This is the example from the docs:

CubePoints = [
[  0,  0,  0 ],  //0
[ 10,  0,  0 ],  //1
[ 10,  7,  0 ],  //2
[  0,  7,  0 ],  //3
[  0,  0,  5 ],  //4
[ 10,  0,  5 ],  //5
[ 10,  7,  5 ],  //6
[  0,  7,  5 ]]; //7

CubeFaces = [
[0,1,2,3],  // bottom
[4,5,1,0],  // front
[7,6,5,4],  // top
[5,6,2,1],  // right
[6,7,3,2],  // back
[7,4,0,3]]; // left

The points are the 8 corner points you've already determined; what you have
to do now is to tell OpenSCAD how those go together to make faces. So the
bottom face is made up of points 0, 1, 2 and 3 (it closes the loop
implicitly), the top is 7, 6, 5 and 4, and so on. The tricky thing is that
you have to maintain a consistent direction as you specify the points that
make up a face. You have to go consistently either clockwise or
counterclockwise (from the outside looking in). You can't go back and
forth. That's why the points in CubeFaces are ordered the way they are.

On Mon, Sep 6, 2021 at 6:41 PM Gene Heskett gheskett@shentel.net wrote:

By the way, if you just drop your measured points into CubePoints, it will
probably work.

On Mon, Sep 6, 2021 at 7:46 PM Father Horton fatherhorton@gmail.com wrote:

On Monday 06 September 2021 20:46:16 Father Horton wrote:

It finally sank in that the cw/ccw is per face, not around the box. so
now I get that. But I don't need a top or bottom.  So how do I reorder
to leave out the top and bottom, all I want are the sides which will
then be built up on the inside to do the job, effectively winding up on
the printer as a half box with a big difference removing about half the
box. These measurements only serve to define the outside dimensions of
the part I'm actually building. And it needs a 30 degree angle on the
edges of the ends cut off. That can be done later so its not an instant
problem ATM.

I'll see if some sleep helps.

Thank you.

wrote:

Cheers, Gene Heskett

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.

• Louis D. Brandeis
  Genes Web page http://geneslinuxbox.net:6309/gene

On Monday 06 September 2021 20:53:53 Father Horton wrote:

I tried to outsmart myself by doing a /2 on the xy stuff so it would be
self centering on the build plate by using value, -value in the arrays.
I think that may be contributing to my confusion.

Thanks Father Horton.

Cheers, Gene Heskett

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.

• Louis D. Brandeis
  Genes Web page http://geneslinuxbox.net:6309/gene

A picture is worth a thousand words.

Sounds like you want outside thickness.

Similar to this triangular example (lower corrected one) from:

https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#Mis-ordered_faces

polyhedron

(points = [

        [0, -10, 60], [0, 10, 60], [0, 10, 0], [0, -10, 0], [60, -10, 60], [60, 10, 60], 

        [10, -10, 50], [10, 10, 50], [10, 10, 30], [10, -10, 30], [30, -10, 50], [30, 10, 50]

        ], 

 faces = [

         [0,3,2],  [0,2,1],  [4,0,5],  [5,0,1],  [5,2,4],  [4,2,3],

              [6,8,9],  [6,7,8],  [6,10,11],[6,11,7], [10,8,11],

         [10,9,8], [3,0,9],  [9,0,6],  [10,6, 0],[0,4,10],

              [3,9,10], [3,10,4], [1,7,11], [1,11,5], [1,8,7],  

              [2,8,1],  [8,2,11], [5,11,2]

         ]

 );

--
This email has been checked for viruses by AVG.
https://www.avg.com

It is not clear to me why you need a polyhedron with missing faces but to
get it just drop the faces you don't want from the list of faces of
the polyhedron. However, it should be clear that the incomplete polyhedron,
which doesn't enclose a volume, will not be rendered (F6) and so no STL is
possible to be produced although OpenSCAD is able to produce the expected
image in a preview (F5).

Note also that a cube without the top face unioned with a similar cube
positioned on top of it but without its bottom face will not be assembled
as a valid object. Each polyhedron in a boolean operation (union,
intersection or difference) should be valid by itself, that is, enclose a
volume.

For each polyhedron you define, check it with View/Thrown Together. Faces
with inconsistent windings will be shown with different colors.

Em ter., 7 de set. de 2021 às 03:25, Gene Heskett gheskett@shentel.net
escreveu:

On Monday 06 September 2021 22:31:22 Gene Heskett wrote:

OK, I got that box, all yellow so I assume its right. But its now a solid
box. How do I remove the top and bottom faces so I can work inside
this "bounding box"

Got that too, but the inside is all magenta. Is that fixable or
ignorable? In any event I now have the "bounding box"

I then made a union between 2 polyhedrons, one inside the other, but it
didn't fill the gap between them, how is that done?

And when I meant to simplicate it by doing addition and subtraction
between 2 valid vars in the list of points, I got told I cannot do that.

Do I have to predefine every var I use in a point list in a separate
varname=value; or varname=[var1-var2]/2; statement?  This will quickly
take the define statements to different places in the file requiring
huge amounts of scrolling back and forth to keep track of the point and
face lists.

I note the docs do not show vars, just integer numbers. But they appear
to work as long as they are predefned first.

Progress, slowly as the rules begin to become more obvious as I stumble
over the violations.

Thank you.

Cheers, Gene Heskett

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.

• Louis D. Brandeis
  Genes Web page http://geneslinuxbox.net:6309/gene

On 07/09/2021 08:54, Ronaldo Persiano wrote:

I'm still not sure what it looks like to you, but to me, from the above
description, it would be two polygons (not polyhedron) , one inside the
other, extruded, and top and bottom chopped off however you want by
differences.  That will give a solid, and you can add features/whatever,
as you wish.

You can't take a face of the polyhedron to get an open box. It is not a
manifold solid because the walls would infinitely thin. If it is an
irregular shape that can't be linear_extruded then make two solid
polyhedra, one for the outside and one for the inside and subtract them.

You don't need variables for each point in the polyhedra, they can be any
expression.

On Tue, 7 Sept 2021 at 12:35, Ray West raywest@raywest.com wrote: