Hello,

I have a simple polyhedron and I'm trying to attach a cube to it. My code is
below.

The preview looks like this:
http://forum.openscad.org/file/n16132/img1.png

The render looks like this:
http://forum.openscad.org/file/n16132/img2.png

If I remove the cube, it renders fine:
http://forum.openscad.org/file/n16132/img3.png

I've read a bunch of posts regarding this subject on the OpenSCAD forums and
a few other places and I can't seem to figure out why my object is not
rendering correctly.

If anyone can shed some light, I'd really appreciate it.

Here is my code:

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Hello

You must connect the top vertices of the top triangles. If you check the
part in wireframe mode "F11" you will see what I mean.

jpmendes

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Hey

Check this.

Code:

$fn = 180;

size = 34;

side_a = size * sin(45);
side_b = size * cos(45);
side_c = size * tan(45);
tri_top_0 = [0,0,0];
tri_top_1 = [side_b,0,0];
tri_top_2 = [0,-side_a,0];
tri_bot_3 = [0,0,size];
tri_bot_4 = [side_b,0,size];
tri_bot_5 = [0,-side_a,size];

show_mount_plate = true;

mount_plate_thickness = 5;

union() {
polyhedron(
points=[
tri_top_0, tri_top_1, tri_top_2,
tri_bot_3, tri_bot_4, tri_bot_5,
],
// faces=[ [0,1,2], [3,4,5], [0,1,4,3], [1,2,5,4], [2,0,3,5] ]
faces=[ [1,0,2], [3,4,5], [1,2,5,4], [0,3,5,2] , [0,1,4,3 ] ]
);

if (show_mount_plate == true) {
    translate([0,-side_b,0])
        rotate([0,0,-45])
            cube([mount_plate_thickness, size, size]); 
}

}

jpmendes

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Thanks for the help jpmendes and peter!

I was just reading about the "Point ordering for faces" in  the manual
https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#polyhedron
and it looks like my problem was with the order of points in the bottom
triangle going counter-clockwise instead of clockwise.

Thanks so much for the tips!

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Hey

In fact it is sufficient to change the order of the points of the bottom
triangle only:

faces=[ [1,0,2], [4,3,5], [0,1,4,3], [1,2,5,4], [2,0,3,5] ] );

Can anybody explain why?

Thanks

jpmendes

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Ok, I read the manual.

However I can't understand why this have to be this way. I do not imagine me
spending a lot of time making a complex polyhedron from points and having to
care about the order of points for each face.
I think that the language should infer the correct order and rearrange the
points order internally if necessary to avoid crashing or the type of issues
above.
As a minimum, an error message should be echoed reporting the faces with
problems.

jpmendes

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