Calling Back: An Example for Google’s Geocoder Service and Custom Markers

I recently moved and naturally there was a lot of clothes which I do not need (read: do not fit in) any more. Throwing them away would be a waste and luckily, there is a social business called WAMS which (besides a lot of other nice projects) supports reuse and recycling. WAMS provides and maintains containers for collecting clothes on many locations in Tirol. Unfortunately, there is not yet a map available to find them easily. I took this as an opportunity for a little side project in Javascript. I am not affiliated with WAMS, but of course the code and data is open sourced here.

Idea

The idea was quite simple. I used some of the container addresses I found in the flyer and created a custom Google Map showing the locations of the containers. The final result looks like this and a live demo can be found at the Github page.

wams-markers

Retrieve Geolocation Information

The Google API allows to retrieve latitude and longitude data from any given address. If the address was found in Google’s database, the Server returns a GeocoderResult object containing the geometry information about the found object. This GeocoderGeometry contains the latitude and longitude data of the address. The first step retrieves the data from Google’s API by using the Geocoder class. To do so, the following JSON structure is iterated and the addresses are being fed to the Geocoding service.

            {
                "containerStandorte": [
                    {
                        "id": "1",
                        "name": "Pfarre Allerheiligen",
                        "address": "St.-Georgs-Weg 15, 6020, Innsbruck, Austria",
                        "latitude": "",
                        "longitude: "":
                    },
                    {
                        "id": "2",
                        "name": "Endhaltestelle 3er Linie Amras",
                        "address": "Philippine-Welser-Straße 49, 6020, Innsbruck, Austria",
                        "latitude": "",
                        "longitude": ""
            }

The Javascript code for obtaining the data is shown in the following listing:

window.onload = function() {

    // Data
    var wamsData =
 '{ "containerStandorte" : [' +
    '{ "id":"1", "name":"Pfarre Allerheiligen" , "address":"St.-Georgs-Weg 15, 6020, Innsbruck, Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"2", "name":"Endhaltestelle 3er Linie Amras" , "address":"Philippine-Welser-Straße 49, 6020, Innsbruck, Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"3", "name":"DEZ Einkaufszentrum Parkgarage" , "address":"Amraser-See-Straße 56a,6020 Innsbruck, Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"4", "name":"Wohnanlage Neue Heimat" , "address":"Geyrstraße 27-29, 6020 Innsbruck, Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"5", "name":"MPREIS Haller Straße" , "address":"Hallerstraße 212, 6020 Innsbruck, Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"6", "name":"Recyclinginsel Novapark" , "address":"Arzlerstraße 43, 6020 Innsbruck, Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"7", "name":"Höhenstraße / Hungerburg (neben Spar)" , "address":"Höhenstraße 125,6020 Innsbruck, 6020, Innsbruck, Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"8", "name":"Recyclinginsel Schneeburggasse" , "address":"Schneeburggasse 116, 6020 Innsbruck, Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"9", "name":"MPreis Fischerhäuslweg 31" , "address":"Fischerhäuslweg 31, 6020 Innsbruck, Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"10", "name":"Pfarre Petrus Canisius" , "address":"Santifallerstraße 5,6020 Innsbruck Austria" , "latitude":"", "longitude":"" },' +
    '{ "id":"11", "name":"MPreis Bachlechnerstraße" , "address":"Bachlechnerstraße 46, 6020 Innsbruck" , "latitude":"", "longitude":"" }'
    +' ]}';

    // Google Geocoder Library
    var geocoder = new google.maps.Geocoder();
    // Parse the JSON string into a javascript object.
    var wamsJSON = JSON.parse(wamsData);


    /**
        Iterate over containers and retrieve the geo location for their address.
    */
    function processContainers(){
        // Store amount of containers
        var amountOfContainers = wamsJSON.containerStandorte.length;
        // Iterate over all containers
        for (var i=0;i<amountOfContainers;i++){
            var container = wamsJSON.containerStandorte[i];
            // Encode the address of the container
            geocodeAddress(container, processContainerLocationCallback);
        };
    };

    /**
        Process the results
    */
    function processContainerLocationCallback(container,lat,long){
        wamsJSON = updateJSON(container,lat,long, printJSONCallback);
    }

    /**
        Update the JSON object and store the latitude and longitude information
    */
    function updateJSON(container,lat,long,printJSONCallback){
        // Store amount of containers
        var amountOfContainers = wamsJSON.containerStandorte.length;
        // Iterate over containers
        for (var i=0;i<amountOfContainers;i++){
            // Pick the correct id and store the data
            if(wamsJSON.containerStandorte[i].id==container.id){
                wamsJSON.containerStandorte[i].latitude=lat;
                wamsJSON.containerStandorte[i].longitude=long;
            }
        };
        // When the update is done, call the displayCallback
        printJSONCallback();
        return wamsJSON;
    };

    /*
        Google's Geocoder function takes and address as input and retrieves
        (among other data) the latitude and longitude of the provided address.
        Note that this is an asynchronous call, the response may take some time.
        Also remember that the processContainerLocationCallback which is given as
        an input parameter is just a variable. A variable which happens to be a function.

