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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.

API/ABI Stability

Note that all releases are version 0.x, so there are no API or ABI stability guarantees. Starting with 1.0 we will adhere to SemVer.

The Python API is particularly unstable, and it is planned that the SWIGged API will be replaced by a pybind11 version with more Pythonic names and more complete functionality.

Requirements for End Users using Bazel

Build

This bazel build requires 7.0.0 – bzlmod default. Builds were tested using C++20 as set in .bazelrc. This setup relies on abseil-cpp, boringssl, and googletest from the bazel central repository as set in MODULE.bazel.

To build and test using bazel, from within s2geometry/src, run:

bazel test "//:*"

To build the libary without testing, from within s2geometry/src, run:

bazel build //:s2

Status

All tests enumerated in the BUILD.bazel file pass on x86 machines. On Apple M1, s2loop_measures_test fails due to a 6% excess accumlated error. This issue may require revision of boringssl or exactfloat.

Requirements for End Users using CMake

• CMake
• A C++ compiler with C++14 support, such as g++ >= 5
• Abseil >= LTS 20240116 (standard library extensions)
• OpenSSL (for its bignum library)
• googletest testing framework >= 1.10 (to build tests and example programs, optional)

On Ubuntu, all of these other than abseil can be installed via apt-get:

sudo apt-get install cmake googletest libssl-dev

Otherwise, you may need to install some from source.

Currently, Abseil must always be installed from source. See the use of -DCMAKE_PREFIX_PATH in the build instructions below. This is likely to change.

On macOS, use MacPorts or Homebrew. For MacPorts:

sudo port install cmake openssl

Do not install gtest from MacPorts; instead download release 1.10.0, unpack, and substitute

cmake -DGOOGLETEST_ROOT=/...absolute path to.../googletest-release-1.10.0 ..

in the build instructions below.

Thorough testing has only been done on Ubuntu 14.04.3 and macOS 10.12.

Build and Install

You may either download the source as a ZIP archive, or clone the git repository.

Via ZIP archive

Download ZIP file

cd [parent of directory where you want to put S2]
unzip [path to ZIP file]/s2geometry-master.zip
cd s2geometry-master

Via git clone

cd [parent of directory where you want to put S2]
git clone https://github.com/google/s2geometry.git
cd s2geometry

Building

First, install Abseil. It must be configured with -DCMAKE_POSITION_INDEPENDENT_CODE=ON. s2geometry must be configured to use the same C++ version that abseil uses. The easiest way to achieve this is to pass -DCMAKE_CXX_STANDARD=14 (or -DCMAKE_CXX_STANDARD=17) to cmake when compiling both abseil and s2geometry.

From the appropriate directory depending on how you got the source:

mkdir build
cd build
# You can omit -DGOOGLETEST_ROOT to skip tests; see above for macOS.
# Use the same CMAKE_CXX_STANDARD value that was used with absl.
cmake -DGOOGLETEST_ROOT=/usr/src/googletest -DCMAKE_PREFIX_PATH=/path/to/absl/install -DCMAKE_CXX_STANDARD=14 ..
make -j $(nproc)
make test ARGS="-j$(nproc)"  # If GOOGLETEST_ROOT specified above.
sudo make install

On macOS, sysctl -n hw.logicalcpu is the equivalent of nproc.

Disable building of shared libraries with -DBUILD_SHARED_LIBS=OFF.

Enable the python interface with -DWITH_PYTHON=ON.

If OpenSSL is installed in a non-standard location set OPENSSL_ROOT_DIR before running configure, for example on macOS:

OPENSSL_ROOT_DIR=/opt/homebrew/Cellar/openssl@3/3.1.0 cmake -DCMAKE_PREFIX_PATH=/opt/homebrew -DCMAKE_CXX_STANDARD=17

Installing

From build subdirectory:

make install

Prefix it with sudo if needed:

sudo make install

NOTE: There is not uninstall target but install_manifest.txt may be helpful.

All files will be installed at location specified in CMAKE_INSTALL_PREFIX variable.

Several suffix variables used for some file groups:

If needed set this variables on command line as cmake arguments with -D prefix or edit from build subdirectory:

make edit_cache

For more info read: The CMake Cache.

Python

If you want the Python interface, you need to run cmake using -DWITH_PYTHON=ON. You will also need to install the following dependencies:

• SWIG 4 (for Python support, optional)
• python3-dev (for Python support, optional)

which can be installed via

sudo apt-get install swig python3-dev

or on macOS:

sudo port install swig

Version 4.0 is required, but it should be easy to make it work 3.0 or probably even 2.0.

Python 3 is required.

Creating wheels

First, make a virtual environment and install build into it:

python3 -m venv venv
source venv/bin/activate
pip install build

Then build the wheel:

python -m build

The resulting wheel will be in the dist directory.

If OpenSSL is in a non-standard location make sure to set OPENSSL_ROOT_DIR; see above for more information.

Other S2 implementations

• Go (Approximately 40% complete.)
• Java
• Kotlin (Complete except binary serialization)

Disclaimer

This is not an official Google product.