Fitting a curve to points
That limited number of measurements is due to being at the experimental
stage - if necessary, there could be many more reference points.
Your screenshots indeed show what I am trying to achieve, but HOW did
you do it?
D
On 27/07/2025 15:31, Sanjeev Prabhakar via Discuss wrote:
with the limited points available. You have to manually fit the curve.
my guess is like below, if my understanding of the points you shared is
correct.
Screenshot 2025-07-27 at 7.53.59 PM.png
Screenshot 2025-07-27 at 7.59.00 PM.png
On Sun, 27 Jul, 2025, 7:10 pm Dylan via Discuss,
<discuss@lists.openscad.org mailto:discuss@lists.openscad.org> wrote:
Example measures (in mm) for a theoretical instrument:
[[0, 50], [5, 55], [10, 50], [50, 20]]
In reality, the full length would be at least 500mm and there may be 20
or more measures.
On 27/07/2025 14:20, Sanjeev Prabhakar via Discuss wrote:
Can you share the list of coordinates
On Sun, 27 Jul, 2025, 6:38 pm Dylan via Discuss,
<discuss@lists.openscad.org mailto:discuss@lists.openscad.org
<mailto:discuss@lists.openscad.org
<mailto:discuss@lists.openscad.org>>> wrote:
I need to model musical instruments which are, basically,
flared tubes.
The attached image shows examples (these are shawms, and each
is two
pieces: the main body of the instrument and a small insert
which holds
the reed - I'm focusing on the main body.)
I have a list of measurements which are each [distance-from-end,
diameter]; effectively [x,y] or [x,z] coordinates.
Is there a way to generate a curve which passes through each
measurement
point? I have looked into bézier curves (which is how I would
approach
this in Blender) but they don't seem to function the same way
as the
curve does not pass through the given points.
Secondly, once such a curve is generated, how would I generate an
axially symmetric solid from it?
Thanks
Dylan_______________________________________________
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Ok,
So there are 4 points
you can write a function to create arc with first 3 points (counter
clockwise)
There could be another function to create an arc with the last 2 points.
last 2 points arc is clockwise with radius 50.
join the 2 arcs to get the fitting curve (you need to manually, visually
see for the continuity of the resultant curve)
once you have the curve rest is simple
On Sun, 27 Jul 2025 at 20:08, Dylan via Discuss discuss@lists.openscad.org
wrote:
That limited number of measurements is due to being at the experimental
stage - if necessary, there could be many more reference points.
Your screenshots indeed show what I am trying to achieve, but HOW did
you do it?
D
On 27/07/2025 15:31, Sanjeev Prabhakar via Discuss wrote:
with the limited points available. You have to manually fit the curve.
my guess is like below, if my understanding of the points you shared is
correct.
Screenshot 2025-07-27 at 7.53.59 PM.png
Screenshot 2025-07-27 at 7.59.00 PM.png
On Sun, 27 Jul, 2025, 7:10 pm Dylan via Discuss,
<discuss@lists.openscad.org mailto:discuss@lists.openscad.org> wrote:
Example measures (in mm) for a theoretical instrument:
[[0, 50], [5, 55], [10, 50], [50, 20]]
In reality, the full length would be at least 500mm and there may be
20
or more measures.
On 27/07/2025 14:20, Sanjeev Prabhakar via Discuss wrote:
Can you share the list of coordinates
On Sun, 27 Jul, 2025, 6:38 pm Dylan via Discuss,
<discuss@lists.openscad.org mailto:discuss@lists.openscad.org
<mailto:discuss@lists.openscad.org
<mailto:discuss@lists.openscad.org>>> wrote:
I need to model musical instruments which are, basically,
flared tubes.
The attached image shows examples (these are shawms, and each
is two
pieces: the main body of the instrument and a small insert
which holds
the reed - I'm focusing on the main body.)
I have a list of measurements which are each
[distance-from-end,
diameter]; effectively [x,y] or [x,z] coordinates.
Is there a way to generate a curve which passes through each
measurement
point? I have looked into bézier curves (which is how I would
approach
this in Blender) but they don't seem to function the same way
as the
curve does not pass through the given points.
Secondly, once such a curve is generated, how would I
generate an
axially symmetric solid from it?
Thanks
Dylan_______________________________________________
OpenSCAD mailing list
To unsubscribe send an email to discuss-
leave@lists.openscad.org <mailto:discuss-leave@lists.openscad.org>
<mailto:discuss-leave@lists.openscad.org <mailto:discuss-
leave@lists.openscad.org>>
<mailto:discuss-leave@lists.openscad.org>
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On Sunday, July 27, 2025 at 10:32:22 AM EDT, Sanjeev Prabhakar via Discuss discuss@lists.openscad.org wrote:
with the limited points available. You have to manually fit the curve.
my guess is like below, if my understanding of the points you shared is correct.
Source code for this image?
William
Glenn:
Wonderfully simple and elegant! Thank you!
Jon
On 7/27/2025 10:34 AM, Glenn Butcher via Discuss wrote:
On 7/27/2025 7:52 AM, Dylan via Discuss wrote:
I only find extrude functions, which extrude a shape along a path, or
around an existing object. I effectively need to 'spin' the curve
(path/bezier/whatever) around an axis.
rotate_extrude() in the OpenSCAD language does exactly that.
Beziers and other parametric curves will work well if you can find the
particular parameters that describe your instrument's profile. I've
been modeling steam locomotive parts, and in a lot of them the
profiles are a vexing combination of straight lines and arbitrary
curves. I found an OpenSCAD library called 'Round-Anything', has a
function called polyRound() that'll take an array of points with
attached radii and generate a set of points that replace the "pointed"
points with curves, and leave the others as they are. You can find it
here:
https://github.com/Irev-Dev/Round-Anything
There's one file there, polyround.scad, the only one you need to do
what I describe. A short code to use it to make a locomotive steam dome:
use <polyround.scad>
pts = [
[0.000,0.000,0.000],
[0.000,1.884,0.000],
[0.115,1.891,0.050],
[0.115,1.755,0.000],
[0.331,1.755,0.050],
[0.338,1.913,0.050],
[0.475,1.920,0.050],
[0.475,1.776,0.050],
[0.942,1.676,0.500],
[1.280,1.482,1.000],
[1.280,0.187,0.000],
[1.374,0.129,0.000],
[1.575,0.137,0.500],
[1.575,0.000,0.000]
];
$fn=90;
rotate_extrude(360) polygon(polyRound(pts, 20));
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Thanks. It's like those TV commercials for the hot sauce: "I use that
s&*t on everything!"
I just counted; on my steam locomotive, I used polyRound() 75 times.
Code, and a picture, are here:
https://github.com/butcherg/DRG_168
Glenn
On 7/27/2025 9:35 AM, Jon Bondy wrote:
Glenn:
Wonderfully simple and elegant! Thank you!
Jon
On 7/27/2025 10:34 AM, Glenn Butcher via Discuss wrote:
On 7/27/2025 7:52 AM, Dylan via Discuss wrote:
I only find extrude functions, which extrude a shape along a path,
or around an existing object. I effectively need to 'spin' the curve
(path/bezier/whatever) around an axis.
rotate_extrude() in the OpenSCAD language does exactly that.
Beziers and other parametric curves will work well if you can find
the particular parameters that describe your instrument's profile.
I've been modeling steam locomotive parts, and in a lot of them the
profiles are a vexing combination of straight lines and arbitrary
curves. I found an OpenSCAD library called 'Round-Anything', has a
function called polyRound() that'll take an array of points with
attached radii and generate a set of points that replace the
"pointed" points with curves, and leave the others as they are. You
can find it here:
https://github.com/Irev-Dev/Round-Anything
There's one file there, polyround.scad, the only one you need to do
what I describe. A short code to use it to make a locomotive steam dome:
use <polyround.scad>
pts = [
[0.000,0.000,0.000],
[0.000,1.884,0.000],
[0.115,1.891,0.050],
[0.115,1.755,0.000],
[0.331,1.755,0.050],
[0.338,1.913,0.050],
[0.475,1.920,0.050],
[0.475,1.776,0.050],
[0.942,1.676,0.500],
[1.280,1.482,1.000],
[1.280,0.187,0.000],
[1.374,0.129,0.000],
[1.575,0.137,0.500],
[1.575,0.000,0.000]
];
$fn=90;
rotate_extrude(360) polygon(polyRound(pts, 20));
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I will write it in openscad and send it just for the larger population here.
Nowadays I am working in python, so may not be very useful to many.
On Sun, 27 Jul, 2025, 8:59 pm William F. Adams, willadams@aol.com wrote:
On Sunday, July 27, 2025 at 10:32:22 AM EDT, Sanjeev Prabhakar via Discuss
discuss@lists.openscad.org wrote:
with the limited points available. You have to manually fit the curve.
my guess is like below, if my understanding of the points you shared is
correct.
