curved objects

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curved objects

jon_bondy
I've seen a lot of discussions about how to design curved objects over
the years.  I know that there are 3 or 4 different approaches and
libraries, with some of these visible on Thingiverse.  But I have
trouble keeping track of all of the options, let alone recalling which
is most appropriate for a given situation.

Is there any document that summarizes approaches and libraries and gives
simple examples?  I know that some people just come up with formulas for
the shapes they wish to create, while others create shapes in InkScape
(or the like) and then use those curves to do a rotate_extrude().

I can go back and search through things, but I wondered if having a
central focus would be better for everyone in the long run

Thanks!

Stay safe!

Jon


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Re: curved objects

Leea
Yes please.

Lee

On 4/8/2020 6:05 PM, jon wrote:

> I've seen a lot of discussions about how to design curved objects over
> the years.  I know that there are 3 or 4 different approaches and
> libraries, with some of these visible on Thingiverse.  But I have
> trouble keeping track of all of the options, let alone recalling which
> is most appropriate for a given situation.
>
> Is there any document that summarizes approaches and libraries and
> gives simple examples?  I know that some people just come up with
> formulas for the shapes they wish to create, while others create
> shapes in InkScape (or the like) and then use those curves to do a
> rotate_extrude().
>
> I can go back and search through things, but I wondered if having a
> central focus would be better for everyone in the long run
>
> Thanks!
>
> Stay safe!
>
> Jon
>
>
> _______________________________________________
> OpenSCAD mailing list
> [hidden email]
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org


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Re: curved objects

nophead
"Curved objects" could mean a large variety of things. You mentioned rotate_extrude, do you mean vase type objects?

I think in general curved objects are made with the a large variety of techniques depending on the curve. I mainly use arcs hulled or extruded but sometimes 2D Bezier curves and some people use 3D Bezier curves. Sometimes I use sine waves and spirals generated by formulas. Sometimes I scan an object and import a 2D profile. For example to make a knife sheath or a box for pills.



On Thu, 9 Apr 2020 at 00:44, <[hidden email]> wrote:
Yes please.

Lee

On 4/8/2020 6:05 PM, jon wrote:
> I've seen a lot of discussions about how to design curved objects over
> the years.  I know that there are 3 or 4 different approaches and
> libraries, with some of these visible on Thingiverse.  But I have
> trouble keeping track of all of the options, let alone recalling which
> is most appropriate for a given situation.
>
> Is there any document that summarizes approaches and libraries and
> gives simple examples?  I know that some people just come up with
> formulas for the shapes they wish to create, while others create
> shapes in InkScape (or the like) and then use those curves to do a
> rotate_extrude().
>
> I can go back and search through things, but I wondered if having a
> central focus would be better for everyone in the long run
>
> Thanks!
>
> Stay safe!
>
> Jon
>
>
> _______________________________________________
> OpenSCAD mailing list
> [hidden email]
> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org


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Re: curved objects

OpenSCAD mailing list-2
I would like to see an example for the original engineering use of such
curves --- the sort of flowing lines one would see on an automobile, or
other streamlined or organic design --- but something more than just
importing a curve from Inkscape and extruding it into the 3rd dimension.

Let's consider the windshield of a 53 Corvette --- it's a simple shape, but
is made up of:

 - a curve which defines the base of the windshield
 - a curve which defines the top edge of the windshield
 - a curve which defines the center curvature of the windshield
 - curves which define the curvature of the edges from the top to the bottom

and the thickness of the glass

How would I define these mathematically in OpenSCAD and get a 3D object?

Is there a library which would do this? Could someone prepare that or
something similar as an example object if it's not already done?

I've looked, but the math and descriptions are just over my head (yes, I
know my math knowledge is deficient --- suggested reading on this would be
welcome --- I just finished _Mathematics for Everyone_ by F. Klinger, and
_Construction Geometry_ by Brian Walmsley --- ).

William



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rew
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Re: curved objects

rew
On Sun, Apr 12, 2020 at 06:01:23AM -0700, WillAdams via Discuss wrote:
> Let's consider the windshield of a 53 Corvette --- it's a simple shape, but
> is made up of:

You are saying the windshield is defined by 5 curves. This is not
necessarly true: It might be that they defined the surface and that
the four curves are defined by that surface and the intersection with
the other items. Suppose the hood and roof are flat planes and I
define the windshield to be a section of a sphere. Now the
intersecting curves are (parts of) "circles".

A class of curved surfaces are bezier surfaces. They can approximate
many useful surfaces, like for example a (part of a) sphere.

In 2D a bezier line is defined by two endpoints and two tangents at
those endpoints. In 3D a bezier surface is defined by a total of 16
control points. That windshield could very probably be just two bezier
patches stitched together. Symmetry forces that in the end there are
only 16 control points. This would be enough to create a good looking
windscreen. But if you want more control, you can split each half into
two or 4 patches and get more control to follow the original more
accurately.

I once started writing a library for bezier patches due to a message
here on this mailing list. Once I got it working I found out someone
had already mada e much more polished library that I had.

If you search for "bezier library openscad" I'm sure you'll find it.

        Roger.

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Re: curved objects

OpenSCAD mailing list-2
 Rogier Wolff <[hidden email]> wrote:

>If you search for "bezier library openscad" I'm sure you'll find it. 

Yes, I've seen it --- the problem is I've not been able to grok the documentation and successfully make use of it --- guidelines, pointers, sample code, or reference reading material suggestions would be welcome.

William



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Re: curved objects

lar3ry
You might find the documentation in the BOSL2 library more to your liking.

Library: https://github.com/revarbat/BOSL2
Wiki:     https://github.com/revarbat/BOSL2/wiki
bezier.scad: https://github.com/revarbat/BOSL2/wiki/beziers.scad




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Re: curved objects

cbernhardt
In case anyone is interested, here is a model of an early Corvette
windshield.  Most of the curvy bodywork on these early cars was designed by
calibrated eyeball on clay models and would be difficult to duplicate
mathematically.
<http://forum.openscad.org/file/t1309/vette_windshield.jpg>



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Re: curved objects

OpenSCAD mailing list-2
I'm interested --- could you post the underlying file/code?



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Re: curved objects

cbernhardt
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Re: curved objects

JordanBrown
In reply to this post by cbernhardt
On 4/13/2020 6:41 AM, cbernhardt wrote:
In case anyone is interested, here is a model of an early Corvette
windshield.  Most of the curvy bodywork on these early cars was designed by
calibrated eyeball on clay models and would be difficult to duplicate
mathematically.
<http://forum.openscad.org/file/t1309/vette_windshield.jpg> 

As it happens, Pierre Bézier was an automotive designer for Renault, and used Bézier curves to design automotive bodies.  But a bit later - mostly in the 60s.

https://en.wikipedia.org/wiki/Pierre_Bézier


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