6a Intermission The OGC simple feature specification

Before we continue coding, we need to understand some terms that will be used in the following chapters. The spatial objects we use are objects defined by the OGC simple feature specification. You don't have to read the document, just to understand the three basic topics:

1. Geometric types

Basically point, line and polygon. And compositions of these types. Note: Polygons can not be described by a single sequence of points. They can have islands and holes (and islands within holes). Here are two multipolgons: Rastatt and Baden-Baden. Rastatt has a hole that is filled out by Baden-Baden. But inside this hole there are some enclaves of Rastatt that are holes of the Baden-Baden polygons.

2 Operations and predicates on these types

You can also check the relation between two geometries (intersects or contains).

3. Binary and texual representations

Objects can be serialized binary (well-known-binary WKB) or textual (well-known-text WKT) GeoJson is no OGC-standard, but quite similar to WKT