6 Geometry and geography functions

In previous chapters, we’ve discussed PostGIS spatial types—how to create them and how to add them to your database. In this chapter, we’ll introduce the core set of functions that work with the geometry and geography spatial types. This chapter concentrates on functions that work with single geometries and geographies.

PostGIS offers lots of functions and operators, and in this chapter we’ve grouped them by intent of use. This is by no means a rigorous classification, nor one that will neatly sort each function into a unique group without ambiguity, but grouping functions by the type of tasks you’re trying to accomplish is the handiest approach, in our experience. We’ll refer to geometries and geographies as spatial objects when discussing both. This is the classification scheme we’ll use:

6.1  Output functions

6.1.1  Well-known binary (WKB) and well-known text (WKT)

6.1.2  Keyhole Markup Language (KML)

6.1.3  Geography Markup Language (GML)

6.1.4  Geometry JavaScript Object Notation (GeoJSON)

6.1.5  Scalable Vector Graphics (SVG)

6.1.6  Mapbox Vector Tile (MVT) and Protocol Buffers

6.1.7  Tiny WKB (TWKB)

6.1.8  Extensible 3D Graphics (X3D)

6.1.9  Examples of output functions

6.1.10  Geohash

6.2  Constructor functions

6.2.1  Creating geometries from text and binary formats

6.2.2  ST_GeomFromText

6.2.3  ST_GeomFromWKB and ST_GeomFromEWKB

6.2.4  ST_GeomFromGML, ST_GeomFromGeoJSON, ST_GeomFromKML, ST_GeomFromTWKB, ST_GeomFromGeoHash

6.2.5  Creating geographies from text and binary formats

6.2.6  Using text or binary representations as function arguments