Working with pgRouting - PostGIS - page 324

Extracting the centerlines of polygons

In several recipes in Chapter 4 , Working with Vector Data - Advanced Recipes , we
exploredextractingVoronoipolygonsfromsetsofpoints.Inthisrecipe,we'llusethe
Voronoifunctionemployedinthe Using external scripts to embed new functionality in
order to calculate a Voronoi diagram recipe,in Chapter4 , Working with Vector Data
- Advanced Recipes ,toserveasthefirststepinextracting thecenterlineofapoly-
gon.Onecouldalsousethe Using external scripts to embed other libraries in order
to calculate a Voronoi diagram - advanced recipe,in Chapter4 , Working with Vector
Data - Advanced Recipes ,whichwouldrunfasteronlargedatasets.Forthisrecipe,
we will use the simpler but slower approach.

One additional dependency is that we will be using the
chp02.polygon_to_line(geometry) function from the Normalizing

internal

overlays recipe in Chapter 2 , Structures that Work .

Whatdowemeanbythecenterlineofapolygon?Imagineadigitizedstreambetween
its pair of banks as shown in the following screenshot: