In my quest to understand spatial GIS functionality, I have come to the ultimate goal: evaluation the actual database products themselves.
PostgreSQL / PostGIS
PostGIS is a variant of PostgreSQL with spatial extensions. The main reason for maintaining the GIS feature set outside of PostgreSQL proper seems to be licensing: the spatial extensions are
LGPL GPL licensed.
PostGIS is widely recognized as the most mature and feature-rich GIS implementation for SQL databases (and perhaps any database), matched only by the costly Spatial extension for the Oracle Enterprise database. (See comparisons in the links below.)
While the underlying index should be opaque to the user of a DBMS with spatial features, the API used to define spatial types and operate on them is of course more visible. The relevant standard in this space is often referred to as "OpenGIS", however the Open Geospatial Consortium in fact defines a long list of standards. The standard relevant to SQL databases is known more precisely as "OpenGIS Implementation Specification for Geographic information - Simple feature access - Part 2: SQL option" aka "Simple feature access".
It is not meaningful to recite the standard at length in my blog, my focus is instead on actual implementations that I will blog about later. The following points are however worth noting:
I work for a company that is the leading supplier of automotive maps, and wants to be the leading supplier of online maps. So it was only a matter of time that I needed to learn more about how spatial extensions work in different open source databases. Let's start from the beginning, understanding various spatial data structures that are used in implementations...
Links are provided to Wikipedia articles - which are both comprehensive, yet easy to understand - for those who want to get a deeper understanding of each structure. All Wikipedia articles on spatial indexes are listed here: http://en.wikipedia.org/wiki/Spatial_index#Spatial_index