Centroid within non-convex 2d polygon

centroidgeometrypolygons

The centroid of an object is defined as the arithmetic mean of all points of the object. For non-convex objects, the centroid is often not a part of the object itself:

Polygon with centroid outside the object

Is there a definition of a centroid-like point which always lies within the object?

Polygon with centroid within the object

A definition that tackles 2 dimensional polygon objects is sufficient. I could think of something like the following, however, I would prefer a well-known definition if there is one:

  1. Let $s_p(a, b)$ be the shortest path from $a \in p$ to $b \in p$ such that all points of the path are within $p$.

  2. Let $S_p := \{s_p(a, b) | a, b \in p\}$.

  3. Let $d$ be the longest path in $S_p$.

  4. The mid point of $d$ is a centroid-like point and it always lies within $p$.

Best Answer

In geography there is an interesting point called Pole of inaccessibility: the most distant internal point from the polygon outline.

It is found by an iterative method, described in the Methodology section of this paper.

Links of interest:

https://sites.google.com/site/polesofinaccessibility/

https://github.com/mapbox/polylabel

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