<kintel>
greyltc At the moment, I would extrude my 2D object my a minuscule amount using linear_extrude()
<kintel>
guso78 Not sure if you're still up, but I think the typical answer is to project your polygons into 2D space by projecting onto its own plane, then use 2D polygon-in-polygon
<greyltc>
kintel: extruding the source objects leaves artifacts in the geometry
<greyltc>
is it a bug in the hull() function that doesn't work correctly on 2d children?
<kintel>
Not a bug: You cannot apply a 3D transformation to a 2D object, since the object lives in 2D space, and we don't yet support "2D in 3D" geometries
<greyltc>
generates exactly the geometry that I expected my hull() example above to
<greyltc>
how can there be code that runs when a circle is defined with r=, but not d=?
<greyltc>
that's nuts!
<greyltc>
I can't imagine trying to debug that...
<greyltc>
thank you for pointing me to skin() btw!
<greyltc>
it seems to work great with circles, which is all I need it for. I expect it's gonna have some issues with lofting through shapes other than circles though
<kintel>
greyltc It's because the "circle()" used in that example isn't OpenSCAD's circle() module
<kintel>
..it's a user-defined circle() _function_ returning coordinates describing a circle
<kintel>
OpenSCAD has an ..interesting feature: modules and functions have different namespaces and it's always clear from the context if we're going to look up a function vs. module
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<guso78k>
kintel: I have also considered projecting the 3D polygons into 2D space, but its not as simple as OpenSCAD project function to simple drop the Z coordinate, because the polygons could be oriented normal to XY plane , so its might be an time expensive operation.
<guso78k>
I;d like to be very effective because I have to apply this op many times. Do you have any links how to project a 3D polygon into 2D space ? its not unique because there is still a rotary freedom involved.
<guso78k>
But yes once I have them fast in 2D space, shown 2D algorithms might be very interesting
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<knielsen>
guso78k: just curious, if a polygon is normal to the XY plane, how do you want it to be projected to 2D? Just remove it or what?
<guso78k>
if my polygons are normal to XY plane i would need to rotate them in a way (by 90 deg) so their area is unchanged ...
<knielsen>
aha, right, so you need to somehow find the right plane to project to, makes sense
<guso78k>
i think they could be rotated by make a cross product with a special 3d vector. i just dont know yet exactly where it needs to point at ...
<knielsen>
I think it's something like: take two perpendicular unit vectors in the plane of the polygon, along with their cross-product, and build a 3x3 matrix from those 3 vectors. And then multiply with the inverse of that matrix to rotate into the XY plane
<guso78k>
without understanding, whats going on and why, it sounds like a quite concrete strategy. suppose the 3 vectors beeing vertically itself , have to be aligned horizontally next to each other. what's their order ?
<guso78k>
can it happen, that matrix inversion is not possible due to 0-determinant ? suppose this is when the polygon is parallel to XY already
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<guso78k>
ahh now i understand, the order is xvec-yvec-zvec wherease zvec is xvec x yvec and you basically just "undo" the transformation into the orientation where the polygon is right at the start
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<knielsen>
yes
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<Pringle>
Hello, Im working on my first 3D modeling project since college and really liked the idea of scripting as a modeler. I was hoping to get someones expertise on a small idea for my first print in my new printer.
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<Scopeuk>
Pringle if your trying to get started with open scad the tutorial is pretty good, otherwise giving it a go and asking specific questions is probably the way to go
<Scopeuk>
people will happily talk about designs or models here if you would like to
<Pringle>
Awesome thanks for the responses. Mainly wanted to check to see if this chat was active. Once I get going ill see what questions arise. Thank you!
<Scopeuk>
it is active here but it can be quiet, it usually picks up evenings for European time zones, the amount of traffic varies but people are lurking
<Pringle>
(y)
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<InPhase>
Pringle: A common event is, "I was trying to find a good way to express this in OpenSCAD: *shows code and example of desired result*" Then a hoard of people race to compete for the best way to express that. ;)
<Pringle>
```test```
<Pringle>
Is there a wait to format the code in chat?
