This is rather critical. It would be very useful to be able to print a
1:1 or a known scale "object" to real dimensions.  To take a simple but
probably common example, making a case for a Raspberry Pi.  After all
the work to get close to such a design, it would be very helpful to be
able to print orthographic versions of the  model to test the "fit" of
the model to the real thing. It has been of considerable irritation that
few graphics programs (apart from Inkscape) bother to keep their
rendering of objects to some real world reference.  I was actually very
surprised when I found out that in openSCAD a dimension of 1 actually
was a reliable 1mm.  Amazing!! This was quite unexpected as I have
become used to so many '86 programs not bothering about the real world.
Given that the resolution of a printer is available from the drivers,
any program should be able to render a pretty close printout of the
object, to within fractions of a mm. If it can be done for a 3D printer,
why not a 2 printer???  Not everyone has the materials, or the time
(especially) to print a plastic 3-D model to just see if it fits.  So a
hardcopy printout with sub-mm accuracy would be very handy.  Given the
openSCAD has buttons to produce orthographic views, why not make it
possible to print 1:1 or at least exact scale versions of those
views/models.

It would be better if this was built into openSCAD, rather than
someone's "late program-atical add on".  Apologies to MichaelAtOz and
others who may have spent many hours reverse engineering this
distortion. Your skills are far greater than mine.

Enough of my ramblings what do others think?

Rob

On 04/12/16 13:11, MichaelAtOz wrote:

On 12/04/2016 08:59 AM, Rob Ward wrote:

Strictly speaking that is not true. It's currently some kind
of common assumption for STL tool chains as STL does not have
any means to store any unit information.

SVG and AMF for example have a way to specify units and this
is currently hard coded to mm which is not the best solution.
There is already a feature request on github that will change
this to be an option when exporting files. At this point it
would be perfectly sensible again to design in OpenSCAD with
an unit of 1 meter and export that correctly to AMF.

It should be possible to print SVG directly instead of
converting to bitmap, maybe simply via a web browser?
I never tried that myself but some bug reports regarding SVG
output seem to imply people did that.

I'm not even aware anybody created a feature request for
this until now, so why would someone implement it if there's
no need? There's a huge backlog of stuff that someone actually
asked for.
If it turns out to be a useful feature, it makes sense to
create a feature request for this. Looking at the technical
side, I suspect it might be much more difficult to implement
than it seems as the current PNG export is pretty much just
a screenshot which leads to all the effects MichaelAtOz
found.
Realistically it might be much faster to find a program
that correctly prints SVGs (and maybe even document that
in the manual), especially with the added bonus that we
don't need to care about resolution as we'd need to do
for PNG output.

ciao,
Torsten.

MichaelAtOz wrote

I think you will need to find the correct value of $vpd to get it. I would
guess a value, print an image with the scales, measure the printed scales
and change $vpd accordingly. It will possibly depend on your graphic card
resolution.

--
View this message in context: http://forum.openscad.org/Anyone-know-how-to-export-an-image-to-scale-1-1-tp19454p19460.html
Sent from the OpenSCAD mailing list archive at Nabble.com.

That sounds much better than my idea.  Producing an SVG that allows
further editing of the underlying shape would be excellent as it would
also allow for illustrative shading etc as well as the obvious bonus of
annotations etc  To some extent, the options to show "Wire Frames"  or
"Edges", and align to orthographic views, could mean that a lot of the
information on how to do this exists (NB naive programmer being
optimistic).  Flattening that to an SVG and letting InkScape take care
of the final printout and printer resolutions etc would be a very good
option. This image could be used to export .png or .jpg etc

Long, long ago, there once was a program called !Draw and it could do
powerful 2D CAD, and it could be set to mm and print sub mm accuracy on
any printer that had standard drivers.  This was Acorn c.1990 and on a
RISC PC with an ARM chip.  Swapping to Linux 4 years ago and discovering
many new packages (to me), both InkScape and openSCAD with their "no
nonsense" approach to rendering reality was really refreshing.  Hence my
surprise, pleasure, that 1 =1mm.  Watching students over many years
trying to make MS Paint do stuff used to bring tears to my eyes.

We can import SVG, why not export it as well?

Rob

On 04/12/16 22:40, Torsten Paul wrote:

--

Rob Ward
Lake Tyers Beach, 3909
Lake Tyers Beach Website http://www.laketyersbeach.net.au
XP to XUbuntu http://www.laketyersbeach.net.au/XP2XU.html

You can export SVG as long as your top level model is 2D. You can use
projection() to get cross sections of 3D objects.

On 4 December 2016 at 22:04, Rob Ward rl.ward@bigpond.com wrote: