best way to create this

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best way to create this

Leea
I am sort of new and I manage to get along but probably not in the best
or most efficient way. I marvel at some of the code I see. I want to
create this and want to know the best way. All I come up with is a
series of thin triangles in a arc, each a different size. How do I do it?



thanks
Lee




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Re: best way to create this

Whosawhatsis
If those a circular arcs, it's a really easy case for difference(). If not, you can probably still do it that way, but depending on how you want to define the curves, a chain hull might be easier.
On Feb 25, 2021, 13:44 -0800, Lee A <[hidden email]>, wrote:
I am sort of new and I manage to get along but probably not in the best
or most efficient way. I marvel at some of the code I see. I want to
create this and want to know the best way. All I come up with is a
series of thin triangles in a arc, each a different size. How do I do it?



thanks
Lee




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Re: best way to create this

adrianv
In reply to this post by Leea
I think you need to give more information about what you're trying to create.  Is the shape defined by the dimensions of the triangles?  The space between them?  Or maybe by some dimensions and some angles?  And then an altitude?   Are the arcs circles?   They don't look like it, so maybe not.  What defines the arcs?  

I think knowing exactly what you're trying to create is an important first step.  

Leea wrote
I am sort of new and I manage to get along but probably not in the best
or most efficient way. I marvel at some of the code I see. I want to
create this and want to know the best way. All I come up with is a
series of thin triangles in a arc, each a different size. How do I do it?



thanks
Lee




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Re: best way to create this

Leea
In reply to this post by Whosawhatsis
I know about Hull but what is a Chain Hull?

Lee

On 2/25/2021 3:50 PM, Whosawhatsis wrote:

> If those a circular arcs, it's a really easy case for difference(). If
> not, you can probably still do it that way, but depending on how you
> want to define the curves, a chain hull might be easier.
> On Feb 25, 2021, 13:44 -0800, Lee A <[hidden email]>, wrote:
>> I am sort of new and I manage to get along but probably not in the best
>> or most efficient way. I marvel at some of the code I see. I want to
>> create this and want to know the best way. All I come up with is a
>> series of thin triangles in a arc, each a different size. How do I do it?
>>
>>
>>
>> thanks
>> Lee
>>
>>
>>
>>
>> _______________________________________________
>> OpenSCAD mailing list
>> [hidden email]
>> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>
> _______________________________________________
> OpenSCAD mailing list
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Re: best way to create this

Leea
In reply to this post by adrianv
It is defined by the dimensions of the triangles.
I am trying to figure out how to explain it. Imagine a triangular 'rod'
that diminishes in size in all three dimensions from one end to the
other. Then bend that rod into a U shape. So it is a solid piece. The
inner arc is small and could be a circle. The outer arc is almost half a
circle but a bit elliptical. It could be circle if needed. Ideally the
hypotenuse would be a little concave but I was going to live with
straight. I was hoping a picture was worth a lot of words.

Lee

On 2/25/2021 3:59 PM, adrianv wrote:

> I think you need to give more information about what you're trying to
> create.  Is the shape defined by the dimensions of the triangles?  The
> space between them?  Or maybe by some dimensions and some angles?  And
> then an altitude?   Are the arcs circles? They don't look like it, so
> maybe not.  What defines the arcs?
>
> I think knowing exactly what you're trying to create is an important
> first step.
>
>     Leea wrote
>     I am sort of new and I manage to get along but probably not in the
>     best
>     or most efficient way. I marvel at some of the code I see. I want to
>     create this and want to know the best way. All I come up with is a
>     series of thin triangles in a arc, each a different size. How do I
>     do it?
>
>
>
>     thanks
>     Lee
>
>
>
>
>     _______________________________________________
>     OpenSCAD mailing list
>     [hidden email]
>     </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
>     http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>
>
>     curve.png (10K)
>     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>
>
>
> ------------------------------------------------------------------------
> Sent from the OpenSCAD mailing list archive
> <http://forum.openscad.org/> at Nabble.com.
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Re: best way to create this

adrianv
Your picture looked like a flat 2d picture of triangles and an arc.  So Is this sort of like what you're after?



Note: the triangles are coplanar but it doesn't look like it because of the shrinkage along the length which means the small one is not aligned with the big one.

Leea wrote
It is defined by the dimensions of the triangles.
I am trying to figure out how to explain it. Imagine a triangular 'rod'
that diminishes in size in all three dimensions from one end to the
other. Then bend that rod into a U shape. So it is a solid piece. The
inner arc is small and could be a circle. The outer arc is almost half a
circle but a bit elliptical. It could be circle if needed. Ideally the
hypotenuse would be a little concave but I was going to live with
straight. I was hoping a picture was worth a lot of words.

Lee

On 2/25/2021 3:59 PM, adrianv wrote:

> I think you need to give more information about what you're trying to
> create.  Is the shape defined by the dimensions of the triangles?  The
> space between them?  Or maybe by some dimensions and some angles?  And
> then an altitude?   Are the arcs circles? They don't look like it, so
> maybe not.  What defines the arcs?
>
> I think knowing exactly what you're trying to create is an important
> first step.
>
>     Leea wrote
>     I am sort of new and I manage to get along but probably not in the
>     best
>     or most efficient way. I marvel at some of the code I see. I want to
>     create this and want to know the best way. All I come up with is a
>     series of thin triangles in a arc, each a different size. How do I
>     do it?
>
>
>
>     thanks
>     Lee
>
>
>
>
>     _______________________________________________
>     OpenSCAD mailing list
>     [hidden email]
>     </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
>     http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>
>
>     curve.png (10K)
>     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>
>
>
> ------------------------------------------------------------------------
> Sent from the OpenSCAD mailing list archive
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Re: best way to create this

Leea
It is supposed to be 3D.

