Fusion 360 Polygon Edge Conversion Issues

tkelley8VDR5 — Fri, 21 Oct 2022 15:42:35 GMT

We discovered that Fusion 360 automatically converts curved polygon edges to linearized representations of the curve (line segments) when exporting back to an Eagle-compatible board or library file. This includes creating a new version of a managed library! Unfortunately this makes it extremely difficult to change the curve in Eagle.

In Fusion 360:

In Eagle (after exporting to an Eagle 9.x compatible board file):

Some background: We typically do all of our design work in the standalone Eagle, but in this instance we needed to edit the managed library in Fusion 360. We noticed this issue after creating a new version of the managed library from Fusion 360.

@jorge_garcia - Is converting a curved polygon edge to line segments the intended operation, or is this a bug? I would think the latter, since Fusion 360 supports the curve property of polygon edges and should be able to save that curve value into a BRD file or managed library as part of a polygon <vertex> (in the XML) like Eagle does.

While investigating, we also noticed that Fusion 360 automatically "corrected" all polygon edge widths that were 0 to 0.1524mm. Fortunately, it seems like Fusion 360 does attempt to convert polygon edge endpoint locations when importing/exporting from/to Eagle because of the new polygon rendering method, so that the polygon fill is the same in Eagle and Fusion 360. However, it appears that Fusion 360 did NOT update the endpoint locations when it automatically made changes to the managed library data! So effectively all of our zero-width polygons just grew by ~3mil in each direction. We do realize that zero-width polygons are not recommended, but Fusion 360 should not be automatically making changes like this (that can affect a design) without at least warning us.

Before saving managed library in Fusion 360:

After saving managed library in Fusion 360:

@jorge_garcia - Is this polygon edge width conversion without updating the polygon edge endpoint locations the intended operation, or is this a bug? I would think the latter, since Fusion 360 does the conversion as best it can when importing an Eagle board file or exporting back to one.

I think I can (relatively) easily correct the polygon widths in our managed library, but correcting the change from curves to line segments will be much more difficult.

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Fusion 360 Polygon Edge Conversion Issues