Inkscape accuracy?

[johnse]

My experiments in this linked thread were all comparing outputs from Illustrator and Inkscape, rather than imports, but I think the same info applies:

The Great Dimensions Debate

I’ve seen a number of posts talking about 20x12 artboards vs. 5:3 artboard aspect ratios and how the GFUI deals with them. I’ve also seen discussions about differences in Inkscape DPI resolutions, and assumptions that GFUI defaults to 96 DPI. Yet I’d noticed during my experiments with Illustrator that using the Glowforge-endorsed “Save As…” methods, the SVG dimensions default to points (1/72nd inch). So I decided to experiment with different options and see how they are interpreted by the Glowf…

@mhumphrey

IIRC, What I discovered is that Inkscape assumes a DPI value of 96, and will assue this even if there is a viewport element in the SVG that exactly specifies the mapping from physical to user coordinates. Illustrator assumes 72 dpi, but will respect the viewport values if they are there. So what you are describing sounds like exactly the same issue. GFUI assumes 96 dpi, like Inkscape, but unlike Inkscape it will respect the viewport values.

The problems here are, I think, because the user coordinate mapping defined by width, height, and viewbox is is specified in pixels, not real dimensions. I.e., the width and height values either do not have a dimension label, or specify “px”. When saving from Illustrator (using Save As…) the width and height are also defined as pixels, but at 72 dpi.

Thus, importing an Inkscape-saved SVG (be sure to use “plain SVG” instead of “Inkscape SVG”) into Illustrator,all dimensions will grow by 96/72 and going the opposite direction will shrink by 72/96.

The GFUI uses 96 DPI by default, unless it sees a comment in the SVG indicating it was generated by Illustrator.

To enable the two of you to pass SVGs back and forth, editing them in Inkscape and Illustrator, change the width, height, and viewbox attributes as follows:

If the SVG came from Inkscape: width=“20in” height=“12in” viewBox=“0 0 1920 1152”

If the SVG came from Illustrator: width=“20in” height=“12in” viewBox=“0 0 1440 864”

This will mark the SVGs with 20x12 artboards at the correct user units for each. There may be a vertical shift between the two if the source artboard in Inkscape was not 12” high, since Inkscape flips the Y axis, having origin at lower left instead of upper left.