I would say the inverse of your image with the pointy tip on the inside.

Take a bowl and pull/stretch the bottom center to the right side a bit.
Then cut it in half vertically with the blade going left to right.
Trying to go from my mind to your mind without telepathy and not coming
up with the right words.

How did you do your example? Maybe I can just reverse that.

I would like to smooth it by using something better than triangles, some
shape I design with rounding.

Lee

On 2/25/2021 4:37 PM, adrianv wrote:

> Your picture looked like a flat 2d picture of triangles and an arc.
>  So Is this sort of like what you're after?
>
>
>
> Note: the triangles are coplanar but it doesn't look like it because
> of the shrinkage along the length which means the small one is not
> aligned with the big one.
>
>     Leea wrote
>     It is defined by the dimensions of the triangles.
>     I am trying to figure out how to explain it. Imagine a triangular
>     'rod'
>     that diminishes in size in all three dimensions from one end to the
>     other. Then bend that rod into a U shape. So it is a solid piece. The
>     inner arc is small and could be a circle. The outer arc is almost
>     half a
>     circle but a bit elliptical. It could be circle if needed. Ideally
>     the
>     hypotenuse would be a little concave but I was going to live with
>     straight. I was hoping a picture was worth a lot of words.
>
>     Lee
>
>     On 2/25/2021 3:59 PM, adrianv wrote:
>     > I think you need to give more information about what you're
>     trying to
>     > create.  Is the shape defined by the dimensions of the
>     triangles?  The
>     > space between them?  Or maybe by some dimensions and some
>     angles?  And
>     > then an altitude?   Are the arcs circles? They don't look like
>     it, so
>     > maybe not.  What defines the arcs?
>     >
>     > I think knowing exactly what you're trying to create is an
>     important
>     > first step.
>     >
>     >     Leea wrote
>     >     I am sort of new and I manage to get along but probably not
>     in the
>     >     best
>     >     or most efficient way. I marvel at some of the code I see. I
>     want to
>     >     create this and want to know the best way. All I come up
>     with is a
>     >     series of thin triangles in a arc, each a different size.
>     How do I
>     >     do it?
>     >
>     >
>     >
>     >     thanks
>     >     Lee
>     >
>     >
>     >
>     >
>     >     _______________________________________________
>     >     OpenSCAD mailing list
>     >     [hidden email]
>     > </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
>     >
>     http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     >    
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
>     >
>     >
>     >     curve.png (10K)
>     >     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>
>     >     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>>
>     >
>     >
>     >
>     ------------------------------------------------------------------------
>
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>     > <http://forum.openscad.org/> <http://forum.openscad.org/>> at
>     Nabble.com.
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Re: best way to create this

OpenSCAD mailing list-2
People seem to have a very hard time to imagine what you actually want.

1) Do I already have one of these in my home?
2) Is it a replacement part?
3) What does it have to mesh/interface with?
4) What are the critical or known dimensions? What dimensions don't really matter?
5) What are the critical areas in the shape? Distance between points on your drawing or radius of curves, etc.
6) If you don't bend it over, what would it look like (dimensions and important radia please)

I don't recall seeing anything like this in my house.

On 2021-02-25 6:19 p.m., Lee A wrote:
It is supposed to be 3D.

I would say the inverse of your image with the pointy tip on the inside.

Take a bowl and pull/stretch the bottom center to the right side a bit. Then cut it in half vertically with the blade going left to right. Trying to go from my mind to your mind without telepathy and not coming up with the right words.

How did you do your example? Maybe I can just reverse that.

I would like to smooth it by using something better than triangles, some shape I design with rounding.

Lee

On 2/25/2021 4:37 PM, adrianv wrote:
Your picture looked like a flat 2d picture of triangles and an arc.  So Is this sort of like what you're after?



Note: the triangles are coplanar but it doesn't look like it because of the shrinkage along the length which means the small one is not aligned with the big one.

    Leea wrote
    It is defined by the dimensions of the triangles.
    I am trying to figure out how to explain it. Imagine a triangular
    'rod'
    that diminishes in size in all three dimensions from one end to the
    other. Then bend that rod into a U shape. So it is a solid piece. The
    inner arc is small and could be a circle. The outer arc is almost
    half a
    circle but a bit elliptical. It could be circle if needed. Ideally
    the
    hypotenuse would be a little concave but I was going to live with
    straight. I was hoping a picture was worth a lot of words.

