VW+midpoint smoothing creates broken polygon

[wipfli]

Describe the bug
Running VW simplification followed by midpoint smoothing results sometimes in broken polygons.

To Reproduce
Steps to reproduce the behavior:

1. clone https://github.com/wipfli/debug-assets/tree/main/midpoint
2. Run command run-vw.sh
3. See error in map at http://[::]:8080/data/pmtiles/[FEATURE] Add utility to abbreviate road names #14.3/47.12837/7.97538

Expected behavior
The forest should not have a hole.

Screenshots

Environment (please complete the following information):
ubuntu laptop

Additional context
This came up while looking for a reproduction of #1262

[msbarry]

Looks like that hole is right at the intersection of 4 tiles... so what's going on is that the simplified shape has a corner just outside the edge of the tile, and midpoint smoothing chops off the corner:

I accounted for this in DualMidpointSmoother by adding a maxVertexOffset/maxVertexArea parameter where you can specify the maximum distance that smoothing is allowed to displace the line from it's original geometry. var smoother = DualMidpointSmoother.chaikin(1).setMaxVertexOffset(1); makes it look like this:

Seems like we'd probably want to add maxVertexOffset/maxVertexArea parameter to midpoint smoother. Or just say that midpoint smoothing is only meant to be done on geometryies prior to tiling, not in post-process?

[wipfli]

Thanks for investigating! Both sound good to me.