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S2 Geometry Library

Overview

This is a package for manipulating geometric shapes. Unlike many geometry libraries, S2 is primarily designed to work with spherical geometry, i.e., shapes drawn on a sphere rather than on a planar 2D map. This makes it especially suitable for working with geographic data.

If you want to learn more about the library, start by reading the overview and quick start document, then read the introduction to the basic types.

S2 documentation can be found on s2geometry.io.

Build and Install

You may either download the source as a ZIP archive, or clone the git repository. The Java packages are built and tested using Maven.

In the directory containing the pom.xml file, use Maven to compile the package, run tests, and install the package. For example:

mvn clean
mvn compile
mvn test
mvn package
mvn install

Benchmarks

After building packages, a "benchmarks.jar" file may be found in benchmarks/target/. Benchmarks can then be run with the command java -jar benchmarks/target/benchmarks.jar Parameters for the benchmarks can be passed on the command line. For example, to run just the S2Loop benchmarks, java -jar benchmarks/target/benchmarks.jar S2Loop

S2 implementations

The S2 library has implementations in several languages. In addition to this Java implementation, Google provides:

  • C++ (The reference implementation and the most full featured).
  • Go (Approximately 40% complete.)
  • Python

We (the S2 developers) aim to provide similar classes and APIs across all implementations, while adapting to language idioms where that makes sense, and changing APIs where required for good performance. The implementations have varying degrees of completeness and maturity. This Java implementation is heavily used within Google and is generally mature, aside from the newest features, but is not as complete as C++.

2022 Q4 Release Highlights

Many improvements have been made to the Java implementation of S2 since the last release in September 2021. Some highlights:

  • Implementations of S2ClosestEdgeQuery and S2FurthestEdgeQuery, as well as S2ChainInterpolationQuery and S2HausdorffDistanceQuery.

  • New tools for clustering and sharding data: S2RegionSharder and S2DensityTree.

  • Support for map projections in MercatorProjection, PlateCarreeProjection, and S2EdgeTesselator.

  • S2Coder implementations are now complete and should be interoperable between Go, C++ and Java.

  • New Java implementation benchmarks based on JMH, the Java Microbenchmark Harness.

  • Addition of S2IndexingHelper, which supports spatial indexing of regions in documents and finding document regions that intersect a query region.

  • Many new methods on existing classes adding features which had formerly been missing in Java compared to the C++ implementation.

  • Many Javadoc and other comment improvements.

  • Many implementation cleanups. Most should not cause visible changes, but there were some bug fixes for improved accuracy.

  • @CheckReturnValue is a package-wide default now, set in the newly added "package-info.java".

  • The "testdatagenerator" subpackage supports generation of test data for both benchmarks and unit tests. Note that the APIs in this package are not part of the external S2 API and are subject to change without notice.

Breaking API changes:

  • We are now using Java 11, updating from Java 8, and beginning to use Java 11 language features.

  • Class Matrix3x3 was renamed Matrix.

  • S2.simpleCrossing(a, b, c, d) has been removed as redundant; S2EdgeUtil provides the same API along with robustCrossing() and the EdgeCrosser class.

  • A bug fix for EdgeCrosser.robustCrossing() may break clients that were relying on robustCrossing() to detect both repeated vertices in polylines and self-intersecting polylines. Specifically, for degenerate edges that don't have shared endpoints, robustCrossing now returns -1 to indicate "No Crossing" while previously it would return 0. Now, a return value of 0 is used only to indicate that two points from different edges are the same, i.e. edges touch. This now behaves exactly like the equivalent CrossingSign() in C++ for degenerate edges.

  • Removed S2CellId.toTokenOld().

  • The nested class RangeIterator was moved from S2ShapeIndex to S2ShapeUtil.

  • The nested classes AreaMeasure, CentroidMeasure, and AreaCentroidMeasure were removed as they were redundant. Instead, use the methods in S2ShapeMeasures to compute centroids and areas for S2Shapes.

  • Support for GWT has been removed. Support for J2CL is in progress but incomplete. The JS API is not final.

Disclaimer

This is not an official Google product.

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