    Lee

    On 2/25/2021 3:59 PM, adrianv wrote:
    > I think you need to give more information about what you're
    trying to
    > create.  Is the shape defined by the dimensions of the
    triangles?  The
    > space between them?  Or maybe by some dimensions and some
    angles?  And
    > then an altitude?   Are the arcs circles? They don't look like
    it, so
    > maybe not.  What defines the arcs?
    >
    > I think knowing exactly what you're trying to create is an
    important
    > first step.
    >
    >     Leea wrote
    >     I am sort of new and I manage to get along but probably not
    in the
    >     best
    >     or most efficient way. I marvel at some of the code I see. I
    want to
    >     create this and want to know the best way. All I come up
    with is a
    >     series of thin triangles in a arc, each a different size.
    How do I
    >     do it?
    >
    >
    >
    >     thanks
    >     Lee
    >
    >
    >
    >
    >     _______________________________________________
    >     OpenSCAD mailing list
    >     [hidden email]
    > </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
    >
    http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
    <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
    >    
    <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
    <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
    >
    >
    >     curve.png (10K)
    >     <http://forum.openscad.org/attachment/31966/0/curve.png>
    <http://forum.openscad.org/attachment/31966/0/curve.png>>
    >     <http://forum.openscad.org/attachment/31966/0/curve.png>
    <http://forum.openscad.org/attachment/31966/0/curve.png>>>
    >
    >
    >
    ------------------------------------------------------------------------

    > Sent from the OpenSCAD mailing list archive
    > <http://forum.openscad.org/> <http://forum.openscad.org/>> at
    Nabble.com.
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Re: best way to create this

DanS
It looks like a simplified version of an amphitheater (instead of steps, the smooth hypotenuse of a triangle) where the triangle shrinks as it moves around.  The bottom side appears (in his first drawing) to be flat and flush with a horizontal surface.  Also, instead of being bent along a semicircle, as the poster mentions it is bent along a U.  The poster makes it a little more complicated by saying the curved part of the U is not circular but elliptical (and then even more complicated saying the hypotenuse should be concave).

No dimensions have been specified, relative dimensions would help.
Likewise, something describing the curvatures would also help (when you say "elliptical" do you mean like a standard ellipse, or a parabola, or hyperbolic curves....)

On Thu, Feb 25, 2021 at 9:23 PM Ron Wheeler via Discuss <[hidden email]> wrote:
People seem to have a very hard time to imagine what you actually want.

1) Do I already have one of these in my home?
2) Is it a replacement part?
3) What does it have to mesh/interface with?
4) What are the critical or known dimensions? What dimensions don't really matter?
5) What are the critical areas in the shape? Distance between points on your drawing or radius of curves, etc.
6) If you don't bend it over, what would it look like (dimensions and important radia please)

I don't recall seeing anything like this in my house.

On 2021-02-25 6:19 p.m., Lee A wrote:
It is supposed to be 3D.

I would say the inverse of your image with the pointy tip on the inside.

Take a bowl and pull/stretch the bottom center to the right side a bit. Then cut it in half vertically with the blade going left to right. Trying to go from my mind to your mind without telepathy and not coming up with the right words.

How did you do your example? Maybe I can just reverse that.

I would like to smooth it by using something better than triangles, some shape I design with rounding.

Lee

On 2/25/2021 4:37 PM, adrianv wrote:
Your picture looked like a flat 2d picture of triangles and an arc.  So Is this sort of like what you're after?



Note: the triangles are coplanar but it doesn't look like it because of the shrinkage along the length which means the small one is not aligned with the big one.

    Leea wrote
    It is defined by the dimensions of the triangles.
    I am trying to figure out how to explain it. Imagine a triangular
    'rod'
    that diminishes in size in all three dimensions from one end to the
    other. Then bend that rod into a U shape. So it is a solid piece. The
    inner arc is small and could be a circle. The outer arc is almost
    half a
    circle but a bit elliptical. It could be circle if needed. Ideally
    the
    hypotenuse would be a little concave but I was going to live with
    straight. I was hoping a picture was worth a lot of words.

    Lee

    On 2/25/2021 3:59 PM, adrianv wrote:
    > I think you need to give more information about what you're
    trying to
    > create.  Is the shape defined by the dimensions of the
    triangles?  The
    > space between them?  Or maybe by some dimensions and some
    angles?  And
    > then an altitude?   Are the arcs circles? They don't look like
    it, so
    > maybe not.  What defines the arcs?
    >
    > I think knowing exactly what you're trying to create is an
    important
    > first step.
    >
    >     Leea wrote
    >     I am sort of new and I manage to get along but probably not
    in the
    >     best
    >     or most efficient way. I marvel at some of the code I see. I
    want to
    >     create this and want to know the best way. All I come up
    with is a
    >     series of thin triangles in a arc, each a different size.
    How do I
    >     do it?
    >
    >
    >
    >     thanks
    >     Lee
    >
    >
    >
    >
    >     _______________________________________________
    >     OpenSCAD mailing list
    >     [hidden email]
    > </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
    >
    http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
    <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
    >    
    <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
    <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
    >
    >
    >     curve.png (10K)
    >     <http://forum.openscad.org/attachment/31966/0/curve.png>
    <http://forum.openscad.org/attachment/31966/0/curve.png>>
    >     <http://forum.openscad.org/attachment/31966/0/curve.png>
    <http://forum.openscad.org/attachment/31966/0/curve.png>>>
    >
    >
    >
    ------------------------------------------------------------------------

    > Sent from the OpenSCAD mailing list archive
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    Nabble.com.
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Re: best way to create this

adrianv
In reply to this post by Leea
In OpenSCAD ultimately everything is a triangle.  (Maybe you can make rectangles too?)  There are no curves.  So I'm not sure what you're hoping for about "something better than triangles".  Do you mean for the end of the shape?  

