (SI). I.e. if the code can assume, no SI will happen, it
> can skip all tests and calculations that would be needed to treat SI and
> just knit some generic triangulation pattern in a straight forward manner.
> Its helps to think about physical knitting to understand what is going on.
> For the puzzle part: It might be interesting to print a structure in
> pieces,
> e.g. to compose a construction kit or similar (which can also be used for
> moulding).  In your case, it might be advantegous to print the neurons and
> the dendrits as destinct pieces and design a connector for piecing parts
> together as puzzle.
>
> A union of any non-SI shapes might be SI - and will be SI at defined
> locations in the case of furcations and trees. So, if SI is only happening
> at furcation points, the intersection can be calculated somehow in a fast
> manner, to get a proper triangulation. Have a look, how the union of two
> cylinders is mapped into STL (to get a first impression, you can use F10
> and
> Ctrl+1 which only partly triangulates).
> This is the principle. OpenSCAD has this operator in form of union(). So,
> one way is to import a bunch of branches (STLs) already correctly placed
> und
> let OpenSCAD do the work dirty work in a general way.
> In fact at CSG-level (F5) this is done only virtually by the graphics card.
> And when it comes to STL output (F6) CGAL is used, which takes its time.
>
> Knowing that all your branches will not SI, except at furcation points, you
> can write your own specialized (and thus fast) union() that remeshes just
> the furcation intersection part of the branches.
>
>
> > My main goal is (a) virtual reality visualization of many neurons
> > together, and (b) 3D printing of individual neurons.
>
> It depends on how often this is repeated. If you model just some two or
> three examples, long CGAL rendering times for that what you have, might be
> tolerable, as recoding consumes much more time.
>
> For virtual visualization you might want to put in more effort. OpenSCAD
> has
> some nice animation support on the CSG-level. Trygon used it to do some
> amazing things.
> http://forum.openscad.org/Product-Video-produced-with-OpenSCAD-td15783.html
> .
> Much more of course is offered by Blender.
>
> Rudolf
>
>
>
>
> --
> View this message in context:
> http://forum.openscad.org/STL-without-render-tp17503p17530.html
> Sent from the OpenSCAD mailing list archive at Nabble.com.
>
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