osrm-backend/src/engine/guidance/assemble_overview.cpp

#ifndef ENGINE_GUIDANCE_ASSEMBLE_OVERVIEW_HPP
#define ENGINE_GUIDANCE_ASSEMBLE_OVERVIEW_HPP

#include "engine/guidance/leg_geometry.hpp"
#include "engine/douglas_peucker.hpp"
#include "util/tiles.hpp"

#include <vector>
#include <tuple>
#include <numeric>

namespace osrm
{
namespace engine
{
namespace guidance
{
namespace
{

unsigned calculateOverviewZoomLevel(const std::vector<LegGeometry> &leg_geometries)
{
    util::FixedLongitude min_lon{std::numeric_limits<int>::max()};
    util::FixedLongitude max_lon{-std::numeric_limits<int>::max()};
    util::FixedLatitude min_lat{std::numeric_limits<int>::max()};
    util::FixedLatitude max_lat{-std::numeric_limits<int>::max()};

    for (const auto &leg_geometry : leg_geometries)
    {
        for (const auto coord : leg_geometry.locations)
        {
            min_lon = std::min(min_lon, coord.lon);
            max_lon = std::max(max_lon, coord.lon);
            min_lat = std::min(min_lat, coord.lat);
            max_lat = std::max(max_lat, coord.lat);
        }
    }

    return util::tiles::getBBMaxZoomTile(toFloating(min_lon), toFloating(min_lat),
                                         toFloating(max_lon), toFloating(max_lat))
        .z;
}

std::vector<util::Coordinate> simplifyGeometry(const std::vector<LegGeometry> &leg_geometries,
                                               const unsigned zoom_level)
{
    std::vector<util::Coordinate> overview_geometry;
    auto leg_index = 0UL;
    for (const auto geometry : leg_geometries)
    {
        auto simplified_geometry =
            douglasPeucker(geometry.locations.begin(), geometry.locations.end(), zoom_level);
        // not the last leg
        if (leg_index < leg_geometries.size() - 1)
        {
            simplified_geometry.pop_back();
        }
        overview_geometry.insert(overview_geometry.end(), simplified_geometry.begin(),
                                 simplified_geometry.end());
    }
    return overview_geometry;
}
}

std::vector<util::Coordinate> assembleOverview(const std::vector<LegGeometry> &leg_geometries,
                                               const bool use_simplification)
{
    if (use_simplification)
    {
        const auto zoom_level = calculateOverviewZoomLevel(leg_geometries);
        return simplifyGeometry(leg_geometries, zoom_level);
    }
    BOOST_ASSERT(!use_simplification);

    auto overview_size = std::accumulate(leg_geometries.begin(), leg_geometries.end(), 0,
                                         [](const std::size_t sum, const LegGeometry &leg_geometry)
                                         {
                                             return sum + leg_geometry.locations.size();
                                         }) -
                         leg_geometries.size() + 1;
    std::vector<util::Coordinate> overview_geometry;
    overview_geometry.reserve(overview_size);

    auto leg_index = 0UL;
    for (const auto geometry : leg_geometries)
    {
        auto begin = geometry.locations.begin();
        auto end = geometry.locations.end();
        if (leg_index < leg_geometries.size() - 1)
        {
            end = std::prev(end);
        }
        overview_geometry.insert(overview_geometry.end(), begin, end);
    }

    return overview_geometry;
}

} // namespace guidance
} // namespace engine
} // namespace osrm

#endif