Hi, Welcome to the forum.

OpenSCAD is unitless.

When you translate it to some output device is where an assumption is made
what 1 is equal to.

Many 3D printers assume 1=1mm, but there are also plenty of designs in
inches, which means when you want to print them you need to scale it.

I'm a metric thinker, so I like to design assuming 1=1mm.

1inch=25.4mm (as I assume you know) so it is just a matter of scaling
up/down depending.

I suppose it comes down to how hard it may be to convert your scripts,
and/or how your head hurts thinking in other units of measure.

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For AMF export, the unit of measurement is 1 millimeter. That's hard coded.

There may be other cases of import or export where we support units of
measurement, but I'm not aware of them. I'm pretty sure that our STL, DXF
and SVG support is unitless.

On 3 December 2015 at 20:54, MichaelAtOz oz.at.michael@gmail.com wrote:

mm_per_inch is already defined in <MCAD/constants.scad> and
<MCAD/math.scad>.
Also, math.scad defines deg(x) for converting x radians to degrees.

On 3 December 2015 at 21:54, Neon22 mschafer@wireframe.biz wrote:

Surely this is just a case of adopting a convention and making it the case,
it should only impact exporters and importers.

If the community decided that the dimensional value 1.0 inside openscad
reffered to 1mm then all it needs is documentation to that effect.

Having it unitless only creates confusion, and opens the door for models to
be missinterpreted during exchange.

It would allow importers and exporters to work in real world units, for
example import dxf and export amf would work correctly and have the right
units

On Fri, Dec 4, 2015, 11:04 doug moen doug@moens.org wrote:

That doesn't really work for a lot of applications. Consider a railway
model. It's drawn to full scale (about 21m long) taken from reference
drawings. It might be printed in a range of different model scales.

You might naïvely argue that the scale is then either "1:1 in mm" or
"whatever scale you wanted in mm" but actually its neither. The inputs to
the model consist of both elements scaled at 1:1 and elements scaled at
1:whatever because the wall thickness for example is dependant upon the
final result while the majority of the detail is based on the 1:1
dimensions.

Yes the final result might be at 1:1mm but the notion that its some kind
of generic unit throughout OpenSCAD just wouldn't work.

Other examples like screws have similar behaviour. You can elongate a
screw but generally the thread doesn't change dimensions. Often if you
make it bigger the same is true.

Alan

What I have done in OpenSCAD and similar languages like Povray is this:

Inch = 25.4
Foot = (12 * Inch)
and so on

It doesn't change anything, but you can then use the units that make sense,
as long as the software can deal with the scale.  In Povray I worked on a
huge animation project where none of the modelers could agree on what a
unit should be, so I made a define that had every linear unit I could think
of from Light_Year to Micron  Cubits, Furlongs, all were in there.

On Fri, Dec 4, 2015 at 9:17 AM, fractorr fractorr@gmail.com wrote:

--
K1FZY (WA4TPW) SK  9/29/37-4/13/15

Tim Hawkins wrote

Yes the community, not just the OpenSCAD, but the larger 3D printing/rapid
prototyping community, have decided and adopted a convention and
documentation
to that effect: the programs and data files shall be unit-less.

If you can convince the world to change the STL definition to adopt a
physical
unit, you are welcome to come back here to preach it for OpenSCAD.

https://wps3dprinter.wordpress.com/designing/stl-units/

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