Isochrone Explorer

A Node.js library for generating isochrones and finding routes using road network data and Dijkstra's algorithm.

This project enables you to:

• Generate isochrones to visualize areas reachable within a specified time or distance from a given point.
• Find the shortest route between two coordinates using road networks.

Isochrones represent areas accessible from a starting point within a given time or distance, supporting various travel modes (e.g., car, bike, walk, cycle).

Features

• Fetch road network data via API requests.
• Generate isochrones based on time or distance constraints.
• Calculate shortest paths between two points.
• Support for multiple travel modes: car, bike, walk, and cycle.
• Lightweight and dependency-efficient, using only axios for HTTP requests.

Prerequisites

Before getting started, ensure you have:

• Node.js (v14 or higher recommended)
• npm (v6 or higher)
• Internet access to fetch road network data via the API (no API key required)

Installation

Install the package via npm:

npm install isochrone-explorer

Dependencies

• axios (^1.6.0): For making HTTP requests to the API.

Code Examples

1. Generating Isochrones

Generate isochrones to determine areas reachable from a specific location within a given time or distance.

const { generateIsochrones } = require('isochrone-explorer');

async function generateIsochroneExample() {
  const locations = [[-122.4194, 37.7749]]; // [lon, lat] for San Francisco
  const distances = [5000]; // 5 km
  const times = [null]; // Use distance instead of time
  const modes = ['car'];

  try {
    const results = await generateIsochrones({ locations, distances, times, modes });
    console.log(results);
    // Output: [{ location: [-122.4194, 37.7749], polygon: [[lon1, lat1], [lon2, lat2], ...] }]
  } catch (error) {
    console.error('Error:', error.message);
  }
}

generateIsochroneExample();

Parameters:

• locations: Array of [lon, lat] coordinates.
• distances: Array of maximum distances (meters). Use null if using time.
• times: Array of maximum times (seconds). Use null if using distance.
• modes: Array of travel modes (car, bike, walk, cycle).

Output:

• Array of objects with:
  • location: Original [lon, lat] coordinates.
  • polygon: Array of [lon, lat] coordinates forming the isochrone boundary.

2. Finding Routes

Calculate the shortest path between two coordinates using road networks.

const { findRoute } = require('isochrone-explorer');

async function findRouteExample() {
  const startCoord = [-122.4194, 37.7749]; // San Francisco
  const endCoord = [-122.4089, 37.7837]; // Nearby point

  try {
    const path = await findRoute(startCoord, endCoord);
    console.log(path);
    // Output: [[lon1, lat1], [lon2, lat2], ...]
  } catch (error) {
    console.error('Error:', error.message);
  }
}

findRouteExample();

Parameters:

• startCoord: [lon, lat] of the starting point.
• endCoord: [lon, lat] of the destination.

Output:

• Array of [lon, lat] coordinates representing the shortest path, or an empty array if no path is found.

Configuration

Travel Modes

The package supports the following travel modes with default speeds (configurable in src/constants.js):

• car: 70 km/h
• bike: 45 km/h
• walk: 5 km/h
• cycle: 15 km/h

To customize speeds, modify src/constants.js:

module.exports = {
  MODE_SPEEDS: {
    car: 80, // Update to 80 km/h
    bike: 50,
    walk: 6,
    cycle: 20,
  },
};

Limitations

• Data Scope: Fetches road network data within a 1 km radius of the input coordinates, which may limit results for large isochrones or long routes.
• Polygon Output: Isochrone polygons are raw point sets and may require further processing for visualization (e.g., with Leaflet or Google Maps).
• Performance: Processing large road network datasets can be slow for extensive areas.
• API: Relies on an external API for fetching road network data, which may have rate limits or occasional downtime.

Integration with Map Libraries

To visualize isochrones or routes, you can integrate the output with mapping libraries like Leaflet or Google Maps.

Example: Isochrone with Leaflet

import React, { useEffect, useState } from 'react';
import { MapContainer, TileLayer, Polygon, Marker } from 'react-leaflet';
import { generateIsochrones } from 'isochrone-explorer';
import 'leaflet/dist/leaflet.css';

const IsochroneLeaflet = () => {
  const [isochrone, setIsochrone] = useState(null);
  const center = [37.7749, -122.4194]; // San Francisco [lat, lon]

  useEffect(() => {
    const fetchIsochrone = async () => {
      const results = await generateIsochrones({
        locations: [[-122.4194, 37.7749]], // [lon, lat]
        distances: [5000], // 5 km
        times: [null],
        modes: ['car'],
      });
      setIsochrone(results[0]?.polygon);
    };
    fetchIsochrone();
  }, []);

  return (
    <MapContainer center={center} zoom={13} style={{ height: '500px', width: '100%' }}>
      <TileLayer
        url="https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png"
        attribution='© OpenStreetMap contributors'
      />
      {isochrone && (
        <Polygon positions={isochrone.map(coord => [coord[1], coord[0]])} color="blue" fillOpacity={0.4} />
      )}
      <Marker position={center} />
    </MapContainer>
  );
};

export default IsochroneLeaflet;

Note: Requires react-leaflet and leaflet packages for visualization.

Contributing

Contributions are welcome! To contribute:

1. Fork the repository.
2. Create a feature branch (git checkout -b feature/your-feature).
3. Commit your changes (git commit -m 'Add your feature').
4. Push to the branch (git push origin feature/your-feature).
5. Open a pull request.

Author

Nihar Ranjan Mohanta