Ticket #3420 - SVG imports from inkscape lead to wrong dimensions

[Kunda1]

issue #3420 - SVG imports from inkscape lead to wrong dimensions
Bug was first isolated thanks to the german FreeCAD contingent in https://forum.freecadweb.org/viewtopic.php?f=13&t=27344

With the change from 0.91 to 0.92 inkscape devs changed the conversion factor of userunit (uu) and mm. Pre-0.92 it was 1uu=1 inch/90 and starting from 0.92 it is 1 uu=1inch/96. This was necessary to meet the actual recommendations/rules of svg-standard and css. See article in inkscapewiki for further reading.

When a user creates a file in inkscape with absolute dimensions (mm) and saves it, then imports it into FC, bodies in Freecad come out with too large dimensions. For example - a 100mm square will be 106,66mm in FC now (100 x 96/90).

Example SVGs are available in the ticket

[Kunda1]

Will there be a need to make an import pop-up asking if the user wants pre-Inkscape0.92 or post-Inkscape0.92 compatibility?

[PrzemoF]

Maybe we could use the version stored in the actual SVG file?

Code: Select all

inkscape:version="0.92.4 (5da689c313, 2019-01-14)"

[chrisb]

Will there be a need to make an import pop-up asking if the user wants pre-Inkscape0.92 or post-Inkscape0.92 compatibility?

No, I don't think so. It is all going to the newer versions, in FreeCAD as well as in Inkscape. When 0.19 becomes stable even more people use newer inkscapes, probably 1.0.

[Kunda1]

Maybe we could use the version stored in the actual SVG file?

Code: Select all

inkscape:version="0.92.4 (5da689c313, 2019-01-14)"

Hey @PrzemoF, would you mind elaborating how that could be useful?

[PrzemoF]

I hope I don't miss something obvious
- in inkscape up to Pre-0.92 it was 1 uu=1 inch/90
- in inkscape starting from 0.92 it is 1 uu=1 inch/96
- SVG file created by inkscape contains a line like this:

Code: Select all

inkscape:version="0.92.4 (5da689c313, 2019-01-14)"

So by checking the version of inkscape that saved the actual SVG file you can tell what should the conversion factor.

[openBrain]

Given that the second (96 DPI) should be the standard.
Actually maybe a better algorithm is "SVG is 96 DPI except for Inkscape < 0.92 where it's 90 DPI".
Hope this is the current behavior.

[Kunda1]

Hey @wandererfan, could you weigh in on this? How are we evaluating SVG's currently ?

[wandererfan]

Hey @wandererfan, could you weigh in on this? How are we evaluating SVG's currently ?

Geometry imports are done by Draft.importSVG.py and it has 90 ppi hard coded in a number of places.

Drawing and TD don't seem to consider ppi at all, just user units.

[Kunda1]

Looks like it's in the getsize() function: https://github.com/FreeCAD/FreeCAD/blob ... VG.py#L263