Dan Shriver tabbydan at gmail.com
Mon Jul 8 13:52:37 EDT 2019

```Thanks nop head:  I was just concerned because people were saying "barf"
etc.
Small errors, loss in precision, are acceptable to me.  I just don't want a
rotation to take a previously valid model and make it invalid.

On Mon, Jul 8, 2019 at 12:14 PM nop head <nop.head at gmail.com> wrote:

> 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])"
>>>
>>> ?
>>>
>>>
>>>
>>>
>>>
>>>
>>> --
>>>
>>> _______________________________________________
>>>
>> _______________________________________________