You said you want the hypotenuse a little concave?  So here's a new version.  My code is based on the BOSL2 library.  You might be able to make a shape like this without a library by subtracting a sphere from a cylinder.  It would be more symmetric, though.  The outer arc of th shape produced by the code below is *not* a circle.  

https://github.com/revarbat/BOSL2/wiki


include <BOSL2/std.scad>
include <BOSL2/skin.scad>
include <BOSL2/turtle3d.scad>
include <BOSL2/rounding.scad>

$fn=128;

width = 10;
height = 8;
curve=2;   // Amount to curve hypotenuse inward

normal = line_normal([[-height,width],[0,0]]);

//triangle = [[-height,width],[0,0],[0,width]];   // Straight side triangle

triangle = [ each arc(points=[[-height,width], [-height,width]/2+normal*curve, [0,0]]),
             [0,0],
             [0,width]
           ];

trans = turtle3d([
                   ["arc", 4, "right", 180, "shrink", 2]
                 ],transforms=true);

sweep(triangle, trans);




Leea wrote
It is supposed to be 3D.

I would say the inverse of your image with the pointy tip on the inside.

Take a bowl and pull/stretch the bottom center to the right side a bit.
Then cut it in half vertically with the blade going left to right.
Trying to go from my mind to your mind without telepathy and not coming
up with the right words.

How did you do your example? Maybe I can just reverse that.

I would like to smooth it by using something better than triangles, some
shape I design with rounding.

Lee

On 2/25/2021 4:37 PM, adrianv wrote:

> Your picture looked like a flat 2d picture of triangles and an arc.
>  So Is this sort of like what you're after?
>
>
>
> Note: the triangles are coplanar but it doesn't look like it because
> of the shrinkage along the length which means the small one is not
> aligned with the big one.
>
>     Leea wrote
>     It is defined by the dimensions of the triangles.
>     I am trying to figure out how to explain it. Imagine a triangular
>     'rod'
>     that diminishes in size in all three dimensions from one end to the
>     other. Then bend that rod into a U shape. So it is a solid piece. The
>     inner arc is small and could be a circle. The outer arc is almost
>     half a
>     circle but a bit elliptical. It could be circle if needed. Ideally
>     the
>     hypotenuse would be a little concave but I was going to live with
>     straight. I was hoping a picture was worth a lot of words.
>
>     Lee
>
>     On 2/25/2021 3:59 PM, adrianv wrote:
>     > I think you need to give more information about what you're
>     trying to
>     > create.  Is the shape defined by the dimensions of the
>     triangles?  The
>     > space between them?  Or maybe by some dimensions and some
>     angles?  And
>     > then an altitude?   Are the arcs circles? They don't look like
>     it, so
>     > maybe not.  What defines the arcs?
>     >
>     > I think knowing exactly what you're trying to create is an
>     important
>     > first step.
>     >
>     >     Leea wrote
>     >     I am sort of new and I manage to get along but probably not
>     in the
>     >     best
>     >     or most efficient way. I marvel at some of the code I see. I
>     want to
>     >     create this and want to know the best way. All I come up
>     with is a
>     >     series of thin triangles in a arc, each a different size.
>     How do I
>     >     do it?
>     >
>     >
>     >
>     >     thanks
>     >     Lee
>     >
>     >
>     >
>     >
>     >     _______________________________________________
>     >     OpenSCAD mailing list
>     >     [hidden email]
>     > </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
>     >
>     http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     >    
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
>     >
>     >
>     >     curve.png (10K)
>     >     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>
>     >     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>>
>     >
>     >
>     >
>     ------------------------------------------------------------------------
>
>     > Sent from the OpenSCAD mailing list archive
>     > <http://forum.openscad.org/> <http://forum.openscad.org/>> at
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Re: best way to create this

Leea
In reply to this post by OpenSCAD mailing list-2
1)  No you don't have one. If you did it would be easier to describe.
Two of them pushed together (one a mirror image) would make sort of an
egg holder.
2)  No
3)  Nothing
4)  Dimensions don't matter, it will vary in size.
5)  All areas are critical. Not sure how to answer this.
6)  See image

This is sort of what I am aiming for. I was wondering if there is
another way to create it. I would like the inside to be concave instead
of a hard straight slope down. I put my ugly code below that.



$fn=100;

height=20;
base=30;

for (i=[0:1:180]){
     rotate ([0,0,-i]){
         translate ([-base-3+(i/10),0,0])
         rotate ([270,0,0]){
             linear_extrude(height = 1, center = false, convexity = 10,
twist = 0)
             polygon (points=[[0,0],[0,-height+(i/15)],[base-(i/10),0]]);
         }
     }
}


Lee

On 2/25/2021 8:22 PM, Ron Wheeler via Discuss wrote:

