With imported objects, I spend a lot of time displaying various cubes with
% to find the exact position of various planes in the objects, so I can
offset them properly. Unfortunately, there seems to be no way to ask the
system for this information.

On Thu, 11 Jul 2019, 11:31 bboett, bboett@gmail.com wrote:

Right - OpenSCAD can't do this for you.

The "trick", really, is to design all your parts around a convenient
origin and then translate them to the assembled position.  It seems most
people's intuition is to model the part in the assembled position and
then try to move it back to a convenient origin for printing (or
whatever else).

I'm sure some will debate this being a better way, but it's much more
obviously the best way if you get to a point where you're reusing models
that you created.  Having a convenient origin makes this much more
practical, for a lot of reasons.

Joe

On 7/11/19 10:34 AM, A. Craig West wrote:

Generally I do the import with offsets to zero it to origin in a module,
then use offsets to position the module appropriately

On Thu, 11 Jul 2019, 11:40 Joe Francis, joe@lostapathy.com wrote:

bboett wrote

Repetier Host will lay it flat for you. Earier versions required the use of
the "Lay Flat" icon in the Object Placement tab, but in trying it just now,
a test cube, translated to 10,10,10 actually does drop to the bed when
loaded. Then, you can move it to the origin (0,0) of your bed, and export it
(Export icon, box with exiting arrow).  My Repetier Host is V2.1.3

But a better way to import STL files and position them is to use a rather
nifty little python script written by Jamie Bainbridge, called stldim.py,
modified by me.. His original script can be found at:

https://www.reddit.com/r/3Dprinting/comments/7ehlfc/python_script_to_find_stl_dimensions/

I have modified it to produce a OpenSCAD translate() statements to position
any imported STL (or any other object, for that matter) in any one of the
four quadrants, or the center of X,Y, and Z.

See
http://forum.openscad.org/Getting-dimensions-of-imported-shape-tt24237.html#a26496
for my modified script and instructions for use.

I see that many folks have asked for a way to find and use a bounding box in
OpenSCAD, and I wonder if it will ever be implemented. It would be very
handy, and its use could be implemented as just information in the console,
or used directly in something that might be called "absolute_translate().

--
Sent from: http://forum.openscad.org/

On 7/11/2019 11:00 AM, lar3ry wrote:

Perversely, I don't think OpenSCAD itself knows the bounding box,
because it doesn't do the geometry work.  The output from OpenSCAD
execution is a list of objects, transformations, and boolean operations,
and OpenCSG and CGAL are the ones that do the geometry work.

If you look at Design > Display CSG Tree, I think that's the output from
the execution phase.

Maybe, after rendering, there could be a view of that tree that includes
bounding box information.  You couldn't use it as part of the execution
of the program, but you could copy and paste it.

relativity.scad library does alignments

On 7/11/19, Jordan Brown openscad@jordan.maileater.net wrote:

On 7/11/2019 2:01 PM, GZ wrote:

Aligning objects a priori is not hard.  What's not possible is taking
some arbitrary object and determining its geometry after it's been
constructed.

That is:

cylinder(h=10, d=2);
translate([-1,-1,10]) cube(2);

will more or less reliably give you a cube atop a cylinder.  However, if
you then

module foo() {
	rotate([45,0,0]) {
		cylinder(h=10, d=2);
		translate([-1,-1,10]) cube(2);
	}
}

there's no way to perch something on top of the resulting foo() without
doing math.

I'm too lazy right now to do the math, but experimentation says it's at
about [ 0, -7.8, 9.2 ].  There's no way to get that value out of
OpenSCAD, or to get the foo's bounding box.

Relativity helps you to construct a model with specified alignment, but
does it at the front of the pipeline.  You can't give it an arbitrary
existing object like foo() above and expect it to be able to align
additional objects relative to it.  Relativity can only work because it
knows the geometry of the objects it's putting together.

lostapathy wrote

This also has the added benefit of being more modular. It's easier to reuse
components if they have a sensible origin. Say, for example, that I model a
bolt. I then put it at the origin, wigh the XY plane just below the head,
oriented along the Z. This makes a lot more sense when I want to use that
bolt in some other design.

--
Sent from: http://forum.openscad.org/

Yes make the origin the most useful point but if there are other points of
interest, for example screw holes, than I make a module that moves its
children there and use it to make the holes both in the object, and what it
mounts to and place the screws. So I never need to calculate positions. It
is simply a combination of modules. E.g.

motor_position() {
motor();
motor_screw_positions()
screw(motor_screw(), 10);
}

Similarly I have functions to get the important dimensions of each object,
so I know its bounding box allowing me to place it in an assembly and
design other things round it.

The rule is never specify anything twice. Always factor it into a function,
module, or variable and define it once and re-use it.

On Fri, 12 Jul 2019 at 07:45, Troberg troberg.anders@gmail.com wrote:

On 2019-07-11 20:00, lar3ry wrote:

It is a handy feature, standard in AngelCAD, where any shape can return
a bounding box
https://arnholm.github.io/angelcad-docs/docs/classshape.html#a9511e310496d8d70c26cf0c4b59b0200
https://arnholm.github.io/angelcad-docs/docs/classboundingbox.html

Carsten Arnholm

Bounding box isn't implemented in OpenSCAD because geometry is not
calculated for the preview, so it isn't available until you do F6. Not only
that but all expressions are evaluated before the geometry is created. That
is why you can never query the geometry, you can only specify it.

On Fri, 12 Jul 2019 at 09:47, arnholm@arnholm.org wrote: