Google Maps Directions API：如何实现Android isLocationOnPath路径点位判断功能？

Absolutely! You can replicate Android's isLocationOnPath functionality using data from the Google Maps Directions API. Here's a step-by-step guide to implement this in your Node.js code:

First, you need to pull the encoded polyline from the Directions API response. This polyline represents the full route path (you can use the overview_polyline for the entire route, or individual step polylines for more granularity).

Android's isLocationOnPath works by checking if the shortest distance from a target point to any segment of the route is within a specified tolerance (in meters). We'll replicate this with three key parts:

• Decoding the polyline into geographic coordinates
• Calculating the shortest distance from the target point to the route segments
• Comparing that distance to your tolerance threshold

Here's how to integrate this into your existing code:

const googleMapsClient = require('@google/maps').createClient({ key: 'KEY' });

googleMapsClient.directions({ 
  origin: 'Bangalore, Karnataka', 
  destination: 'Mumbai, Maharathra', 
  mode: "driving", 
}, function(err, response) { 
  if (!err) {
    // Extract the encoded polyline for the route
    const encodedPolyline = response.json.routes[0].overview_polyline.points;
    // Decode into an array of [lat, lng] pairs
    const routePath = decodePolyline(encodedPolyline);
    
    // Example target location to check (replace with your coordinates)
    const targetLocation = [17.4123, 78.5432];
    // Tolerance in meters (matches Android's tolerance parameter)
    const tolerance = 50; // 50 meters
    
    // Check if the location is on the path
    const isOnPath = isLocationOnPath(targetLocation, routePath, tolerance);
    console.log("Is location on route?", isOnPath);
  } else {
    console.error("ERR", err);
  }
});

// Decodes Google's encoded polyline string into [lat, lng] pairs
function decodePolyline(encoded) {
  const points = [];
  let index = 0, len = encoded.length;
  let lat = 0, lng = 0;

  while (index < len) {
    let b, shift = 0, result = 0;
    do {
      b = encoded.charCodeAt(index++) - 63;
      result |= (b & 0x1f) << shift;
      shift += 5;
    } while (b >= 0x20);
    const dlat = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
    lat += dlat;

    shift = 0;
    result = 0;
    do {
      b = encoded.charCodeAt(index++) - 63;
      result |= (b & 0x1f) << shift;
      shift += 5;
    } while (b >= 0x20);
    const dlng = ((result & 1) != 0 ? ~(result >> 1) : (result >> 1));
    lng += dlng;

    points.push([lat / 1e5, lng / 1e5]);
  }
  return points;
}

// Checks if target point is within tolerance of the route path
function isLocationOnPath(target, path, tolerance) {
  if (path.length < 2) return false; // Need at least two points for a valid path

  let minDistance = Infinity;

  // Check distance to each segment in the path
  for (let i = 0; i < path.length - 1; i++) {
    const segmentStart = path[i];
    const segmentEnd = path[i + 1];
    const distance = distanceToSegment(target, segmentStart, segmentEnd);
    
    minDistance = Math.min(minDistance, distance);
    // Early exit if we find a segment within tolerance
    if (minDistance <= tolerance) return true;
  }

  return minDistance <= tolerance;
}

// Calculates shortest distance from point to a line segment (spherical coordinates)
function distanceToSegment(p, a, b) {
  const distPA = haversineDistance(p, a);
  const distPB = haversineDistance(p, b);
  const distAB = haversineDistance(a, b);

  if (distAB === 0) return distPA; // Segment is a single point

  // Calculate projection of point onto the segment
  const t = Math.max(0, Math.min(1, ((distPA * distPA - distPB * distPB + distAB * distAB) / (2 * distAB))));
  const projLat = a[0] + t * (b[0] - a[0]);
  const projLng = a[1] + t * (b[1] - a[1]);

  return haversineDistance(p, [projLat, projLng]);
}

// Haversine formula to calculate distance between two geographic points (meters)
function haversineDistance(p1, p2) {
  const earthRadius = 6371000; // Meters
  const dLat = toRadians(p2[0] - p1[0]);
  const dLng = toRadians(p2[1] - p1[1]);
  const lat1 = toRadians(p1[0]);
  const lat2 = toRadians(p2[0]);

  const a = Math.sin(dLat/2) * Math.sin(dLat/2) +
            Math.sin(dLng/2) * Math.sin(dLng/2) * Math.cos(lat1) * Math.cos(lat2);
  const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
  return earthRadius * c;
}

// Helper to convert degrees to radians
function toRadians(degrees) {
  return degrees * (Math.PI / 180);
}

• The decodePolyline function converts the API's encoded string into usable latitude/longitude pairs.
• We use the Haversine formula to calculate distances between geographic points, since we're working on a spherical Earth (not a flat plane).
• The tolerance parameter works exactly like Android's: it defines how close the target point needs to be to the route (in meters) to be considered "on the path".

内容的提问来源于stack exchange，提问作者Sunil Kumar