Inkscape scaling again

I’ve gotten myself thoroughly confused by scaling in Inkscape. I’ve read multiple posts, and I think I am OK when I create my own design from scratch, or even from Fusion360 or Festi boxes. But I am still having problems recognizing when someone else’s SVG is going to print correctly.

For example, the files at gift card holder and Art Deco Luggage Tags both show up in Inkscape as too small, even though both have 96dpi set. For the gift card, the hole for the chicago screw shows up at 3.8mm, when it should be ~5mm. 5/3.8 is really close to 96/72. For the luggage tag, the height is 33mm, when I think is should be credit card sized at 54mm. Here, there is no obvious ratio I’m off by. Both of these files do have art boards set to 1440x864, so it may mean that it will work in GFUI; but my question is focused on knowing in Inkscape if the design is correct/accurate.

On the other hand, the files at Easy Kerf Gauges come in exactly correct. 4.0mm circles read as 4.0mm circles. These files also have 96dpi.

So, my question is how can I tell if an SVG is being displayed accurately in Inkscape?

(I have set the option to not include the width of the line in the measurements, so that is not confusing things).

I’ve never even looked at dpi in inkscape, I don’t even know where I would find it.

If you’re downloading other peoples artwork, click on any element of known size and see what it displays. Adjust (the whole design) as needed. You shouldn’t have to mess with dpi settings to “fix” designs that were not drawn to scale.

Coordinates in SVG files are absolute units, not converted from dpi settings (dpi isn’t even specified in plain SVG files, it’s a printer/display setting only.)

But software uses DPI to know how to scale SVGs, so it does matter, actually, even though it’s not in the SVG file itself.

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I’m generally OK with the grab a known element and scale. However, I am concerned about doing this if someone has kerf corrected the file, or even knowing if kerf correction has been applied. For the gift card, if I change the document properties to 72dpi, the hole for the chicago screw become 5.08mm, which looks to be kerf corrected for a 5mm screw. Without knowing this, I would have scaled this to a 5mm hole.

For completeness, in Inkscape you can go to document properties, select “in” as the display unit, and read off the scale in “user units per in”.

So you’re saying the the DPI doesn’t have any effect? That doesn’t appear to follow from what I’ve been reading. For example, there was a huge upset when Inkscape changed from 90 to 96dpi as the default. There are many posts about that, here is one

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I guess I’m just lucky. I’ve never seen dpi specified or had “scaling” issues working with plain SVG files, my own or from other sources, but I only use Inkscape.

Inkscape by default assumes 72 DPI, while GFUI assumes 96. But if you’re saving on a 12x20" art board you won’t have the issues even so, because the GFUI is trained to recognize that and scale correctly.

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If I don’t have a scale to go by, I figure out what a slot using my kerf measurements would need to measure for my material, pick one of their slots, and scale to that.

Only time it hasn’t worked was on a design where their slots weren’t all uniform, and I didn’t think to check for that. :stuck_out_tongue_winking_eye:

I’ve screwed this up and wasted material. I’m looking for a way to know before I cut. I know I can use the camera or rulers for a gross check, but i was looking for something more definitive. this also removes the possibility of accurately editing the file to make any additions.

What happens when you import the SVG you want into an Inkscape document that already has the art board set to 1440x864 (20x12")?

My document default art board is this and I always import into an existing new document rather than just opening the file as is. I seem to always get correct scaling.

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I’ve never defined any “art board”, it appears the default is A4 but I have page borders disabled. I work in mm.

Not sure how it’s assuming 72dpi as it’s not specified in the output (or anywhere in the application that I can tell.)

It occurs to me this may be a raster image issue. I don’t work with rasters in Inkscape.

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Is that correct?

Maybe I’m remembering AD. I do remember having to fix something in Inkscape to make my designs come out the right size, though.

Funny you ask about that. I just had to figure out where the Inkscape beta hides the templates.

No difference. The gift card comes in at the same small size no matter how I import into the glowforge template (using both 96 and 72dpi options on the import)

Not a raster issue. All of the files I linked to are vector.

What do your document properties say?

This is what confuses me the most here. It doesn’t appear to be an Inkscape setting since the kerf gauges import correctly.

It’s all about who designed the SVG and in what software. If their software makes the same DPI assumptions as yours, then everything comes out fine.

Like I said, if you know what size a slot needs to be for your material, taking into account your kerf calculations for your material, scale according to that and you’ll be fine, except on the rare occasions you get a design by a designer who was sloppy and didn’t make them all the same thickness.

Display props in px

Display Props in in:

Even though the scale is 96 units/in, it is being interpreted as 72 units/in to get a 15x9 instead of 20x12

I think the work area size has to be literally specified in the SVG in an actual measurement (something other than pixels), for the GFUI to pick up on it being 12x20.

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