A C++ header-only Polyline Encoder/Decoder

C++ implementation of Google Encoded Polyline Algorithm Format.
The implementation guarantees to conform with the results of the Google Interactive Polyline Encoder Utility.

Prerequisites

No special requirements except C++11 compliant compiler. The class is tested with gcc and MSVC compilers. In order to build and run unit tests for this project you are required to have Google Test library installed on the system. For more details see the CI badges or GitHub Actions.

Installation

As Polylineencoder is a single header library no installation required in general. Just include polylineencoder.h in your project and instantiate gepaf::PolylineEncoder class template.

Integration with CMake projects

However, if you use CMake and want to integrate the library into your project you might want to install it first by invoking a CMake command from the build directory:

cmake --install . --prefix=<install_path>

Once the library is installed you can use it from in your project by adjusting its CMake script. For example:

[..]
find_package(polylineencoder REQUIRED)

add_executable(example main.cpp)
target_link_libraries(example gepaf::polylineencoder)
[..]

Usage Example:

All code is in gepaf namespace. gepaf stands for Google Encoded Polyline Algorithm Format.

#include <polylineencoder.h>

// Create an encoder with precision of five decimal places (default)
// In order to create objects with other precision use template parameter
// like: gepaf::PolylineEncoder<6>
gepaf::PolylineEncoder<> encoder;

// Poles and equator.
encoder.addPoint(-90.0, -180.0);
encoder.addPoint(.0, .0);
encoder.addPoint(90.0, 180.0);

auto res = encoder.encode(); // "~bidP~fsia@_cidP_gsia@_cidP_gsia@"
encoder.clear(); // Clear the list of points.

// Decode a string using static function.
auto polyline = gepaf::PolylineEncoder<>::decode("~bidP~fsia@_cidP_gsia@_cidP_gsia@");

// Iterate over all points and print coordinates of each.
for (const auto &point : polyline) {
    printf("(%f, %f)\n", point.latitude(), point.longitude());
}

You can also use custom data structures and containers including C-style arrays.

class Point
{
public:
    Point(double t_x, double t_y) : x(t_x), y(t_y) {}

    double getX() const { return x; }
    double getY() const { return y; }

    double x;
    double y;
};

gepaf::PolylineEncoder<> encoder;

// List of DummyPoint for testing purpose
DummyPoint dp[] = {
    Point{-90.0, -180.0},
    Point{.0, .0},
    Point{90.0, 180.0}
};

// Using member functions.
auto result1 = encoder.encode(dp, dp + sizeof dp / sizeof dp[0], &DummyPoint::getX, &DummyPoint::getY);

// Using member variables.
auto result2 = encoder.encode(dp, dp + sizeof dp / sizeof dp[0], &DummyPoint::x, &DummyPoint::y);

Building and Testing

There are unit tests provided for PolylineEncoder class template. You can find them in the test/ directory. To run them you have to build and run the test application (linking with Google Test library is required). For doing that you can invoke the following commands from the terminal, assuming that compiler and environment are already configured:

Linux (gcc)

cd test
g++ -std=c++11 -I..\src main.cpp -o test
./test

or with CMake

mkdir build && cd build
cmake .. -DENABLE_TESTING=True
make
make test

Windows

cd test
cl /W4 /EHsc /I..\src main.cpp /link /out:test.exe
test

or with CMake

mkdir build && cd build
cmake .. -G "NMake Makefiles" -DENABLE_TESTING=True
cmake --build . --config Release
ctest -C Release

See Also

• Encoded Polyline Algorithm