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JTS FAQ

Q: What is the relationship between JTS and GeoTools?

We make use of the Java Topology Suite to represent “Simple” Geometry, and the OpenGIS interfaces to represent everything else. We have been forced to define an API module of our own in a few cases, like data access, where something “standard” is not available.

You will be using JTS a lot as it literally is the “shape” of GeoTools. It captures shapes using constructs like Coordinate, Point, Polygon and LineString.

  • Do keep in mind that JTS is pure topology and the Geometry objects are pure shapes with no meaning. For the meaning, placing that shape on the earth, you will need to consult a CoordinateReferenceSystem.
  • JTS topologic operations work in a two dimensional cartesian plane. With this in mind three dimensional shapes can be represented, but not calculated with.
  • JTS focuses on linear topology, you will need to represent curves as a LineString with many little segments.

With those notes it may sound like JTS is limited; it is instead focused on the task at hand - Geographic Information Systems. While 3D and curves may be common in CAD systems we will need a lot of funding and raw science to make it work for GIS. Some of that work is happening in GeoTools with ISO Geometry.

Q: What Geometry Specifications?

JTS is an implementation of the OGC Simple Features for SQL Specification (ie SFSQL). It covers 2D constructs like Point, Line and Polygon. JTS is willing to carry a 3rd point around but does not use it for calculations - making it a 2.5D solution for cartesian space.

Specification Supports Implementation
Simple Features for SQL 2.5D, linear Java Topology Suite
ISO Geometry 3D, curves OpenGIS ISO Geoemtry interfaces

GeoTools makes a point of working with both implementations, but frankly the ISO Geometry implementations are not ready yet.