Visualizing computational geometry concepts using JTS TestBuilder

In this post, I would like to let you know about an excellent piece of software, Java Topology Suite (JTS).

JTS is an open source library of spatial predicates and functions for processing geometries. It provides a complete, consistent, and robust implementation of fundamental algorithms for processing linear geometry on the 2-dimensional Cartesian plane.

A funny thing about it is that JTS

is used by most java based Open Source geospatial applications, and GEOS, which is a C++ port of JTS, is used by most C based applications.

So, all the downstream projects using GEOS such as various Python wrappers around GEOS such as shapely and even the PostgreSQL extension, PostGIS, all of them really work against the JTS using the GEOS as the interface for communication. So the JTS is a very, very powerful Java library.

If you are not a Java developer, though, this might be of little interest to you. However, there is another little application, called JTS TestBuilder, which provides a GUI for geometry exploration and is an interface into the JTS API. It is not so famous as other pieces of open source GIS stack, such as QGIS or GRASS, though. Also its documentation is outdated and scarce, so you would need to find out how to use the application on your own.

Nevertheless, it is an indispensable tool for anyone who spends a fair amount of time working with computational geometry or spatial data processing applications. It would also serve as a great visualization tool for GIS instructors who need to visually explain how GIS algorithms operate. I have used it to show how Convex Hull is created from a set of points, for instance. One obvious advantage of JTS TestBuilder is that you do not need to run any heavy GIS applications and the “geometry modification – running analysis – seeing the result” cycle is really short.

Here I’ve loaded cities of California along with the state boundary and created a convex hull for the boundary geometry.

2018-03-14 17_41_18-JTS TestBuilder

Having said that, you can work in the following manner:

  • Use your favorite GIS database management tool to get WKT of a geometry you would like to inspect or analyze.
  • Use the JTS TestBuilder to draw the features.
  • Run JTS Geometry Functions constructing new geometries or answering spatial questions.
  • Load the results of the analysis back into your GIS (either for ad hoc exploration or for storage).

The code to read the features into WKT and write back from WKT using arcpy:

 

JTS TestBuilder can also help you to learn something new with regard to GIS theory. If you think that you are a well seasoned GIS professional who can amaze others by mentioning a few cool names like Voronoi or Thiessen, I encourage you to explore the geometry functions JTS TestBuilder provides. I am pretty sure just a few of you have heard of:

  • Koch snowflake which are used a lot in space-filling as well as cartographic simplifaction algorithms.
  • Seirpinski carpet which is not used extensively in GIS yet, but there are some emerging applications regarding urban pattern analysis.

If you would like to take advantage of the computational geometry algorithms implemented in JTS, there are also ports to .NET and JavaScript.

Another very similar application that is particularly popular among math teachers is GeoGebra. I have been using it for a while, too, but it lacks export of result geometries into WKT which can be put into a geospatial database or drawn directly in a desktop GIS application such as ArcMap or QGIS. You can try GeoGebra online or by installing a desktop application. It is also available as an app for iOS, Android, and Windows Phone.

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