Double Offset on Select Polylines

[wildspidee]

This is on Windows 8.1, QCAD version 3.14.3.0 (although it was happening on my old 3.12, too). I've got curves that I've converted (exploded) to polylines so that I can offset them. The Polyline offset works on some curves, I can choose either side, but on others it does a double offset. I'm not changing any tool settings between these offsets. I don't know what I'm doing that causes this to occur. I certainly don't want or need a double offset.

I've attached an image that shows the top line offset perfectly and the side one with doubles.

Any ideas?

[Clive]

If possible would you be able to attach the cad file or similar for testing.

[wildspidee]

Sure. Here is the file. It's a bit of a mess, but you can clearly see the issue.

Thanks Clive.

[andrew]

The current (3rd party) offset algorithm actually always creates an offset polyline on both sides. QCAD tries to remove the offset on one side if possible. Unfortunately, this is not always possible as sometimes QCAD cannot identify the exact limits. This is often the case if the polyline has many very small segments as in this case.

One way to improve the situation is to simplify the original polyline first:
- Select polyline
- Draw > Polyline > Simplify
- Enter a tolerance at the top of 1 (degree) and click the apply button (green check mark)

The polyline now has a lot less nodes and it should be possible to create an offset on one side only.

[wildspidee]

Thank you Andrew. I'll follow those steps and hopefully it will resolve the issue.