> People seem to have a very hard time to imagine what you actually want.
>
> 1) Do I already have one of these in my home?
> 2) Is it a replacement part?
> 3) What does it have to mesh/interface with?
> 4) What are the critical or known dimensions? What dimensions don't
> really matter?
> 5) What are the critical areas in the shape? Distance between points
> on your drawing or radius of curves, etc.
> 6) If you don't bend it over, what would it look like (dimensions and
> important radia please)
>
> I don't recall seeing anything like this in my house.
>
> On 2021-02-25 6:19 p.m., Lee A wrote:
>> It is supposed to be 3D.
>>
>> I would say the inverse of your image with the pointy tip on the inside.
>>
>> Take a bowl and pull/stretch the bottom center to the right side a
>> bit. Then cut it in half vertically with the blade going left to
>> right. Trying to go from my mind to your mind without telepathy and
>> not coming up with the right words.
>>
>> How did you do your example? Maybe I can just reverse that.
>>
>> I would like to smooth it by using something better than triangles,
>> some shape I design with rounding.
>>
>> Lee
>>
>> On 2/25/2021 4:37 PM, adrianv wrote:
>>> Your picture looked like a flat 2d picture of triangles and an arc.
>>>  So Is this sort of like what you're after?
>>>
>>>
>>>
>>> Note: the triangles are coplanar but it doesn't look like it because
>>> of the shrinkage along the length which means the small one is not
>>> aligned with the big one.
>>>
>>>     Leea wrote
>>>     It is defined by the dimensions of the triangles.
>>>     I am trying to figure out how to explain it. Imagine a triangular
>>>     'rod'
>>>     that diminishes in size in all three dimensions from one end to the
>>>     other. Then bend that rod into a U shape. So it is a solid
>>> piece. The
>>>     inner arc is small and could be a circle. The outer arc is almost
>>>     half a
>>>     circle but a bit elliptical. It could be circle if needed. Ideally
>>>     the
>>>     hypotenuse would be a little concave but I was going to live with
>>>     straight. I was hoping a picture was worth a lot of words.
>>>
>>>     Lee
>>>
>>>     On 2/25/2021 3:59 PM, adrianv wrote:
>>>     > I think you need to give more information about what you're
>>>     trying to
>>>     > create.  Is the shape defined by the dimensions of the
>>>     triangles?  The
>>>     > space between them?  Or maybe by some dimensions and some
>>>     angles?  And
>>>     > then an altitude?   Are the arcs circles? They don't look like
>>>     it, so
>>>     > maybe not.  What defines the arcs?
>>>     >
>>>     > I think knowing exactly what you're trying to create is an
>>>     important
>>>     > first step.
>>>     >
>>>     >     Leea wrote
>>>     >     I am sort of new and I manage to get along but probably not
>>>     in the
>>>     >     best
>>>     >     or most efficient way. I marvel at some of the code I see. I
>>>     want to
>>>     >     create this and want to know the best way. All I come up
>>>     with is a
>>>     >     series of thin triangles in a arc, each a different size.
>>>     How do I
>>>     >     do it?
>>>     >
>>>     >
>>>     >
>>>     >     thanks
>>>     >     Lee
>>>     >
>>>     >
>>>     >
>>>     >
>>>     >     _______________________________________________
>>>     >     OpenSCAD mailing list
>>>     >     [hidden email]
>>>     > </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
>>>     >
>>> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>>> <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>>>     >
>>> <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>>> <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
>>>     >
>>>     >
>>>     >     curve.png (10K)
>>>     > <http://forum.openscad.org/attachment/31966/0/curve.png>
>>> <http://forum.openscad.org/attachment/31966/0/curve.png>>
>>>     > <http://forum.openscad.org/attachment/31966/0/curve.png>
>>> <http://forum.openscad.org/attachment/31966/0/curve.png>>>
>>>     >
>>>     >
>>>     >
>>> ------------------------------------------------------------------------
>>>
>>>
>>>     > Sent from the OpenSCAD mailing list archive
>>>     > <http://forum.openscad.org/> <http://forum.openscad.org/>> at
>>>     Nabble.com.
>>>     >
>>>     > _______________________________________________
>>>     > OpenSCAD mailing list
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>>> </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
>>>     >
>>> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>>> <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>>>
>>>
>>>     _______________________________________________
>>>     OpenSCAD mailing list
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>>> http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>>> <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>>>
>>>
>>> ------------------------------------------------------------------------
>>>
>>> Sent from the OpenSCAD mailing list archive
>>> <http://forum.openscad.org/> at Nabble.com.
>>>
>>> _______________________________________________
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>>
>>
>> _______________________________________________
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>
> --
> Ron Wheeler
> Artifact Software
> 438-345-3369
> [hidden email]
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Re: best way to create this

Leea
In reply to this post by adrianv
Daniel was real close when he said amphitheater. I wish I had thought of
that word, it would have saved a lot.

Adrianv, Yep, you got it, nailed it. I hadn't heard of BOSL so I have to
research that. Thanks much. If I figure out BOSL I can make exactly what
I want from your start.

Lee


On 2/25/2021 8:44 PM, adrianv wrote:

