gallery_sankey_flow_diagram.cpp

This gallery example demonstrates creating a comprehensive Sankey diagram using Plotly.cpp to visualize energy flows from sources through sectors to end uses. Sankey diagrams excel at showing flow quantities and relationships in complex systems through proportional link widths.

Features demonstrated:

• Multi-stage flow visualization from sources to intermediate sectors to end uses
• Node categorization with color coding (sources, sectors, end uses)
• Proportional link width representing flow quantities
• Transparent link colors derived from source node colors
• Interactive hover information showing detailed flow data
• Custom node positioning and styling with thickness control
• Comprehensive energy system modeling with realistic flow relationships
• Professional layout with annotations and proper margins

Energy system components:

• Sources: Coal, Natural Gas, Nuclear, Hydro, Solar/Wind
• Sectors: Electricity Generation, Industrial, Transportation, Residential
• End Uses: Lighting, Heating, Manufacturing, Transportation

The diagram provides insights into energy distribution patterns, bottlenecks, and the relative importance of different pathways in the energy system.

Energy Flow Sankey Diagram

 
#include "plotly/plotly.hpp"
#include "utils/arg_parser.hpp"
#include <string>
#include <vector>
 
auto main(int argc, char *argv[]) -> int {
  // Parse command line arguments
  auto args = parseGalleryArgs(argc, argv);
 
  plotly::Figure fig;
  fig.openBrowser(args.headless);
 
  // Energy flow data - from sources to end uses
  std::vector<std::string> nodeLabels = {
      // Energy Sources (0-4)
      "Coal", "Natural Gas", "Nuclear", "Hydro", "Solar/Wind",
      // Energy Sectors (5-8)
      "Electricity Generation", "Industrial", "Transportation", "Residential",
      // End Uses (9-12)
      "Lighting", "Heating", "Manufacturing", "Transportation"};
 
  std::vector<std::string> nodeColors = {
      // Sources - darker colors
      "#8B4513", "#4169E1", "#FF4500", "#1E90FF", "#32CD32",
      // Sectors - medium colors
      "#FFD700", "#FF6347", "#9370DB", "#20B2AA",
      // End uses - lighter colors
      "#FFFF99", "#FFA07A", "#DDA0DD", "#98FB98"};
 
  // Define flow connections: [source_index, target_index, value]
  std::vector<int> sources = {
      // Sources to sectors
      0, 1, 2, 3, 4, // To Electricity Generation
      1, 0,          // To Industrial
      1,             // To Transportation
      1, 5,          // To Residential
      // Sectors to end uses
      5, 5, 8, // Electricity to Lighting, Heating, Residential
      6,       // Industrial to Manufacturing
      7,       // Transportation to Transportation
      8, 8     // Residential to Heating, Lighting
  };
 
  std::vector<int> targets = {
      // Sources to sectors
      5, 5, 5, 5, 5, // Coal, Gas, Nuclear, Hydro, Solar/Wind to Electricity
      6, 6,          // Gas, Coal to Industrial
      7,             // Gas to Transportation
      8, 8,          // Gas, Electricity to Residential
      // Sectors to end uses
      9, 10, 10, // Electricity to Lighting, Heating, Heating
      11,        // Industrial to Manufacturing
      12,        // Transportation to Transportation
      10, 9      // Residential to Heating, Lighting
  };
 
  std::vector<double> values = {
      // Sources to sectors (units: arbitrary energy units)
      35, 40, 20, 15, 10, // To Electricity Generation
      25, 15,             // To Industrial
      30,                 // To Transportation
      20, 50,             // To Residential
      // Sectors to end uses
      40, 30, 20, // From Electricity
      40,         // From Industrial
      30,         // From Transportation
      35, 35      // From Residential
  };
 
  // Create link colors with transparency
  std::vector<std::string> linkColors;
  for (int source : sources) {
    // Use source node color with transparency
    const std::string &baseColor = nodeColors[source];
    linkColors.push_back(baseColor + "80"); // Add 50% transparency
  }
 
  // Create Sankey trace
  plotly::Object trace = {
      {"type", "sankey"},
      {"orientation", "h"},
      {"node",
       {{"pad", 15},
        {"thickness", 20},
        {"line", {{"color", "black"}, {"width", 0.5}}},
        {"label", nodeLabels},
        {"color", nodeColors},
        {"hovertemplate", "%{label}<br>Total Flow: %{value}<extra></extra>"}}},
      {"link",
       {{"source", sources},
        {"target", targets},
        {"value", values},
        {"color", linkColors},
        {"hovertemplate",
         "Flow: %{source.label} → %{target.label}<br>" +
             std::string("Amount: %{value} units<extra></extra>")}}}};
 
  // Create layout
  plotly::Object layout = {
      {"title",
       {{"text", "Energy Flow Diagram<br>" +
                     std::string("<sub>From Sources to End Uses</sub>")},
        {"font", {{"size", 18}}}}},
      {"width", 1100},
      {"height", 700},
      {"margin", {{"l", 50}, {"r", 50}, {"t", 80}, {"b", 50}}},
      {"annotations",
       {{{"text", "Flow thickness represents energy quantity"},
         {"x", 0.5},
         {"y", -0.08},
         {"xref", "paper"},
         {"yref", "paper"},
         {"showarrow", false},
         {"font", {{"size", 12}}}}}}};
 
  // Create the plot
  std::vector<plotly::Object> data = {trace};
  fig.newPlot(data, layout);
 
  if (!args.headless) {
    fig.waitClose();
  } else {
    // Save image instead of opening browser
    plotly::Object imageOpts = {{"format", "png"},
                                {"width", 1100},
                                {"height", 700},
                                {"filename", "sankey_flow_diagram"}};
    fig.downloadImage(imageOpts);
  }
 
  return 0;
}