The goal of this recipe is identical to the previous two recipes, but it covers how to perform the process with data in a PostGIS database. You will use it to turn points into lines, and lines into polygons.
Not all methods are available; for those not available, you can use the previous recipe. It will also work on a database layer; it just doesn't save the results to the database. So, the results will need to be imported to the database after completion.
You need to load a vector layer of points with a numeric ID indicating order, and an identifier of unique lines or polygons that is shared between points of the same geometry. For example, you can use census_wake_2000_points loaded into PostGIS with the geometry field called geom. (Refer to Chapter 1, Data Input and Output, the Loading Vector Data into PostGIS recipe to see how to load data into PostGIS.)