> In OpenSCAD ultimately everything is a triangle.  (Maybe you can make
> rectangles too?)  There are no curves.  So I'm not sure what you're
> hoping for about "something better than triangles".  Do you mean for
> the end of the shape?
>
> You said you want the hypotenuse a little concave?  So here's a new
> version.  My code is based on the BOSL2 library.  You might be able to
> make a shape like this without a library by subtracting a sphere from
> a cylinder.  It would be more symmetric, though.  The outer arc of th
> shape produced by the code below is *not* a circle.
>
> https://github.com/revarbat/BOSL2/wiki 
> <https://github.com/revarbat/BOSL2/wiki>
>
>
> include <BOSL2/std.scad>
> include <BOSL2/skin.scad>
> include <BOSL2/turtle3d.scad>
> include <BOSL2/rounding.scad>
>
> $fn=128;
>
> width = 10;
> height = 8;
> curve=2;   // Amount to curve hypotenuse inward
>
> normal = line_normal([[-height,width],[0,0]]);
>
> //triangle = [[-height,width],[0,0],[0,width]];   // Straight side
> triangle
>
> triangle = [ each arc(points=[[-height,width],
> [-height,width]/2+normal*curve, [0,0]]),
>              [0,0],
>              [0,width]
>            ];
>
> trans = turtle3d([
>                    ["arc", 4, "right", 180, "shrink", 2]
>                  ],transforms=true);
>
> sweep(triangle, trans);
>
>
>
>
>     Leea wrote
>     It is supposed to be 3D.
>
>     I would say the inverse of your image with the pointy tip on the
>     inside.
>
>     Take a bowl and pull/stretch the bottom center to the right side a
>     bit.
>     Then cut it in half vertically with the blade going left to right.
>     Trying to go from my mind to your mind without telepathy and not
>     coming
>     up with the right words.
>
>     How did you do your example? Maybe I can just reverse that.
>
>     I would like to smooth it by using something better than
>     triangles, some
>     shape I design with rounding.
>
>     Lee
>
>     On 2/25/2021 4:37 PM, adrianv wrote:
>     > Your picture looked like a flat 2d picture of triangles and an arc.
>     >  So Is this sort of like what you're after?
>     >
>     >
>     >
>     > Note: the triangles are coplanar but it doesn't look like it
>     because
>     > of the shrinkage along the length which means the small one is not
>     > aligned with the big one.
>     >
>     >     Leea wrote
>     >     It is defined by the dimensions of the triangles.
>     >     I am trying to figure out how to explain it. Imagine a
>     triangular
>     >     'rod'
>     >     that diminishes in size in all three dimensions from one end
>     to the
>     >     other. Then bend that rod into a U shape. So it is a solid
>     piece. The
>     >     inner arc is small and could be a circle. The outer arc is
>     almost
>     >     half a
>     >     circle but a bit elliptical. It could be circle if needed.
>     Ideally
>     >     the
>     >     hypotenuse would be a little concave but I was going to live
>     with
>     >     straight. I was hoping a picture was worth a lot of words.
>     >
>     >     Lee
>     >
>     >     On 2/25/2021 3:59 PM, adrianv wrote:
>     >     > I think you need to give more information about what you're
>     >     trying to
>     >     > create.  Is the shape defined by the dimensions of the
>     >     triangles?  The
>     >     > space between them?  Or maybe by some dimensions and some
>     >     angles?  And
>     >     > then an altitude?   Are the arcs circles? They don't look
>     like
>     >     it, so
>     >     > maybe not.  What defines the arcs?
>     >     >
>     >     > I think knowing exactly what you're trying to create is an
>     >     important
>     >     > first step.
>     >     >
>     >     >     Leea wrote
>     >     >     I am sort of new and I manage to get along but
>     probably not
>     >     in the
>     >     >     best
>     >     >     or most efficient way. I marvel at some of the code I
>     see. I
>     >     want to
>     >     >     create this and want to know the best way. All I come up
>     >     with is a
>     >     >     series of thin triangles in a arc, each a different size.
>     >     How do I
>     >     >     do it?
>     >     >
>     >     >
>     >     >
>     >     >     thanks
>     >     >     Lee
>     >     >
>     >     >
>     >     >
>     >     >
>     >     > _______________________________________________
>     >     >     OpenSCAD mailing list
>     >     >     [hidden email]
>     >     > </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
>     >     >
>     >
>     http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     >    
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
>     >     >
>     >    
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
>     >    
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>>
>
>     >     >
>     >     >
>     >     >     curve.png (10K)
>     >     >    
>     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>
>     >     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>>
>     >     >    
>     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>
>     >     <http://forum.openscad.org/attachment/31966/0/curve.png>
>     <http://forum.openscad.org/attachment/31966/0/curve.png>>>>
>     >     >
>     >     >
>     >     >
>     >
>     ------------------------------------------------------------------------
>
>     >
>     >     > Sent from the OpenSCAD mailing list archive
>     >     > <http://forum.openscad.org/>
>     <http://forum.openscad.org/>> <http://forum.openscad.org/>
>     <http://forum.openscad.org/>>> at
>     >     Nabble.com.
>     >     >
>     >     > _______________________________________________
>     >     > OpenSCAD mailing list
>     >     > [hidden email]
>     > </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
>     >     >
>     >
>     http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     >    
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
>     >
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>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
>     <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
>     >
>     >
>     >
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>
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best way to create this

OpenSCAD mailing list-2
In reply to this post by Leea
Not exactly sure that I understand what you want.

This is another approach where I started with a cylinder and subtracted the bits that I wanted to eliminate.

Perhaps with the right scaling and translating of the circle, you can get the shape that you want.
It will not give you triangles at the edges but will give you a nice concave pocket.

$fn=100;

height=20;
base=30;
difference(){
    cylinder(h=height,r=base);
    union(){
      translate([-100,-50,-9]){cube([100,100,base]);}
      translate([5,10,34]){scale([1,1.5,1]){sphere(r=35);}}
        }
}


If this doesn't quite give you want you want, I hope it gives you some more ideas about how to use difference and the other tools to make something by subtracting shapes.

