/"I don't understand how you can discuss this for so long. It is so simple."/

In addition to Jordan’s thorough reply, I’m sure you’d agree that most tasks
are ‘simple’ once you know how. Another recent example would be "How to snap
the OpenSCAD view at right angles to the XY plane?"

But I’m a novice, having installed InkSpace on Tuesday. And I’d still regard
myself as a novice with OpenSCAD too, installed 10 weeks ago. So yes, I’m
sure I’m making heavy weather of tasks that experienced users find obvious.

As you seem to have missed it, here’s the objective I described in my
opening post:
/"...getting precise measurements from a photo into OpenSCAD when accurate
physical measurements with ruler and calipers are difficult."/

It also seems you may not have read my opening post in the QCAD forum, which
I referenced in that same post:
/"Just installed QCAD which I'm hoping will help me get more accurate
measurements into OpenSCAD."/

That quickly led to recommendations on how to do so in Inkspace. My focus on
using its Trace Bitmap facility was probably naive. I now hope to learn some
of its scores of drawing tools and your video will be useful, thanks.
Although even better if you’d drawn the image I uploaded instead of that
random scribble! And perhaps added an audio or text narrative on what you
did at each step, and why?

Terry

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No problem, D, it's all good learning for me!

My main handicap (apart from the unfortunate restriction of a mere 24 hours
daily) is self-made. I'm impatient to get practical results but at the same
time keen to learn methodically ;-)

Terry

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It probably didn't help that details were in two separate threads. Perhaps I
should have duplicated after all  ;-)

In summary this is a small practical project, my first design attempt, to
print a replacement plug cover. But primarily as a learning exercise. My
approach has varied, following different suggestions, but currently I aim to
linearly extrude an accurately traced or drawn profile to a height (Z) of
about 21mm.

Actually each of the three surfaces has a slightly different width (Y), as
well as length (X) and also tapers a bit. But I'll tackle those
complications later, together with the bolt/screw hole in the second surface
and the cable hole in the third. Right now I'm focusing just on the cover.
Call it stage #1 of this learning exercise!

Although I know that some scaling can be done in the slicer, I'd like to get
it right before that.

1. Overhead photo with iPhone.
2. Edit in my image editor PaintShop Pro (PSP), removing all but the profile
   due for extrusion
3. Import into Inkspace (which I installed only two days ago) and trace or
   draw what I gather is a 'vector path'.
4. Export that to SVG. (I have not yet pursued the DXF alternative.)
5. Import to OpenSCAD and save to STL
6. Slice in Cura slicing and save as gcode.

See my screenshot yesterday of the SVG imported to OpenSCAD, with the code

linear_extrude(400)
import("C:/Users/terry/Dropbox/3D
Printer/PROJECTS/PlugCover/EditedPhoto-Brightness550.svg");

Here also is a four-screenshot composite for info.

http://forum.openscad.org/file/t3184/FourScreenshots50.jpg

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Thanks, there was a tiny improvement. Yet to test this as a print. But
plainly manual drawing will be better when I get around to it.

http://forum.openscad.org/file/t3184/OffsetTest.jpg

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Is the idea that you make a plug cover (whatever that may be? I've only
seen one photo) or is the idea to precisely copy an existing item
(definition of 'precisely' may vary). The item you are trying to
replicate probably solves a problem, but it does not necessarily solve
it in the best way. If the idea is to 3d print it, on the diy type fdm
printer, then perhaps you need to tweak the design to give a better
result. I think that possibly you've leapt into inkscape, tracing
images, etc, whereas the problem you are trying to solve, (i.e. make a
cover) may need none of that. You've mentioned it is difficult to
measure it. Basic measuring will do, six inch ruler, graph paper maybe
better still a cheap digital caliper an $8 (or a $3 vernier caliper
batteries not included 😉)  will do for this sort of task, but even 
with none of those you can get to the right size by trial and error
methods and a good eye. If you have access to a flat bed scanner, then
that will give less distortion compared to a camera. If you have a
camera, then take some photos of known sized objects, at known focal
distances etc, so the lens can sort of be calibrated. (you could take a
photo of a credit card, process it/import to openscad, print it,
applying scaling so it is the same size as original, then it would give
a good starting point wrt camera/processing errors.) I have the feeling
you are battling with too many unknowns - inkscape, openscad, camera
distortion etc. Of course, if it was easy, everyone would be doing it.

Making it simple, if you want to make a plug cover, work from the plug
you are trying to cover. If you want to accurately copy an existing plug
cover, then start by accurately copying something simpler, so you can
more easily eliminate errors. (lego brick, say?) In that way your
learning will be more able to focus on a particular aspect, instead of
wondering down disparate paths.

Best wishes,

Ray

Thanks, I’ll try those code changes. Although I probably won’t use minkowski
from now on for this part.

Re image size, would most subscribers prefer links instead, which would be
just as easy for me?

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