Topology-aware simplification

A very useful feature of a topology is the ability to simplify the feature geometry while maintaining its topological relationships. As we learned in Chapter 2, Spatial Data Analysis, the ST_SimplifyPreserveTopology function doesn't do that, despite its name. In this section, we will learn how to simplify features using topology functions.

Importing sample data

The data used as an example is extracted from the Czech hydrological dataset. Its location was mentioned at the beginning of the chapter, in the The data section. Now we'll import a DIBAVOD watershed layer into a database using ogr2ogr:

ogr2ogr -t_srs EPSG:32633 -f PostgreSQL "PG:dbname=mastering_postgis host=localhost user=osm password=osm" -lco GEOMETRY_NAME=geom -lco PRECISION=no -nln watershed_ord3  A08_Povodi_III.shp 

Next, we will convert the Simple Feature geometry to a topology with 2-meter precision:

SELECT topology.CreateTopology('water_topology', 32633, 1, FALSE); 
SELECT topology.AddTopoGeometryColumn...