Confused as how a this could happen
Ronaldo wrote
adrian wrote
The premise is that $fn must be an integer, so you cannot have a
rotate_extrude produce an extrusion that doesn't result in a whole number
of angled segments.
Your premise is wrong. You may assign a fraction value to $fn: it will be
adjusted to an integer (with floor, I guess). If an angle is specified in
rotate_extrude, $fn is adjusted in order to ensure that the total angle is
met. See this example from above and bellow to confirm a perfect match:
My premise wasn't wrong, but my wording was. ;) Yes, I know that $fn can be
a floating point number, but it will be coerced into a integer in the
context that I was referring to.
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On 2017-01-09 15:00, adrian wrote:
cacb wrote
The premise is that $fn must be an integer, so you cannot have a
rotate_extrude produce an extrusion that doesn't result in a whole
number of
angled segments.
When you cut a cake, you will always get a whole number of slices, there
is simply no other way....
Carsten Arnholm
So given the following:
I would get this:
http://forum.openscad.org/file/n19983/my-rotate-extrude.png
Changing the last parameter in test1() to false, I would get this:
http://forum.openscad.org/file/n19983/2016-rotate-extrude.png
If you notice, in my implementation, the extrusion is broken up into 6
parts, 4 of which are 10 degrees in size and the other 2, the remaining 2
being 2.3/2 (1.15) in size. In the builtin, it is only 4 segments,
presumably 10.575 degrees in size.
I'm not saying anything is wrong with that, even if you can't control the
maximum rotation segment angle, but there is still a matter of the fit of my
implementation that I find odd. AFAICS, this should fit properly and I'm
trying to confirm that this is due to a rounding error or not.
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cacb wrote
On 2017-01-09 15:00, adrian wrote:
cacb wrote
The premise is that $fn must be an integer, so you cannot have a
rotate_extrude produce an extrusion that doesn't result in a whole
number of
angled segments.
When you cut a cake, you will always get a whole number of slices, there
is simply no other way....
Depends on your definition of "whole". You can't get half a piece as each
piece is a whole piece, but there is no stipulation that each piece must be
exactly the same size. I could cut it into 10 slices of totally different
sizes.
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adrian wrote
cacb wrote
On 2017-01-09 15:00, adrian wrote:
cacb wrote
The premise is that $fn must be an integer, so you cannot have a
rotate_extrude produce an extrusion that doesn't result in a whole
number of
angled segments.
When you cut a cake, you will always get a whole number of slices, there
is simply no other way....
Depends on your definition of "whole". You can't get half a piece as each
piece is a whole piece, but there is no stipulation that each piece must
be exactly the same size. I could cut it into 10 slices of totally
different sizes.
In any case, this question has gone beyond the original. I'm trying to
determine why there seems to be fitting errors and if they are due to
something I did or just rounding errors.
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I was writing a module to replace rotate_extrude() so that I could deal
with the issue that I mentioned in the Does rotate_extrude angle property
allow for values that don't divide 360 evenly?
http://forum.openscad.org/Does-rotate-extrude-angle-property-allow-for-values-that-don-t-divide-360-evenly-td19835.html
thread.
I still don't understand what your original issue is so I can't understand
what your replacement module is trying to do.
The angle value for rotate_extruder does not need to divide evenly into
360. The end of the object should have exactly the angle you specify. Is
that the not the case? Or is it something to do with how $fn creates the
facets that you find wrong?
On 9 January 2017 at 15:29, adrian adrianh.bsc@gmail.com wrote:
adrian wrote
cacb wrote
On 2017-01-09 15:00, adrian wrote:
cacb wrote
The premise is that $fn must be an integer, so you cannot have a
rotate_extrude produce an extrusion that doesn't result in a whole
number of
angled segments.
When you cut a cake, you will always get a whole number of slices, there
is simply no other way....
Depends on your definition of "whole". You can't get half a piece as
each
piece is a whole piece, but there is no stipulation that each piece must
be exactly the same size. I could cut it into 10 slices of totally
different sizes.
In any case, this question has gone beyond the original. I'm trying to
determine why there seems to be fitting errors and if they are due to
something I did or just rounding errors.
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The original issue is no longer an issue. Turns out that it will force the
correct angle segment size in 2016 which is close to 360/$fn such that it
will evenly divide the sweeping angle.
I was in 2015 so there wasn't an angle parameter, so I was trying to make
something that would do the same thing. That is what the above programme
does. The issue that I am pointing out here is only related to that thread
because that is how this started. Ignore that thread now.
The issue that I am having is that I am trying to determine why the code
that I wrote doesn't result in sections that fit together exactly. Is this
not working because the multiple transforms are causing the coordinate of
the objects to drift enough to see the issue that can be seen in the above
images where the surfaces are out of alignment?
Thanks,
A
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Adding a # to extrude_end_segments shows that they overlap the middle of the
object, angle wise. So I think that might be why there is a step radially.
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I am struggling to understand why it is so complicated. Why do you do the
end bits separately and not just intersect some oversized wedges with
rotate_extrude?
On 9 January 2017 at 19:35, nophead nop.head@gmail.com wrote:
Adding a # to extrude_end_segments shows that they overlap the middle of
the
object, angle wise. So I think that might be why there is a step radially.
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Something like this ?:
module pie_slice(r, start_angle, end_angle) {
R = r * sqrt(2) + 1;
a0 = (4 * start_angle + 0 * end_angle) / 4;
a1 = (3 * start_angle + 1 * end_angle) / 4;
a2 = (2 * start_angle + 2 * end_angle) / 4;
a3 = (1 * start_angle + 3 * end_angle) / 4;
a4 = (0 * start_angle + 4 * end_angle) / 4;
if(end_angle > start_angle)
intersection() {
circle(r);
polygon([
[0,0],
[R * cos(a0), R * sin(a0)],
[R * cos(a1), R * sin(a1)],
[R * cos(a2), R * sin(a2)],
[R * cos(a3), R * sin(a3)],
[R * cos(a4), R * sin(a4)],
]);
}
}
$fn = 32;
module rotate_extrude_angle(angle, radius, convexity)
intersection() {
rotate_extrude(convexity = convexity)
children();
hull()
linear_extrude(height = 1, convexity = convexity)
pie_slice(radius, 0, angle);
}
rotate_extrude_angle(angle=45, radius=1, convexity=5)
arrow_2d(1, .5, .25);
module arrow_2d(l,w,a)
{
polygon([[0,0],[w,0],[w,l-a],[w*1.3,l-a],[0,l]]);
}
On 9 January 2017 at 20:58, nop head nop.head@gmail.com wrote:
I am struggling to understand why it is so complicated. Why do you do the
end bits separately and not just intersect some oversized wedges with
rotate_extrude?
On 9 January 2017 at 19:35, nophead nop.head@gmail.com wrote:
Adding a # to extrude_end_segments shows that they overlap the middle of
the
object, angle wise. So I think that might be why there is a step radially.
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