LOL!  Thanks!  I just got the surfaces separated last night. Today I
flatten them.  It has been entertaining.  I've made lots of mistakes!

The specific application I have in mind involves accepting 3D designs
that were created using tools other than OpenSCAD, meaning that I need
to be able to work on STL files, so I'm not sure how many of the
OpenSCAD solutions that have been offered would be suitable.  I suppose
one could convert an STL file into a polygon using an external script,
but doing it all in one place in one program seems best for me.

I was going to do as you did (take each triangle and rotate it and shift
it to flatten it to the existing surface) but I am now thinking I will
just create a new set of triangles on a plane directly.

:)

On 12/28/2016 10:18 PM, Parkinbot wrote:

jon_bondy wrote

Yeah. It is a trival IO-converter that picks the "normal" (optional) and
"vertex" lines and inserts some brackets and commas around and between the
numbers to get scad-Code.
A (masochistic) purist could also augment a pair of string quotes at the
beginning and the end of the STL and then try to parse the file with
OpenSCAD using an import like this:

to enter the "rich" world of OpenSCAD's string manipulation. If have done
that a while ago just for fun to find out how much you can squeeze out of
OpenSCAD's string processing. The runtime was so poor (~3 minutes for a
200kB stl) that I never finished the code to also parse exponents. Anyone,
who is interested in it, can find the code attached and try to parse a
simple stl like a cube or a sphere with it.

jon_bondy wrote

I wonder how you will implement the word "just" without parsing your STL
into a common-edge topology tree and unrolling this tree.

parse_stl.scad http://forum.openscad.org/file/n19816/parse_stl.scad

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My thought is to locate an edge triangle, and use recursion to go
through all of the other triangles.  The first triangle will be placed
on the z=0 plane, and subsequent triangles will be placed next to the
previous triangle, just by knowing the shape of the triangle.

We will see.  It's been a bumpy ride, and this may be just another bump.

Jon

On 12/29/2016 9:41 AM, Parkinbot wrote:

What happens if you have a curve in more than one dimension that can't be
flattened without tares in it?

On 29 December 2016 at 15:12, jon jon@jonbondy.com wrote:

I imagine that you are correct.  It happens that the particular
application I am working with assumes that each surface is a portion of
a cylinder, so it only curves in one direction.

On 12/29/2016 10:19 AM, nop head wrote:

jon_bondy wrote

that is a correct approach. But it needs to build a common edge tree (= no
circular pathes allowed) first, which you then can traverse recursively.

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I think I know how to do that!  Time will tell!

On 12/29/2016 12:01 PM, Parkinbot wrote: