Fusion's stupid treatment of SVG files

TomWS · February 17, 2022, 5:33pm

I’ve been messing around with Fusion 360 (version 2.0.12392) lately and, for the most part really like it. However, Fusion’s brain dead treatment of inserted SVG files has me stunned.

Three things are readily apparent when you insert an SVG. First, it’s size is NOTHING like the original file, it’s orientation is off, and, in most cases the offset is seemingly out of whack with the real world.

Fortunately, after a bit of experimentation I realize Fusion’s fatal flaw. I got this while watching an ‘official’ AutoDesk tutorial on inserting SVG. The presenter (someone named Tallis) stated that SVGs are ‘old school’ because they use screen units for dimensions and therefore can’t be relied on.

Well, it is true that the base unit within SVG is, in fact, uses ‘pixels’, but the thing Autodesk ignores is that SVG units are PIXELS PER INCH! A very well defined relationship. Since V0.92 Inkscape has used 96 DPI (pixels per inch) for its internal units.

Running a couple of experiments, I have found the essential first principles when it comes to inserting an SVG into Fusion.

If the Inkscape Page size matches the extents of the object being imported, there will be no offset. One corner will land on your Fusion Sketch origin (or wherever you’re inserting the object). If the Inkscape page size is larger than your object you will get some offset that is somehow related to Autodesk’s misunderstanding of an SVG file - I didn’t bother to pursue this, it didn’t seem worth the effort.
Since Fusion doesn’t seem to know how big SVG’s pixels are, it simply uses the pixel value for anything you’re importing. So… import a 100mm square into Fusion with mm units and you WILL get a square that is 26.4583 mm (by the way, it doesn’t matter if it’s Inkscape SVG or Plain SVG).
If you import the same SVG into a sketch with Inch units, you WILL get a square that is 1.0417 inches.

Why, you ask, does this happen? Because Fusion ignores the SIZE of a pixel. A pixel at 96 DPI is exactly 0.264583mm. A pixel at 96 DPI is exactly 0.010417 Inches.

So, how do you get around this? Simple. When you import the SVG, change the scale factor in the insert dialog (BEFORE you do anything else) from 1.00 to 3.779528. How did I get that magic number?
3.779528 = 1/0.264583 of course…

Interestingly, the same scale number works if you insert into a sketch in inch units. Again, I’m not gonna bother to pursue why…

So, here are some pics of my experiments and results:

TinWhisperer · February 17, 2022, 5:40pm

So this will only work for SVG files that are created with inkscape @ 96dpi?

One of the old school auto desk guys he has lots of YouTube videos and he’s on their forum site all the time.

How would the workflow above react to using a Adobe illustrator produced SVG?

After you insert an SVG into fusion 360 you could rescale the whole sketch based on one known dimension and then it would proportionally.

This is a good little article of trying to go from a dxf to an SVG with fusion 360. Not really the correct direction you’re looking for but a little more info.

I rarely use imported SVG s in fusion 360 for anything that’s dimensionally important.

I typically just use svgs for art stuff and DXF for everything else.

Here’s the little blurp on how to deal with it on the fusion 360 site for anyone else is interested in this topic.

SVG file imports with a wrong scale into Fusion 360 | Fusion 360 | Autodesk Knowledge Network)%20and%20press%20OK.

Other people are using the multiplier of 1.333333 for scaling out of Adobe illustrator created svgs

TomWS · February 17, 2022, 6:22pm

Well if you use software that uses 96DPI, which is practically any software on the planet (unless it, of course, was developed by Autodesk). And since SVG knows what a spline and bezier curve is, I expect much more accuracy from SVG than from a DXF.

The key point here, however, is that Autodesk completely ignores Pixel SIZE, leaving SVG floating out in the wind…

But, to each his own, I’ll use SVG.

TomWS · February 17, 2022, 6:53pm

Ah, so that’s why Affinity Designer offers 72DPI, that’s what Adobe Illustrator must use. (96/72=1.3333333333333333). Affinity has presets at 72, 90, 92, and 96 plus you can use your own custom one if you live on a different planet, I guess…

SWomack · February 17, 2022, 7:41pm

I bought Affinity Designer last fall and its really easy to use and when you export at 96dpi and import in sheetcam at 96 dpi it works great.

jamesdhatch · February 18, 2022, 3:48am

That’s pretty funny from someone whose company pushes DXF, a really old format that generally does not support bezier curves (technically the standard can, it’s just that virtually everyone implements the lowest common denominator version of the spec). It’s also not uncommon for them to come through unit-less as well - the receiving app needs to scale it (which is why 1:25.4 is a magic scaling number to try when importing a DXF).

TomWS · February 18, 2022, 6:15pm

As an update to the foolishness of Fusion 360’s handling of SVGs…

Today I decided to try to import a design I’ve been working on for a while. Originally started in Affinity Designer, but then moved to Sketchup because I needed a 3D view, then refined in Inkscape because I wanted smoother curves, and finally imported into V-Carve Pro to prep for carving on my CNC Router.

ALL of these moves were done by passing SVGs between all the programs without any issues.

Today I decided to export the vectors that I’ve refined from V-Carve, as SVG, of course. Realizing that the SVG page size might give Fusion some grief, I decided to import into Inkscape to fix that problem. I was pleasantly surprised that V-Carve not only set the page size to a proper value but also kept the paths with the same layer names as the layers in V-Carve - very friendly service indeed. In any case, I decided to move a couple of object to some new layers and then saved from Inkscape.

Ok, time to insert into Fusion 360!

Well, that didn’t go as expected. From my previous experiments I was sure I’d only have to scale by 3.779528 and I’d be golden! uh, no way. I had to scale it by 96 to get the correct size in Fusion. 96!!! What the hell??? I have no idea why this data that moved around so easily between all the other programs now can’t even move from Inkscape to Fusion in a predictable way!

In any case, I guess the net is: SVG Import is great, but expect to do SOMETHING to get Fusion to process it properly… No wonder the old timer said you can’t rely on it!!! Fusion is way too whimsical in its treatment of SVGs!

Heath · February 19, 2022, 6:52am

Fusion has a add on for dxf now thst I just found on the app store that will close the open loops when inserted and has alot more importing options than the standard dxf insert.It seems to work good for me.