c++ - 如何在 C++ BOOST 中加载像图形一样的 TIFF 图像

Question

我想在 boost C++ 中加载一个 tiff 图像(带有带浮点值的像素的 GEOTIFF)(我是 C++ 的新手)。我的目标是使用从源 A 到目标 B 的双向 Dijkstra 以获得更高的性能。

Boost:GIL load tiif images:
std::string filename( "raster_clip.tif" );
rgb8_image_t img;
read_image( filename, img, tiff_tag() ); 

但是如何转换为 Boost 图呢？我正在阅读文档并寻找示例，但我还没有能够实现它。

我发现的类似问题和例子:

Shortest path graph algorithm help Boost ;

http://www.geeksforgeeks.org/shortest-path-for-directed-acyclic-graphs/

我目前正在使用 scikit-image 库并使用 skimage.graph.route_through_array 函数在 python 中加载带有数组的图形。我使用 GDAL 通过加载图像获取数组，如本例中@ustroetz 所建议的那样 Here :

    raster = gdal.Open("raster.tiff")
    band = raster.GetRasterBand(1)
    array = band.ReadAsArray()

TIFF 示例(上传后已转换为 PNG)为:

Answer 1

好的，那么请阅读 PNG:

I've cropped the whitespace border since it wasn't consistent anyways

读取图像并采样

using Img = boost::gil::rgb8_image_t; // gray8_image_t;
using Px  = Img::value_type;

Img img;
//boost::gil::png_read_image("graph.png", img);
boost::gil::png_read_and_convert_image("graph.png", img);
auto vw = view(img);

接下来，确保我们知道尺寸以及如何处理每个单元格的中心像素:

double constexpr cell_w = 30.409;
double constexpr cell_h = 30.375;

auto pixel_sample = [=](boost::array<size_t, 2> xy) -> auto& {
    return vw((xy[0]+.5)*cell_w, (xy[1]+.5)*cell_h);
};

auto const w= static_cast<size_t>(img.dimensions()[0] / cell_w);
auto const h= static_cast<size_t>(img.dimensions()[1] / cell_h);

构建图

现在让我们制作图表。对于此任务，网格图似乎是有序的。它应该是 w×h 而不是在边缘环绕(如果应该，将 false 更改为 true):

using Graph = boost::grid_graph<2>;
Graph graph({{w,h}}, false);

我们想在每条边上附加权重。我们可以使用预先确定大小的老式外部属性映射:

std::vector<double> weight_v(num_edges(graph));
auto weights = boost::make_safe_iterator_property_map(weight_v.begin(), weight_v.size(), get(boost::edge_index, graph));

或者，我们可以使用动态分配和增长的属性映射:

auto weights = boost::make_vector_property_map<float>(get(boost::edge_index, graph));

作为奖励，下面是使用关联属性映射的等效方法:

std::map<Graph::edge_descriptor, double> weight_m;
auto weights = boost::make_assoc_property_map(weight_m);

其中每一个都是直接兼容的，选择权在您手中。

填充图形

我们简单地迭代所有边，根据颜色差异设置成本:

BGL_FORALL_EDGES(e, graph, Graph) {
    auto& from = pixel_sample(e.first);
    auto& to   = pixel_sample(e.second);

    // compare RED channels only
    auto cost = std::abs(from[0] - to[0]);
    put(weights, e, cost);
}

Note Consider normalizing weight to e.g. [0.0, 1.0) using the actual bit-depth of the source image

让我们创建一个验证 TIF，这样我们就可以实际看到样本在图像中的拍摄位置:

{
    BGL_FORALL_VERTICES(v, graph, Graph) {
        pixel_sample(v) = Px(255, 0, 123); // mark the center pixels so we can verify the sampling
    }

    boost::gil::tiff_write_view("/tmp/verification.tif", const_view(img));
}

verification.tif 最终如下(注意每个单元格的中心像素):

奖励:可视化网格图

让我们将其写入 Graphviz 文件:

{
    auto calc_color = [&](size_t v) {
        std::ostringstream oss;
        oss << std::hex << std::noshowbase << std::setfill('0');

        auto const& from = pixel_sample(vertex(v, graph));
        oss << "#" << std::setw(2) << static_cast<int>(from[0])
            << std::setw(2) << static_cast<int>(from[1])
            << std::setw(2) << static_cast<int>(from[2]);

        return oss.str();
    };

    write_dot_file(graph, weights, calc_color);
}

这从相同的样本像素计算颜色并使用一些 Graphviz 特定的魔法写入文件:

template <typename Graph, typename Weights, typename ColorFunction>
void write_dot_file(Graph const& graph, Weights const& weights, ColorFunction calc_color) {
    boost::dynamic_properties dp;
    dp.property("node_id",   get(boost::vertex_index, graph));
    dp.property("fillcolor", boost::make_transform_value_property_map(calc_color, get(boost::vertex_index, graph)));
    dp.property("style", boost::make_static_property_map<typename Graph::vertex_descriptor>(std::string("filled")));
    std::ofstream ofs("grid.dot");

    auto vpw = boost::dynamic_vertex_properties_writer { dp, "node_id" };
    auto epw = boost::make_label_writer(weights);
    auto gpw = boost::make_graph_attributes_writer(
            std::map<std::string, std::string> { },
            std::map<std::string, std::string> { {"shape", "rect"} },
            std::map<std::string, std::string> { }
        );

    boost::write_graphviz(ofs, graph, vpw, epw, gpw);
}

结果为 a grid.dot file like this .

