Mon Jul 8 12:13:15 EDT 2019

```You get rounding errors because it is impossible to represent exact
rotations numerically on a digital computer. Of course it is accurate
enough for real life but you can't rely vertex positions exactly meeting
for example.

Even without rotations you can't accurately stack two 0.1mm blocks because
0.1 is a recurring fraction in binary. So it is safe to union two 1mm cubes
without any overlap but not two 0.1mm cubes. One needs to understand how
numbers work on a computer to be able to avoid problems.

On Mon, 8 Jul 2019 at 16:51, Dan Shriver <tabbydan at gmail.com> wrote:

> Nate: what I was asking in the original post was how to take 1/6th of the
> hallway design my head and make 1/3.  So yes it is a mirror operation.  The
> best way to eliminate the stuff that overlapped the next octant turned out
> to be using a box.
>
> After that I take that whole shape and need to displace it and rotate it
> by 120 (I need to do that twice).
>
> Nop head: on the irrationals do I just get a rounding error or is there a
> more serious problem?  If it is a more serious problem is it possible to
> avoid it?
>
> On Mon, Jul 8, 2019 at 11:38 AM NateTG <nate-openscadforum at pedantic.org>
> wrote:
>
>> > ... So the extended discussion of the internals is interesting and
>> worthwhile but my original intent on the thread was to see if what I was
>> the three cones that were joined. ...
>>
>> The stuff in the original post doesn't seem correct to me.  It seems like
>> you're confusing rotation by 180 degrees with reflection.
>>
>> Can you try using:
>>
>> "rotate (v=[0,1,0], a=180)"
>>
>>
>> "mirror([1,0,0])"
>>
>> ?
>>
>>
>>
>>
>>
>>
>> --
>>
>> _______________________________________________