Google Maps原型开发：如何获取Wonderland Trail的经纬度坐标？

Hey there! Let's break down why the Roads API wasn't working for you and how to grab that coordinate sequence for the Wonderland Trail you need.

Why Roads API Returned Empty Responses #

Your observation about the roads.arterial label visibility affecting the trail's display is totally correct—Google Maps does categorize the Wonderland Trail under the roads.arterial feature type for rendering. However, the Roads API (snapToRoad and nearestRoads endpoints) is built specifically for motor vehicle-accessible roads. Since the Wonderland Trail is a hiking path, it’s not included in the Roads API’s dataset, which explains the empty responses you received.

Reliable Ways to Retrieve the Trail's Coordinates #

Here are the best methods to get the full latitude/longitude sequence for the trail:

1. Use the Places API #

The Wonderland Trail is a well-known landmark, so it’s indexed in Google’s Places database. Follow these steps:

• Step 1: Get the Place ID
  Use the Text Search endpoint to locate the trail and grab its unique place_id:

  curl "https://maps.googleapis.com/maps/api/place/textsearch/json?query=Wonderland Trail&key=YOUR_API_KEY"
  

  Look for the top result matching the Wonderland Trail and note its place_id.

• Step 2: Fetch the Trail's Geometry
  Pass the place_id to the Places Details endpoint, requesting the geometry field. The response will include an encoded polyline representing the trail’s path:

  curl "https://maps.googleapis.com/maps/api/place/details/json?place_id=YOUR_PLACE_ID&fields=geometry&key=YOUR_API_KEY"
  

• Step 3: Decode the Polyline
  Convert the encoded string into a readable coordinate sequence. In JavaScript, use the Maps JavaScript API’s built-in utility:

  const encodedPolyline = "YOUR_ENCODED_POLYLINE_STRING";
  const coordinates = google.maps.geometry.encoding.decodePath(encodedPolyline);
  // coordinates will be an array of LatLng objects with lat/lng values
  

2. Use the Directions API (For Partial/Full Routes) #

If the Places API doesn’t return the full trail polyline, use the Directions API by setting start/end points at key trail locations (since it’s a loop, split it into segments if needed):

curl "https://maps.googleapis.com/maps/api/directions/json?origin=Wonderland Trail Trailhead&destination=Wonderland Trail Loop End&travelmode=walking&key=YOUR_API_KEY"

The response includes overview_polyline and legs.steps with detailed coordinate data for the route.

3. Static Export from Google My Maps #

If you don’t need dynamic retrieval in your app:

• Open Google My Maps, search for the Wonderland Trail, and add it to your map.
• Export the map as a KML or GPX file.
• Parse the file using libraries like fastkml (Python) or @tmcw/togeojson (JavaScript) to extract the full coordinate sequence.

Final Tips #

Not all trails have fully indexed geometry in the Places API, so if the first method falls short, combine it with the Directions API or a static export. Also, ensure your API key has the necessary APIs (Places, Directions) enabled in the Google Cloud Console.

内容的提问来源于stack exchange，提问作者Brian Quinn