接下来，让我们布局using neato :

neato -T png grid.dot -o grid.png

结果是:

完整代码 list

#include <boost/gil/extension/io/png_dynamic_io.hpp>
#include <boost/gil/extension/io/tiff_dynamic_io.hpp>
#include <boost/graph/grid_graph.hpp>
#include <boost/graph/iteration_macros.hpp>
#include <boost/graph/graphviz.hpp>
#include <iostream>

template <typename Graph, typename Weights, typename ColorFunction>
void write_dot_file(Graph const& graph, Weights const& weights, ColorFunction);

int main() try {
    using Img = boost::gil::rgb8_image_t; // gray8_image_t;
    using Px  = Img::value_type;

    Img img;
    //boost::gil::png_read_image("/home/sehe/graph.png", img);
    boost::gil::png_read_and_convert_image("/home/sehe/graph.png", img);
    auto vw = view(img);

    double constexpr cell_w = 30.409;
    double constexpr cell_h = 30.375;

    auto pixel_sample = [=](boost::array<size_t, 2> xy) -> auto& {
        return vw((xy[0]+.5)*cell_w, (xy[1]+.5)*cell_h);
    };

    auto const w= static_cast<size_t>(img.dimensions()[0] / cell_w);
    auto const h= static_cast<size_t>(img.dimensions()[1] / cell_h);

    using Graph = boost::grid_graph<2>;
    Graph graph({{w,h}}, false);

#if 0 // dynamic weight map
    auto weights = boost::make_vector_property_map<float>(get(boost::edge_index, graph));
    std::cout << "Edges: " << (weights.storage_end() - weights.storage_begin()) << "\n";

#elif 1 // fixed vector weight map
    std::vector<double> weight_v(num_edges(graph));
    auto weights = boost::make_safe_iterator_property_map(weight_v.begin(), weight_v.size(), get(boost::edge_index, graph));

#else // associative weight map
    std::map<Graph::edge_descriptor, double> weight_m;
    auto weights = boost::make_assoc_property_map(weight_m);
#endif

    auto debug_vertex = [] (auto& v) -> auto& { return std::cout << "{" << v[0] << "," << v[1] << "}"; };
    auto debug_edge   = [&](auto& e) -> auto& { debug_vertex(e.first) << " -> "; return debug_vertex(e.second); };

    BGL_FORALL_EDGES(e, graph, Graph) {
        //debug_edge(e) << "\n";
        auto& from = pixel_sample(e.first);
        auto& to   = pixel_sample(e.second);

        // compare RED channels only
        auto cost = std::abs(from[0] - to[0]);
        put(weights, e, cost);
    }

    {
        auto calc_color = [&](size_t v) {
            std::ostringstream oss;
            oss << std::hex << std::noshowbase << std::setfill('0');

            auto const& from = pixel_sample(vertex(v, graph));
            oss << "#" << std::setw(2) << static_cast<int>(from[0])
                << std::setw(2) << static_cast<int>(from[1])
                << std::setw(2) << static_cast<int>(from[2]);

            return oss.str();
        };

        write_dot_file(graph, weights, calc_color);
    }

    {
        BGL_FORALL_VERTICES(v, graph, Graph) {
            pixel_sample(v) = Px(255, 0, 123); // mark the center pixels so we can verify the sampling
        }

        boost::gil::tiff_write_view("/tmp/verification.tif", const_view(img));
    }

} catch(std::exception const& e) {
    std::cout << "Exception occured: " << e.what() << "\n";
}

template <typename Graph, typename Weights, typename ColorFunction>
void write_dot_file(Graph const& graph, Weights const& weights, ColorFunction calc_color) {
    boost::dynamic_properties dp;
    dp.property("node_id",   get(boost::vertex_index, graph));
    dp.property("fillcolor", boost::make_transform_value_property_map(calc_color, get(boost::vertex_index, graph)));
    dp.property("style", boost::make_static_property_map<typename Graph::vertex_descriptor>(std::string("filled")));
    std::ofstream ofs("grid.dot");

    auto vpw = boost::dynamic_vertex_properties_writer { dp, "node_id" };
    auto epw = boost::make_label_writer(weights);
    auto gpw = boost::make_graph_attributes_writer(
            std::map<std::string, std::string> { },
            std::map<std::string, std::string> { {"shape", "rect"} },
            std::map<std::string, std::string> { }
        );

    boost::write_graphviz(ofs, graph, vpw, epw, gpw);
}