Function encodePolyline

include/engine/polyline_compressor.hpp:22–49

template <unsigned POLYLINE_PRECISION = 100000>
std::string encodePolyline(CoordVectorForwardIter begin, CoordVectorForwardIter end)
{
    double coordinate_to_polyline = POLYLINE_PRECISION / COORDINATE_PRECISION;
    auto size = std::distance(begin, end);
    if (size == 0)
    {
        return {};
    }

    std::string output;
    // just a guess that we will need ~4 bytes per coordinate to avoid reallocations
    output.reserve(size * 4);

    int current_lat = 0;
    int current_lon = 0;
    for (auto it = begin; it != end; ++it)
    {
        const int lat_diff =
            std::round(static_cast<int>(it->lat) * coordinate_to_polyline) - current_lat;
        const int lon_diff =
            std::round(static_cast<int>(it->lon) * coordinate_to_polyline) - current_lon;
        detail::encode(lat_diff, output);
        detail::encode(lon_diff, output);
        current_lat += lat_diff;
        current_lon += lon_diff;
    }
    return output;
}

// Decodes geometry from polyline format
// See: https://developers.google.com/maps/documentation/utilities/polylinealgorithm