[Problem] Draft: Sometimes face/sketch exports to flattened SVG or DXF incorrectly

[FreeCAD-Bug-Importer]

Issue imported from https://tracker.freecad.org/view.php?id=4133

• Reporter: bug_reporter_00342
• Date submitted: 9/17/2019

Original report text

I've been seeing this bug very occasionally I believe since 0.16, seemingly at random. Trying to export a particular sketch as a flattened svg or dxf truly flattens the constituent paths such that they lie on top of each other when they should not. It may be that the paths are being projected along the wrong (90deg) axis to produce the exported vector image.
Trying to export a clone or facebinder of the relevant sketch then exporting produces the same results.

Additional information

OS: Ubuntu 18.04.3 LTS (ubuntu:GNOME/ubuntu)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.
Build type: Release
Python version: 3.6.8
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)

Steps to reproduce

Open attached FCStd file, cant_export_Sketch002.zip

Try to export Sketch002 as Flattened SVG or DXF. View exported file in Inkscape or similar, visually compare to original sketch.

For reference, Sketch001 exports fine. Rotating the body of Sketch002 by 90deg to lie parallel to the plane of Sketch001 does not solve the issue.

Tried in 0.17, 0.18, and 0.19 Daily with the same results.

Discussion from Mantis ticket

Comment by bug_reporter_00342 2019-09-17 17:21

Workaround is to pad the sketch, export the pad as a STEP file, open the STEP file in a new FreeCAD document, recreate the original sketch by tracing out the face using external geometry, then export the new sketch as SVG or DXF.

This workaround does not support sketches that cannot currently be padded, such as those which would produce multiple solids.

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Comment by Kunda1 2019-09-19 02:53

Forum thread: https://forum.freecadweb.org/viewtopic.php?f=3&t=39441

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Comment by Kunda1 2019-09-27 10:48

Apparently, similiar discussion at https://forum.freecadweb.org/viewtopic.php?f=3&t=33708

[Roy-043]

See also: #11224

[Roy-043]

#11890 has fixed the issue for the C++ DXF exporter.
Let's leave this open for the legacy DXF exporter and SVG export.

[jnweiger]

Here is a potential fix for the SVG exporter: #13652

For anybody who wants to try this with 0.21.2, here is a backport #13658
fix-export-svg-direction-0212-diff.zip