[OpenSCAD] Twisted Torus

Tim V. Shaporev tim.shaporev at auriga.ru
Tue Oct 9 12:11:44 EDT 2018

How many steps do you want in a loop?

for (i=[0:N-1]) [ cos(360*i/N),


for (i=[1:N]) [ cos(360*(i-1)/N),

something like that...

On 10/9/2018 5:52 PM, Zacariaz wrote:
> Ronaldo wrote
>> Nice done. Just 3 cents:
>> a) there is a predefined variable PI in the language;
>> b) it is usually advisable to avoid a float as increment of a for;
>> c) the computation of the polyhedron vertices could be simply:
>> p =
>>      [
>>      for( ta = [0:360/s2:359] )
>>        for( i = [ta:360/seg:ca+ta] )
>>              [
>>                  -sin(ta)*(cos(i)*r1+r2),
>>                  cos(ta)*(cos(i)*r1+r2),
>>                  sin(i)*r1
>>              ]
>>      ];
> As for your first point, good to know. Don't know how I've missed it, but in
> this case it doesn't actually matter as it cancels out. It was more for
> explanatory purposes.
> Secondly I get what you're saying, and believe you me I've ha a lot of
> trouble getting the for loops in openscad to behave. The first for loop
> defining p pretty much explain the issue.
> When working with integers, there really is not issue, because you can
> always just say
> for( [begin:step:end-1] )
> to get the actual range you're looking for, but if your step is not and
> integer, in this case 360/s, you need to go to extremes ot make it work,
> like
> for( [0:360/s:360-360/s] )
> which can course problems due to floating point "errors", and don't even get
> me started on the case that the loop doesn't start at 0, in which case
> you'll have to ensure that you start at a multiple of 360/s, which is pretty
> much impossible, when working with floating point values.
> I actually did plan to ask what to do in such situations, because it goes
> without saying that sometimes 360 iterations just isn't enough to achieve
> the desired resolution, so to speak.
> Personally I'm used to the C syntax and would much rather have written
> for( i = 0; round( i, 3 ) < 360; i += 360/s ) // 3 decimals should be ample
> resolution.
> and I don't see how to achieve the same effect with openscad syntax, without
> going to extremes.
> Lastly, what about the center point? I know it isn't strictly needed when
> splitting the torus in 2, but I do believe it increases the quality, and it
> certainly is need if you wish to split it into 3 or more, or simply use some
> arbitrary angle.
> Or am I missing something?
> And also thanks. To be honest, I can't help to be a little bit proud of
> myself. Regardless, I do plan to try again from scratch, to see if I can't
> do a better job of it.
> --
> Sent from: http://forum.openscad.org/
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