[OpenSCAD] Evaluating imported STL's

Ronaldo rcmpersiano at gmail.com
Thu Jun 16 17:26:25 EDT 2016


I had taken mistakenly your scale(0) sphere(). I had assumed (without
testing it) that it is incorrectly evaluated as an empty set. But no, it is
a point: the origin! Preview that:

> hull() {
>     sphere(5);
>     translate([0,0,12]) scale(0) sphere();
> }

The result is mathematically correct: the convex hull of the sphere(5) with
the point [0,0,12]. So, scale(0) (or equivalently your multmatrix stuff)
transform anything into a point, the origin, in a way that can be
translated, rotated and scaled again.

Why didn't you get anything in the stl file? Because there is no facets in
scale(0) sphere() just one vertex.


> minkovsky() {
>     cube(5);
>     translate([0,0,12]) scale(0) sphere();
> }

 is equivalent to translate([0,0,12])  cube(5), which is correct because
scale(0) sphere() is not the empty set.

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