isochrone-explorer/src/isochrone.js

A powerful isochrone and routing engine based on Dijkstra's algorithm for accurate travel time calculations.

const { getOsmData } = require('./osm/overpass');
const { parseGraph, findClosestNode } = require('./utils/osmUtils');
const { dijkstra } = require('./utils/dijkstra');
const { reducePointsToPolygon } = require('./utils/geoUtils');
const { MODE_SPEEDS } = require('./constants');

async function generateIsochrones({ locations, distances, times, modes }) {
  const results = [];

  for (let i = 0; i < locations.length; i++) {
    const [lon, lat] = locations[i];
    const mode = modes[i];

    if (!MODE_SPEEDS[mode]) {
      results.push({ error: `Invalid mode: ${mode}` });
      continue;
    }

    const osmData = await getOsmData(lat, lon);
    const { graph, nodeCoords } = parseGraph(osmData);
    const startNode = findClosestNode(nodeCoords, lat, lon);
    if (!startNode) {
      results.push({ error: "No start node found" });
      continue;
    }

    const reachableNodes = dijkstra(
      graph,
      startNode,
      distances[i] || null,
      times[i] || null,
      nodeCoords,
      mode,
      distances[i] ? "distance" : "time"
    );

    const coords = reachableNodes.map(n => [nodeCoords[n].lat, nodeCoords[n].lon]);
    const polygon = reducePointsToPolygon(coords);
    results.push({ location: locations[i], polygon });
  }

  return results;
}

module.exports = { generateIsochrones };