Wednesday, September 17, 2014

Hi, in this post I will explain how to develop a simple web application with Leaflet.js where device locations will be updated real-time and I will add quite a few extra features to the UI as well :)

What is Leaflet.js


"Leaflet is a modern open-source JavaScript library for mobile-friendly interactive maps. It is developed by Vladimir Agafonkin with a team of dedicated contributors. Weighing just about 33 KB of JS, it has all the features most developers ever need for online maps."


Functions that are included in the application.

  1. Ability to switch Maps.
  2. Updating device location real-time.
  3. Drawing the route when the device is moving.
  4. Clearing layers and routes.
  5. Hiding different layers.
  6. Resetting the Map
  7. Maintaining the focus on a specific marker.

I will add everything in a simple HTML page, There won't be any themes so it won't look pretty.

Downloading and setting up of leaflet is pretty straight forward, its all well documented here.

In order to demonstrate marker movements I have written a small JavaScript to generate coordinates and device IDs.

So lets get started. :)

The following folder structure will be followed when storing the resources.



So lets create a new html file called index.html

Add the following code to the file.

I have explain the codes snippets within the code it self via comments.



<!DOCTYPE html>
<html>

<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">

<title>Real Time Updating Map</title>

<!-- Addning Leaflet Style Sheets -->
<link rel="stylesheet" href="CSS/leaflet.css" />

</head>

<body style="background-color: white;">

 <div id="wrapper" style="background-color: #EBD6EB;">
  <div id="page-wrapper">
   Display Settings

   <li>Draw Paths : &nbsp;&nbsp;</a> <input id="drawPath"
    type="checkbox" name="drawPath">
    <button type="button" onclick="checkCheckBox();">DRAW</button>
   </li>
   <li><a style="text-decoration: none">Clear All Paths :
     &nbsp;&nbsp;</a>
    <button type="button" onclick="clearMarkers();">CLEAR</button></li>

   <li>Focuss on a Device : <input id="followID"
    class="form-control" placeholder="Enter ID"> <input
    id="followId" type="checkbox" name="drawPath" disabled="disabled">

    <button type="button" onclick="followID(); checkBoxFollow();">Follow</button></li>
   <li>Reset Map : &nbsp;&nbsp;
    <button type="button" onclick="resetMap();">Reset</button>

   </li>
  </div>

 </div>

 <div align="center" style="padding: 0px">
  <div id="map" style="width: 1100px; height: 600px"></div>
 </div>

 <h4>Connected Device IDs</h4>
 <textarea class="form-control" id="idListArea" readonly></textarea>
 <h4>Output Console</h4>

 <textarea id="messagesTextArea" rows="17" cols="150" readonly></textarea>

 <br>

 <button type="button" onclick="messagesTextArea.value=null;">Clear
  Console</button>

 <!-- Adding the leaflet JS -->
 <script src="JS/leaflet.js"></script>

 <script>
  //Creating a Layers for the markers and Polylines and Creating the Main map
  var markerLayer = new L.layerGroup();
  var polylineLayer = new L.layerGroup();

  var mbAttr = 'Map data &copy; <a href="http://openstreetmap.org">OpenStreetMap</a> contributors, '
    + '<a href="http://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>, '
    + 'Imagery © <a href="http://mapbox.com">Mapbox</a>', mbUrl = 'https://{s}.tiles.mapbox.com/v3/{id}/{z}/{x}/{y}.png';

  var grayscale = L.tileLayer(mbUrl, {
   id : 'examples.map-20v6611k',
   attribution : mbAttr
  }), streets = L.tileLayer(mbUrl, {
   id : 'examples.map-i86knfo3',
   attribution : mbAttr
  });

  var map = L.map('map', {
   center : [ 6.88869, 79.85878 ],
   zoom : 13,
   layers : [ streets, markerLayer, polylineLayer ]
  });

  var baseLayers = {
   "Grayscale" : grayscale,
   "Streets" : streets
  };

  var overlays = {
   "Marker Layer" : markerLayer,
   "Path Layer" : polylineLayer
  };

  L.control.layers(baseLayers, overlays).addTo(map);
 </script>

 <script type="text/javascript">
  // This script is to simmulate a dataset to demonstrate 
  var j = 0;
  var lat = 6.88869;
  var lon = 79.85878;
  var speedflag = "false";

  function myLoop() {
   setTimeout(function() {

    lat = lat + 0.0001;
    lon = lon + 0.0001;

    lat2 = lat + 0.0001;
    lon2 = lon + 0.0002;

    var id = Math.floor((Math.random() * 2) + 1);

    mapUpdater("" + id, lat, lon);

    j++;
    if (j < 1000) {
     myLoop();
    }
   }, 500)
  }

  myLoop();
 </script>

 <script type="text/javascript">
  //Marker Icon List Class
  var markers = L.Icon.extend({
   options : {
    shadowUrl : 'images/marker-shadow.png',

    iconSize : [ 41, 41 ],
    shadowSize : [ 41, 41 ],
    iconAnchor : [ 20, 40 ],
    shadowAnchor : [ 10, 40 ],
    popupAnchor : [ 0, -30 ]
   }
  });

  var defIcon = L.Icon.Default.extend({
   options : {
    iconUrl : 'images/marker-icon.png'
   }
  });
 </script>