<peepsalot>
pastebin
<Pringle>
sry not sure what that means
<Pringle>
Well here goes nothin - Im trying to make a truncated octohedron with some faces solid and some open. At this point it doesnt matter which faces are which. To make this shape Ive boiled it down to the intersection of two common shapes; a octahedron, and a cube. This is a two parter question. First, how do I rotate the cube 45*? Second, when I put
<Pringle>
the two shape objects through the intersection function I only get the top half, what happened to the bottom? Thanks!!!
<InPhase>
Pringle: You should put that at https://bpa.st
<peepsalot>
a pastebin is a website (there are many, e.g. https://bpa.st/ ) that provides a service where you paste text into it and it creates a link you can share
<InPhase>
Code formatting on IRC is terrible, and hard to copy and paste back out. So it's a taboo IRC thing to paste code directly (we forgive you, you're new). So pastebin sites like bpa.st are used.
<InPhase>
Pringle: As for the disappearing side, that's going to be because some of your faces have the wrong winding order.
<InPhase>
Pringle: That'll be in the manual under the right-hand rule.
<Pringle>
So the example just below showing a pyramid is wrong?
<InPhase>
Pringle: An example of achieving this without struggling with polyhedron is this: https://bpa.st/HEVQ
<InPhase>
I'm using "render" here just because preview is going a little wonky on this on some conditions, and this is a small simple shape, so tossing in the render() call gives preview something clean to work with and it's plenty fast enough because it's simple.
<Pringle>
ok thank you for the help, and sorry for the elementary questions
<InPhase>
Pringle: Note that the inner part with the linear_extrude on the squares violates the overlap rule, which should pretty much ALWAYS be followed, but it works here because it's aligned exactly on the z axis.
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<Pringle>
ok if i rotate the cube 45, I dont quite get what i was looking for. I guess i need to read a bit more on what this render does.
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<Pringle>
InPhase All I had to do was make the cube a bit bigger to get the shape I was after. Thank you for this. Im wondering how I can remove some of the faces now so I can access the inside of this shape?
<InPhase>
Pringle: Can you clarify what you mean by access the inside?
<InPhase>
Pringle: Do you mean, hollow it out?
<InPhase>
Like a bucket/jar?
<InPhase>
Pringle: That involves making two copies, one bigger than the other by the desired wall width, and doing a difference operation. The best way to do that is to put the shape into a module with a parameter for the extra width, and then wiggle that extra width amount into all the numbers for the shape at the right spots. Then you have one copy of the shape, and you difference the module with and without
<InPhase>
the extra width.
<InPhase>
And you'll have to add a little special bit to put the opening wherever you want it.
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<Pringle>
InPhase
<InPhase>
Pringle
<Pringle>
InPhase Sorry I got disconnected and didnt realize until after I @'d you.
<Pringle>
So heres what Ive added. Still not sure how to remove the faces im wanting. https://bpa.st/B6YA
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<InPhase>
Pringle: You want to avoid reusing code, so like this: https://bpa.st/7FYQ
<InPhase>
I mean, avoid repeating code.
<InPhase>
I have no idea if that matches your mental image, but something like that.
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<Pringle93>
idk what happened to my user...either way. you are a wizard! honestly very impressive ha. This is exactly what im looking for.
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<InPhase>
:)
<InPhase>
Pringle: There are a small number of tricks like this to learn, and once you see a few examples like this, you'll be popping out the same sort of thing. :)
<Pringle>
InPhase Its honestly a lot of fun, just a lot to learn at first :) I was able to get the rest of the squares, how would I get the hexagonal faces? Heres what Ive tried so far, but feel like im just guessing on locations/rotations. https://bpa.st/6PPQ
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<InPhase>
Pringle: Well, there are a few approaches to that sort of thing. One is to do the math for where those hexagonal faces are, and sort it out that way! Another is to rethink the whole thing as a constructive problem, and build the wireframe of your object instead of trying to hollow it out. This would require some math too. A third is to try to do a half-math approach and reuse your existing shape,