One of the best ways to get started using the GEOS library with C++ is to use Conan and CMAKE.

GEOS is the Geometry Engine, Open Source library written in C and C++. Is is a port of the Java Topology Suite (JTS). Both libraries include spatial predicate functions and spatials operators. GEOS is used extensively in the PostGIS extension for Postgres. Conan is a C/C++ package manager. It allows you to declare what libraries your code depends on. Finally, CMake is one of the most popular ways to build C++ applications.

Let’s build a GEOS hello world style application. First you need to install conan and CMAKE.

Then, create a conanfile.txt file. This declares that our code depends on GEOS version 3.8.1.

[requires]
geos/3.8.1

[generators]
cmake_find_package

After that, create a CMakeLists.txt file. This basically says that we require CMAKE 3.1 or higher, we need C++11, and that we are building an executable program using a single file called main.cpp that depends on the GEOS library.

project(geos)
cmake_minimum_required(VERSION 3.1)

set (CMAKE_CXX_STANDARD 11)
set(CMAKE_MODULE_PATH ${CMAKE_BINARY_DIR})
message(${CMAKE_BINARY_DIR})

add_executable(app main.cpp)
find_package(geos)
target_link_libraries(app GEOS::GEOS)

Now we are ready to create our simple C++ GEOS application. After declaring a few includes, we read in a WKT string, buffer the resulting geometry by 2, and then write the buffered geometry back to WKT and the standard output stream.

#include <iostream>
#include <geos/io/WKTReader.h>
#include <geos/io/WKTWriter.h>
#include <geos/geom/Geometry.h>

int main() {

    geos::io::WKTReader reader;
    auto geometry = reader.read("POINT (1 1)");
    
    auto buffer = geometry->buffer(2, 10);

    geos::io::WKTWriter writer;
    auto wkt = writer.write(buffer.get());
    std::cout << wkt << std::endl;
    
    return 0;
}

Now we are ready to build. Cross your fingers.

First, create a build directory.

mkdir build
cd build

Then install the GEOS dependecy using conan.

conan install ..

Create the CMake build.

cmake ..

Now build the your application.

make

If this builds correctly, you can now run your simple GEOS application.

./app

You should see the WKT of a Polygon.

POLYGON ((3.0000000000000000 1.0000000000000000, 2.9753766811902755 0.6871310699195385, 2.9021130325903073 0.3819660112501058, 2.7820130483767365 0.0920190005209074, 2.6180339887498958 -0.1755705045849452, 2.4142135623730963 -0.4142135623730938, 2.1755705045849485 -0.6180339887498936, 1.9079809994790962 -0.7820130483767345, 1.6180339887498980 -0.9021130325903062, 1.3128689300804655 -0.9753766811902749, 1.0000000000000042 -1.0000000000000000, 0.6871310699195428 -0.9753766811902762, 0.3819660112501100 -0.9021130325903086, 0.0920190005209113 -0.7820130483767382, -0.1755705045849418 -0.6180339887498982, -0.4142135623730911 -0.4142135623730989, -0.6180339887498916 -0.1755705045849507, -0.7820130483767331 0.0920190005209015, -0.9021130325903055 0.3819660112500999, -0.9753766811902747 0.6871310699195328, -1.0000000000000000 0.9999999999999944, -0.9753766811902764 1.3128689300804561, -0.9021130325903088 1.6180339887498896, -0.7820130483767382 1.9079809994790886, -0.6180339887498982 2.1755705045849418, -0.4142135623730989 2.4142135623730914, -0.1755705045849509 2.6180339887498913, 0.0920190005209014 2.7820130483767329, 0.3819660112500998 2.9021130325903055, 0.6871310699195325 2.9753766811902747, 0.9999999999999943 3.0000000000000000, 1.3128689300804561 2.9753766811902764, 1.6180339887498896 2.9021130325903091, 1.9079809994790886 2.7820130483767382, 2.1755705045849414 2.6180339887498985, 2.4142135623730909 2.4142135623730994, 2.6180339887498913 2.1755705045849512, 2.7820130483767329 1.9079809994790988, 2.9021130325903055 1.6180339887499002, 2.9753766811902747 1.3128689300804675, 3.0000000000000000 1.0000000000000000))

• geos
• c++
• conan
• cmake