Ron

On 2021-02-25 11:15 p.m., Lee A wrote:
$fn=100;

height=20;
base=30;

for (i=[0:1:180]){
    rotate ([0,0,-i]){
        translate ([-base-3+(i/10),0,0])
        rotate ([270,0,0]){
            linear_extrude(height = 1, center = false, convexity = 10, twist = 0)
            polygon (points=[[0,0],[0,-height+(i/15)],[base-(i/10),0]]);
        }
    }
}

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Re: best way to create this

mondo
In reply to this post by Leea
I don't see what the problem is. All you need is the artistic vision of
Michelangelo and the mathematical capabilities of Laplace, then this
type of problem is trivial. However for the rest of us....

 From your original (red?) image it looks as if it is half a cylinder,
with an the top sliced off at an angle. I would do that by making a
large cube, to slice the side off the cylinder, and rotate it to slice
off the top at an angle. If the top needs to be concave, then use a
large sphere to slice off the top. This is on the basis that if it looks
right, then it is right. If it is a one off, then nothing wrong with
getting the final shape you want by manually cutting/grinding. If the
exact shape is not necessary, then chase a shape you can more easily
generate.

On 26/02/2021 04:15, Lee A wrote:
> 1)  No you don't have one. If you did it would be easier to describe.
> Two of them pushed together (one a mirror image) would make sort of an
> egg holder.
> 2)  No
>
etc...


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Re: best way to create this

RevarBat
In reply to this post by Leea
It should be emphasized that BOSL2 is a non-backwards-compatible rewrite of BOSL, and has become far more developed than the original BOSL library.  BOSL2 code will not work with the original BOSL library.  BOSL2 is still under development, but it’s in what I’d call BETA status.


- Revar


On Feb 25, 2021, at 8:22 PM, Lee A <[hidden email]> wrote:

Daniel was real close when he said amphitheater. I wish I had thought of that word, it would have saved a lot.

Adrianv, Yep, you got it, nailed it. I hadn't heard of BOSL so I have to research that. Thanks much. If I figure out BOSL I can make exactly what I want from your start.

Lee


On 2/25/2021 8:44 PM, adrianv wrote:
In OpenSCAD ultimately everything is a triangle.  (Maybe you can make rectangles too?)  There are no curves.  So I'm not sure what you're hoping for about "something better than triangles".  Do you mean for the end of the shape?

You said you want the hypotenuse a little concave?  So here's a new version.  My code is based on the BOSL2 library.  You might be able to make a shape like this without a library by subtracting a sphere from a cylinder.  It would be more symmetric, though.  The outer arc of th shape produced by the code below is *not* a circle.

https://github.com/revarbat/BOSL2/wiki <https://github.com/revarbat/BOSL2/wiki>


include <BOSL2/std.scad>
include <BOSL2/skin.scad>
include <BOSL2/turtle3d.scad>
include <BOSL2/rounding.scad>

$fn=128;

width = 10;
height = 8;
curve=2;   // Amount to curve hypotenuse inward

normal = line_normal([[-height,width],[0,0]]);

//triangle = [[-height,width],[0,0],[0,width]];   // Straight side triangle

triangle = [ each arc(points=[[-height,width], [-height,width]/2+normal*curve, [0,0]]),
             [0,0],
             [0,width]
           ];

trans = turtle3d([
                   ["arc", 4, "right", 180, "shrink", 2]
                 ],transforms=true);

sweep(triangle, trans);




   Leea wrote
   It is supposed to be 3D.

   I would say the inverse of your image with the pointy tip on the
   inside.

   Take a bowl and pull/stretch the bottom center to the right side a
   bit.
   Then cut it in half vertically with the blade going left to right.
   Trying to go from my mind to your mind without telepathy and not
   coming
   up with the right words.

   How did you do your example? Maybe I can just reverse that.

   I would like to smooth it by using something better than
   triangles, some
   shape I design with rounding.

   Lee

   On 2/25/2021 4:37 PM, adrianv wrote:
   > Your picture looked like a flat 2d picture of triangles and an arc.
   >  So Is this sort of like what you're after?
   >
   >
   >
   > Note: the triangles are coplanar but it doesn't look like it
   because
   > of the shrinkage along the length which means the small one is not
   > aligned with the big one.
   >
   >     Leea wrote
   >     It is defined by the dimensions of the triangles.
   >     I am trying to figure out how to explain it. Imagine a
   triangular
   >     'rod'
   >     that diminishes in size in all three dimensions from one end
   to the
   >     other. Then bend that rod into a U shape. So it is a solid
   piece. The
   >     inner arc is small and could be a circle. The outer arc is
   almost
   >     half a
   >     circle but a bit elliptical. It could be circle if needed.
   Ideally
   >     the
   >     hypotenuse would be a little concave but I was going to live
   with
   >     straight. I was hoping a picture was worth a lot of words.
   >
   >     Lee
   >
   >     On 2/25/2021 3:59 PM, adrianv wrote:
   >     > I think you need to give more information about what you're
   >     trying to
   >     > create.  Is the shape defined by the dimensions of the
   >     triangles?  The
   >     > space between them?  Or maybe by some dimensions and some
   >     angles?  And
   >     > then an altitude?   Are the arcs circles? They don't look
   like
   >     it, so
   >     > maybe not.  What defines the arcs?
   >     >
   >     > I think knowing exactly what you're trying to create is an
   >     important
   >     > first step.
   >     >
   >     >     Leea wrote
   >     >     I am sort of new and I manage to get along but
   probably not
   >     in the
   >     >     best
   >     >     or most efficient way. I marvel at some of the code I
   see. I
   >     want to
   >     >     create this and want to know the best way. All I come up
   >     with is a
   >     >     series of thin triangles in a arc, each a different size.
   >     How do I
   >     >     do it?
   >     >
   >     >
   >     >
   >     >     thanks
   >     >     Lee
   >     >
   >     >
   >     >
   >     >
   >     > _______________________________________________
   >     >     OpenSCAD mailing list
   >     >     [hidden email]
   >     > </user/SendEmail.jtp?type=email&email=Discuss%40.openscad>
   >     >
   >
   http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org
   <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
   >    
   <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
   <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
   >     >
   >    
   <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
   <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>
   >    
   <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>
   <http://lists.openscad.org/mailman/listinfo/discuss_lists.openscad.org>>>

