turf.nearestPoint only returning the same point

问题

I am making a Leaflet map. I am loading some geoJSON data. I have an on click function for the map. When I click I simply want to alert the nearest point from the loaded geoJSON. The problem is that only one point is returned no matter where I click in the city ( the point shown in the image below.

//Create the map
var map = L.map('mapdiv').setView([-43.534384, 172.640528], 13);

// Add the basemap
L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
  attribution: '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'
}).addTo(map);

// Create a variable that is the URL of the schools data
var url = 'https://koordinates.com/services/query/v1/vector.json?key=8dcaa116555f4ef1bfae391119119bdc&layer=243&x=172.640565&y=-43.534366&max_results=100&radius=100000&geometry=true&with_field_names=true';

// Get the data from the service and asign it to a variable
function httpGet(theUrl) {
  var xmlHttp = new XMLHttpRequest();
  xmlHttp.open("GET", theUrl, false); // false for synchronous request
  xmlHttp.send(null);
  return xmlHttp.responseText;
}
var schoolData = JSON.parse(httpGet(url)).vectorQuery.layers[243];

// Set some options for styling the schools
var geojsonMarkerOptions = {
  radius: 8,
  fillColor: "#ff7800",
  color: "#000",
  weight: 1,
  opacity: 1,
  fillOpacity: 0.8
};

// Add the data to the map and add a popup from some wanted data
L.geoJSON(schoolData, {
  onEachFeature: function(feature, layer) {
    layer.bindPopup('<h3>' + feature.properties.NAME + '</h3><p><strong>Info:</strong> ' + feature.properties.TAGS + '</p>');
  }
}).addTo(map);

var points = turf.featureCollection(schoolData.features);

map.on('click', function(e) {
  var coord = e.latlng;
  var lat = coord.lat;
  var lng = coord.lng;
  var targetPoint = turf.point([lat, lng]);
  var nearest = turf.nearestPoint(targetPoint, points);
	alert(JSON.stringify(nearest));
});

html,
body {
  height: 100%;
}

#mapdiv {
  height: 100%;
}

<!DOCTYPE html>
<html>

  <head>
    <meta charset="UTF-8">
    <link rel="stylesheet" href="https://unpkg.com/leaflet@1.3.1/dist/leaflet.css" integrity="sha512-Rksm5RenBEKSKFjgI3a41vrjkw4EVPlJ3+OiI65vTjIdo9brlAacEuKOiQ5OFh7cOI1bkDwLqdLw3Zg0cRJAAQ==" crossorigin="" />
  </head>

  <body>
    <div id="mapdiv"></div>
  </body>
  <footer>
    <script src="https://unpkg.com/leaflet@1.3.1/dist/leaflet.js" integrity="sha512-/Nsx9X4HebavoBvEBuyp3I7od5tA0UzAxs+j83KgC8PU0kgB4XiK4Lfe4y4cgBtaRJQEIFCW+oC506aPT2L1zw==" crossorigin=""></script>
    <script src='https://npmcdn.com/@turf/turf/turf.min.js'></script>
  </footer>

</html>

回答1:

Posting the solution to help others in the future hopefully:

The problem I found was that Leaflet uses the format Latitude, Longitude for coordinates while Turf uses Longitude, Latitude. The reason the same point was returning was because the coordinates I was clicking at were getting flipped so I was getting the nearest of the points from 174.000, -43.000 instead of -43.000, 174.000. with a point So to fix this I simply changed the line

var targetPoint = turf.point([lat, lng]);

var targetPoint = turf.point([lng, lat]);

Working version below:

//Create the map
var map = L.map('mapdiv').setView([-43.534384, 172.640528], 13);

// Add the basemap
L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
  attribution: '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'
}).addTo(map);

// Create a variable that is the URL of the schools data
var url = 'https://koordinates.com/services/query/v1/vector.json?key=8dcaa116555f4ef1bfae391119119bdc&layer=243&x=172.640565&y=-43.534366&max_results=100&radius=100000&geometry=true&with_field_names=true';

// Get the data from the service and asign it to a variable
function httpGet(theUrl) {
  var xmlHttp = new XMLHttpRequest();
  xmlHttp.open("GET", theUrl, false); // false for synchronous request
  xmlHttp.send(null);
  return xmlHttp.responseText;
}
var schoolData = JSON.parse(httpGet(url)).vectorQuery.layers[243];

// Set some options for styling the schools
var geojsonMarkerOptions = {
  radius: 8,
  fillColor: "#ff7800",
  color: "#000",
  weight: 1,
  opacity: 1,
  fillOpacity: 0.8
};

// Add the data to the map and add a popup from some wanted data
L.geoJSON(schoolData, {
  onEachFeature: function(feature, layer) {
    layer.bindPopup('<h3>' + feature.properties.NAME + '</h3><p><strong>Info:</strong> ' + feature.properties.TAGS + '</p>');
  }
}).addTo(map);

var points = turf.featureCollection(schoolData.features);

map.on('click', function(e) {
  var coord = e.latlng;
  var lat = coord.lat;
  var lng = coord.lng;
  var targetPoint = turf.point([lng, lat]);
  var nearest = turf.nearestPoint(targetPoint, points);
	alert(JSON.stringify(nearest));
});

html,
body {
  height: 100%;
}

#mapdiv {
  height: 100%;
}

<!DOCTYPE html>
<html>

  <head>
    <meta charset="UTF-8">
    <link rel="stylesheet" href="https://unpkg.com/leaflet@1.3.1/dist/leaflet.css" integrity="sha512-Rksm5RenBEKSKFjgI3a41vrjkw4EVPlJ3+OiI65vTjIdo9brlAacEuKOiQ5OFh7cOI1bkDwLqdLw3Zg0cRJAAQ==" crossorigin="" />
  </head>

  <body>
    <div id="mapdiv"></div>
  </body>
  <footer>
    <script src="https://unpkg.com/leaflet@1.3.1/dist/leaflet.js" integrity="sha512-/Nsx9X4HebavoBvEBuyp3I7od5tA0UzAxs+j83KgC8PU0kgB4XiK4Lfe4y4cgBtaRJQEIFCW+oC506aPT2L1zw==" crossorigin=""></script>
    <script src='https://npmcdn.com/@turf/turf/turf.min.js'></script>
  </footer>

</html>

来源：https://stackoverflow.com/questions/50399406/turf-nearestpoint-only-returning-the-same-point

标签

javascript

leaflet

geojson

turfjs