algorithmgeometrypolygoncomputational-geometrybuffering

An algorithm for inflating/deflating (offsetting, buffering) polygons

How would I "inflate" a polygon? That is, I want to do something similar to this:

alt text

The requirement is that the new (inflated) polygon's edges/points are all at the same constant distance from the old (original) polygon's (on the example picture they are not, since then it would have to use arcs for inflated vertices, but let's forget about that for now ;) ).

The mathematical term for what I'm looking for is actually inward/outward polygon offseting. +1 to balint for pointing this out. The alternative naming is polygon buffering.

Results of my search:

Here are some links:

Solution

  • August 2022:
    Clipper2 has now been formally released and it supersedes Clipper (aka Clipper1).

    I thought I might briefly mention my own polygon clipping and offsetting library - Clipper.

    While Clipper is primarily designed for polygon clipping operations, it does polygon offsetting too. The library is open source freeware written in Delphi, C++ and C#. It has a very unencumbered Boost license allowing it to be used in both freeware and commercial applications without charge.

    Polygon offsetting can be performed using one of four styles (or Join Types) - mitered, squared, bevel and round.
    mitered square bevel round
    Note: In JoinType.Miter, the inner angle at vertex A is more acute than the one at B and the mitered offset at A would exceed the specified miter limit of 2.