   >     >
   >     >
   >     >     curve.png (10K)
   >     >    
   <http://forum.openscad.org/attachment/31966/0/curve.png>
   <http://forum.openscad.org/attachment/31966/0/curve.png>>
   >     <http://forum.openscad.org/attachment/31966/0/curve.png>
   <http://forum.openscad.org/attachment/31966/0/curve.png>>>
   >     >    
   <http://forum.openscad.org/attachment/31966/0/curve.png>
   <http://forum.openscad.org/attachment/31966/0/curve.png>>
   >     <http://forum.openscad.org/attachment/31966/0/curve.png>
   <http://forum.openscad.org/attachment/31966/0/curve.png>>>>
   >     >
   >     >
   >     >
   >
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Re: best way to create this

Parkinbot
In reply to this post by Leea
There is a simple way to construct your amphitheater with native modules:

r1 = 100; 
r2 = 20; 
dx = 30; 
h = 80; 

intersection()
{
  difference()
  {
    translate([-dx, 0, 0]) 
      cylinder(r=r1-dx, h=h); 
    cylinder(r1=r2, r2=r1, h=h+.1); 
  }
  translate([-r1, 0, 0])cube([2*r1, 2*r1, h]); 
}


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Re: best way to create this

adrianv
You are missing the desire that the hypotenuse of the triangle be curved---a bowl shape.  I think possibly subtracting a sphere from a cylinder may work (as I suggested in my message) but it will not create a shape that is as described because the curvature will be the same on both sides and the outside shape will be circular, which is not what you get if you take a tapered triangular prism and bend it in a U shape.  So it depends on exactly what the requirements for the shape are.    

Parkinbot wrote
There is a simple way to construct your amphitheater with native modules:





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Re: best way to create this

OpenSCAD mailing list-2
The ability to scale/distort the sphere prior to subtracting it from the cylinder gives some more flexibility in the shape of the resulting amphitheater.

On 2021-02-27 11:03 a.m., adrianv wrote:
You are missing the desire that the hypotenuse of the triangle be curved---a bowl shape.  I think possibly subtracting a sphere from a cylinder may work (as I suggested in my message) but it will not create a shape that is as described because the curvature will be the same on both sides and the outside shape will be circular, which is not what you get if you take a tapered triangular prism and bend it in a U shape.  So it depends on exactly what the requirements for the shape are.    

Parkinbot wrote
There is a simple way to construct your amphitheater with native modules:





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Re: best way to create this

adrianv
That's true.  But the outside boundary of the shape you get by bending the rod is a spiral, not a simple transformation of a circle.  You can make a spiral edged "cylinder" using linear_extrude and trigonometry.  But how do you transform the sphere to align properly with a spiral edge?  It's not at all clear how you do that.   I don't think it's going to be a linear transformation.  

There's a certain point where struggling to make the primitives do something just doesn't make sense when you can directly do the thing you want with "advanced" methods in a simple and straight forward way.  This is part of the reason why I'm interested in developing and implementing those "advanced" methods:  they may be difficult to implement but they aren't necessarily "advanced" to use.  For this problem a lot depends on the actual goals of the original poster.  Those goals were not clearly articulated.  Maybe subtracting a sphere from a cylinder is good enough.  Maybe it's even a better result, more closely aligned with the desires of the original poster.

Here's an image of the bottom of the shape obtained by bending the tapered rod:



OpenSCAD mailing list-2 wrote
The ability to scale/distort the sphere prior to subtracting it from the
cylinder gives some more flexibility in the shape of the resulting
amphitheater.

On 2021-02-27 11:03 a.m., adrianv wrote:

> You are missing the desire that the hypotenuse of the triangle be
> curved---a bowl shape.  I think possibly subtracting a sphere from a
> cylinder may work (as I suggested in my message) but it will not
> create a shape that is as described because the curvature will be the
> same on both sides and the outside shape will be circular, which is
> not what you get if you take a tapered triangular prism and bend it in
> a U shape.  So it depends on exactly what the requirements for the
> shape are.
>
>     Parkinbot wrote
>     There is a simple way to construct your amphitheater with native
>     modules:
>
>
>
>
>
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Re: best way to create this

Parkinbot
In reply to this post by adrianv
It is always a question of the specification. In this case the TS gave a drawing showing a kind of bagel with triangular crossections. If the spec would show some curved sections, one would have to see, whether it could be done with scaling al sphere or a rotate_extrude() ...

What I wanted to point out (with my last two posts) is that one should not disregard the elegance of native solutions, especially when giving advice to novice programmers.



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