 <script type="text/javascript">
  //Main Map Related Scripts
  var idList = [];

  function checkCheckBox() {

   var check = document.getElementById("drawPath");
   if (check.checked == true) {
    check.checked = false;
   } else {
    check.checked = true;
   }
  }

  function mapUpdater(id, lat, lon) {

   var proxi = true;
   var len = null;
   var poly = null;
   var mark = null;

   //If the list doesn't contain anything Adding The Markers and PolyLines
   if (idList.length == 0) {

    mark = L.marker([ lat, lon ]).bindPopup("Vehicle ID : " + id, {
     autoPan : false
    });
    markerLayer.addLayer(mark);
    poly = L.polyline([], {
     color : 'green'
    });
    polylineLayer.addLayer(poly).addTo(map);

    idList.push([ id, mark, poly, false ]);

    idListArea.value += id + ", ";
    return;
   }

   for (var i = idList.length; i > 0; i--) {

    if (id == idList[i - 1][0]) {
     len = i - 1;
     break;
    }
    // If the ID is not in the list initiate new entry
    else if ((i - 1) == 0) {

     mark = L.marker([ lat, lon ]).bindPopup(
       "Vehicle ID : " + id, {
        autoPan : false
       });
     markerLayer.addLayer(mark);
     poly = L.polyline([], {
      color : 'green'
     });
     polylineLayer.addLayer(poly).addTo(map);
     len = idList.length - 1;

     idList.push([ id, mark, poly, false ]);
     idListArea.value += id + ", ";
     return;
    }
   }

   if (idList[len][3] == true) {
    idList[i - 1][2].addLatLng([ lat, lon ]);
    poly = L.polyline([], {
     color : 'Green'
    });
    polylineLayer.addLayer(poly).addTo(map);
    idList[len][2] = poly;
    idList[len][3] = false;
   }

   idList[len][1].setLatLng([ lat, lon ]).update(); // updating the marker

   // Drawing the Path if the check box is checked
   if (document.getElementById('drawPath').checked) {
    idList[len][2].addLatLng([ lat, lon ]); // updating the poly-line
   }

   // Maintaining the focus on a selected device
   if (document.getElementById("followId").checked
     && document.getElementById("followID").value == id) {
    map.panTo([ lat, lon ], {
     duration : 0.5
    });
   }

   //Updating the Output Console
   messagesTextArea.value += "ID : " + id + " Longtitute : " + lon
     + " Latitude : " + lat + "\n";
   var textarea = document.getElementById('messagesTextArea');
   textarea.scrollTop = textarea.scrollHeight;

  }

  // Function too Clear all the markers from the map
  function clearMarkers() {

   polylineLayer.clearLayers();

   for (var i = idList.length; i > 0; i--) { // Re adding the polylines since clear Layers remove all the objects
    poly = L.polyline([], {
     color : 'green'
    });
    polylineLayer.addLayer(poly).addTo(map);
    idList[i - 1][2] = poly;
   }
  }

  //Function to maintain focuss on a device
  function followID() {
   var id = document.getElementById("followID").value;
   if (id != "") {
    for (var i = idList.length; i > 0; i--) {
     if (idList[i - 1][0] == id) {
      idList[i - 1][1].openPopup();
      break;
     }
    }
   }
  }

  //toggling the check box
  function checkBoxFollow() {
   var fid = document.getElementById("followID").value;
   var checkbox = document.getElementById("followId");

   if (fid != "") {

    if (checkbox.checked) {
     checkbox.checked = false;
    } else {
     checkbox.checked = true;
    }
   }
  }

  // Function to Reset the Map
  function resetMap() {
   polylineLayer.clearLayers();
   markerLayer.clearLayers();
   idList.length = 0;
   idListArea.value = "";
  }
 </script>
</body>
</html>


Now in the folders I have mentioned above add necessary resources. leaflet JS/CSS files. Marker images etc. You can find everything from the following Git Repo as well.

https://github.com/ycrnet/Real_Time_Updating_Map

Just clone the above repository and you can find everything in it.

The Final output will look like following



As you can see, you can play around with the top control panel. It will provide all the added functionality I have mentioned above.

This project was done for a different integration and the UI was updated with web-sockets. You can Find the details about the project from here.

Hope this post will help someone interested. Thanks for reading and drop a comment if you have any Queries :)

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