Source code for this image?
William
The python would be most useful for me...
D
On 27/07/2025 16:44, Sanjeev Prabhakar via Discuss wrote:
I will write it in openscad and send it just for the larger population here.
Nowadays I am working in python, so may not be very useful to many.
On Sun, 27 Jul, 2025, 8:59 pm William F. Adams, <willadams@aol.com
mailto:willadams@aol.com> wrote:
On Sunday, July 27, 2025 at 10:32:22 AM EDT, Sanjeev Prabhakar via
Discuss <discuss@lists.openscad.org
<mailto:discuss@lists.openscad.org>> wrote:
with the limited points available. You have to manually fit the curve.
my guess is like below, if my understanding of the points you
shared is correct.
Source code for this image?
William
OpenSCAD mailing list
To unsubscribe send an email to discuss-leave@lists.openscad.org
Thanks, this looks like just what I need.
D
On 27/07/2025 15:34, Glenn Butcher via Discuss wrote:
On 7/27/2025 7:52 AM, Dylan via Discuss wrote:
I only find extrude functions, which extrude a shape along a path, or
around an existing object. I effectively need to 'spin' the curve
(path/bezier/whatever) around an axis.
rotate_extrude() in the OpenSCAD language does exactly that.
Beziers and other parametric curves will work well if you can find the
particular parameters that describe your instrument's profile. I've
been modeling steam locomotive parts, and in a lot of them the profiles
are a vexing combination of straight lines and arbitrary curves. I
found an OpenSCAD library called 'Round-Anything', has a function called
polyRound() that'll take an array of points with attached radii and
generate a set of points that replace the "pointed" points with curves,
and leave the others as they are. You can find it here:
https://github.com/Irev-Dev/Round-Anything
There's one file there, polyround.scad, the only one you need to do what
I describe. A short code to use it to make a locomotive steam dome:
use <polyround.scad>
pts = [
[0.000,0.000,0.000],
[0.000,1.884,0.000],
[0.115,1.891,0.050],
[0.115,1.755,0.000],
[0.331,1.755,0.050],
[0.338,1.913,0.050],
[0.475,1.920,0.050],
[0.475,1.776,0.050],
[0.942,1.676,0.500],
[1.280,1.482,1.000],
[1.280,0.187,0.000],
[1.374,0.129,0.000],
[1.575,0.137,0.500],
[1.575,0.000,0.000]
];
$fn=90;
rotate_extrude(360) polygon(polyRound(pts, 20));
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Of note, the third number in the point triple is a radius, and you have
to pay attention to the length of the adjacent lines to determine what
that should be. Also, set it to 0.0, and the point will be left alone.
On 7/27/2025 9:59 AM, Dylan via Discuss wrote:
Thanks, this looks like just what I need.
D
for the python guys
following is the code :
from openscad3 import *
a=[[0, 50], [5, 55], [10, 50], [50, 20]]
b=[translate_2d([0,x],circle(y/2)) for (x,y) in a]
l1=cpo(b)[0]
l2=arc_3p(l1[0],l1[1],l1[2],s=10)
l3=arc_2p(l1[2],l1[3],50,s=20)
sec=l2+l3[1:]
sec1=rot('x90',sec)
s1=cpo([rot(f'z{i}',sec1) for i in linspace(0,360,50)[:-1]])
s2=surface_thicken_1(s1,1)
fileopen(f'''
color("blue") for(p={[sec]}) p_line3d(p,.3);
color("magenta") points({l1},.75);
//{swp_c(s2)}
''')
For this code to run, you need to download my library openscad3.py
https://github.com/sprabhakar2006/openSCAD/blob/main/openscad3.py
If you are lucky to setup things correctly, you will be able to see the
file trial.scad
On Sun, 27 Jul 2025 at 21:14, Sanjeev Prabhakar sprabhakar2006@gmail.com
wrote:
I will write it in openscad and send it just for the larger population
here.
Nowadays I am working in python, so may not be very useful to many.
On Sun, 27 Jul, 2025, 8:59 pm William F. Adams, willadams@aol.com wrote:
On Sunday, July 27, 2025 at 10:32:22 AM EDT, Sanjeev Prabhakar via
Discuss discuss@lists.openscad.org wrote:
with the limited points available. You have to manually fit the curve.
my guess is like below, if my understanding of the points you shared is
correct.
Source code for this image?
William