[OpenSCAD] General approach

Parkinbot rudolf at digitaldocument.de
Sun Jul 7 07:52:36 EDT 2019


DanS wrote
> So I'm wondering if my general approach to a problem is bad.
> To simplify I'm trying to make an arched structure where the arches change
> form.

So the best approach is to form a sequence of (morphing) polygons that
neither self intersect nor mutually intersect, skin this sequence and test
it by unioning a cube. This is what you seem to do, but only half way down.
As long as you do not skin a cross section with holes, it is straight
forward to generate polygons describing the full crossection. To exploit
symmetries, better reuse/modify a precalculated point sequence respectively
by means of list comprehension in order to compose full shaped polygons. I
think in your case this is feasible and preferable.  

While the use of Boolean ops after skinning is allowed - despite being quite
slow-, you must take care to 
1) produce proper manifolds as operands - which you don't seem to check
properly (see other thread).  
2) avoid operands using the same (or very close) points or partial identity.
OpenSCAD can have representation problems with very close vertices. 

Another hint: Try to break down complexity. Do proper testing of each
component - especially when you use polyhedron (which is called during
skin), because OpenSCADs F5 and F6 don't give semantically equivalent
output. F5 displays anything even non-valid manifolds. F12 can indicate
orientation problems, but not each and everything. 




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