    */
    function geocodeAddress(container, processContainerLocationCallback){
        var address = container.address;
        geocoder.geocode( { 'address': address}, function(results, status) {
            // Anonymous function to process results.
            if (status == google.maps.GeocoderStatus.OK) {
                lat=results[0].geometry.location.lat();
                long=results[0].geometry.location.lng();
                // When the results have been retrieved,process them in the function processContainerLocationCallback
                processContainerLocationCallback(container, lat,long);
            } else {
                alert("Geocode was not successful for the following reason: " + status);
            }
        });
    };

    // Print the result
    function printJSONCallback(){
        var jsonString = JSON.stringify(wamsJSON, null,4);
        console.log(jsonString);
        document.getElementById("jsonOutput").innerHTML = jsonString;
    }

    // Start processing
    processContainers();
}

As the calls to the Google Services asynchronously, we need to use callbacks which are called when the function before has finished. Callbacks can be tricky and are a bit of a challenge to understand the first time. Especially the Google Geocoder methods require to work with several callbacks, which is often referred to as callback hell. The code above does the following things:

  1. Iterate over the JSON structure process each container individually -> function processContainers()
  2. For each container, call Google’s Geocoder and resolve the address to a location -> geocodeAddress(container, processContainerLocationCallback)
  3. After the result has been obtained, process the result. -> processContainerLocationCallback(container,lat,long)
  4. Update the JSON object by looping over all records and search for the correct id. Once the id was found, update latitude and longitude information. -> updateJSON(container,lat,long,printJSONCallback)
  5. Write the result to the Web page -> printJSONCallback()

The missing latitude and longitude values are retrieved and the JSON gets updated. The final result looks like this:

 
            {
                "containerStandorte": [
                    {
                        "id": "1",
                        "name": "Pfarre Allerheiligen",
                        "address": "St.-Georgs-Weg 15, 6020, Innsbruck, Austria",
                        "latitude": 47.2680316,
                        "longitude": 11.355563999999958
                    },
                    {
                        "id": "2",
                        "name": "Endhaltestelle 3er Linie Amras",
                        "address": "Philippine-Welser-Straße 49, 6020, Innsbruck, Austria",
                        "latitude": 47.2589929,
                        "longitude": 11.42600379999999
                    }
                    ...
            }

Now that we have the data ready, we can proceed with the second step.

Placing the Markers

I artistically created a custom marker image which we will use to indicate the location of a clothes container from WAMS.

wamsThis image replaces the Google standard marker. Now all that is left is that we iterate over the updated JSON object, which now contains also the latitude and longitude data and place a marker for each container. Note that hovering over the image displays the address of the container on the Map.

        // Data for container locations
        var wamsData = '{"containerStandorte":[{"id":"1","name":"Pfarre Allerheiligen",
"address":"St.-Georgs-Weg 15, 6020, Innsbruck, Austria","latitude":47.2680316,"longitude":11.355563999999958},
{"id":"2","name":"Endhaltestelle 3er Linie Amras","address":"Philippine-Welser-Straße 49, 6020, Innsbruck, Austria","latitude":47.2589929,"longitude":11.42600379999999},
{"id":"3","name":"DEZ Einkaufszentrum Parkgarage","address":"Amraser-See-Straße 56a,6020 Innsbruck, Austria","latitude":47.2625925,"longitude":11.430842299999995},
{"id":"4","name":"Wohnanlage Neue Heimat","address":"Geyrstraße 27-29, 6020 Innsbruck, Austria","latitude":47.2614899,"longitude":11.426765700000033},
{"id":"5","name":"MPREIS Haller Straße","address":"Hallerstraße 212, 6020 Innsbruck, Austria","latitude":47.2769524,"longitude":11.442559599999981},
{"id":"6","name":"Recyclinginsel Novapark","address":"Arzlerstraße 43, 6020 Innsbruck, Austria","latitude":47.2833947,"longitude":11.424273299999982},
{"id":"7","name":"Höhenstraße / Hungerburg (neben Spar)","address":"Höhenstraße 125,6020 Innsbruck, 6020, Innsbruck, Austria","latitude":47.2841353,"longitude":11.394666799999982},
{"id":"8","name":"Recyclinginsel Schneeburggasse","address":"Schneeburggasse 116, 6020 Innsbruck, Austria","latitude":47.2695889,"longitude":11.364059699999984},
{"id":"9","name":"MPreis Fischerhäuslweg 31","address":"Fischerhäuslweg 31, 6020 Innsbruck, Austria","latitude":47.261875,"longitude":11.364496700000018},
{"id":"10","name":"Pfarre Petrus Canisius","address":"Santifallerstraße 5,6020 Innsbruck Austria","latitude":47.2635626,"longitude":11.380990800000063},
{"id":"11","name":"MPreis Bachlechnerstraße","address":"Bachlechnerstraße 46, 6020 Innsbruck","latitude":47.2645067,"longitude":11.376220800000056}]}';


        function initialize() {
          var innsbruck = { lat: 47.2656733, lng: 11.3941983 };
          var map = new google.maps.Map(document.getElementById('map'), {
            zoom: 14,
            center: innsbruck
          });

          // Load Google Geocoder Library
          var geocoder = new google.maps.Geocoder();
          // Parse the data into a JSON
          var wamsJSON = JSON.parse(wamsData);
          // Iterate over all containers
          for(var i =0; i < wamsJSON.containerStandorte.length;i++){
              var container = wamsJSON.containerStandorte[i];
              placeMarkerOnMap(geocoder, map, container);
          };
        }

    // Custom marker
    var wamsLogo = {
      url: 'images/wams.png',
      // This marker is 20 pixels wide by 32 pixels high.
      size: new google.maps.Size(64, 64),
      // The origin for this image is (0, 0).
      origin: new google.maps.Point(0, 0),
      // The anchor for this image is the base of the flagpole at (0, 32).
      anchor: new google.maps.Point(64, 70)
    };

    // Define the shape for the marker
    var shape = {
      coords: [1, 1, 1, 64, 64, 64, 64, 1],
      type: 'poly'
    };

    // Place marker on the map
    function placeMarkerOnMap(geocoder, resultsMap, container) {
        // Create Google position object with latitude and longitude from the container object
        var positionLatLng = new google.maps.LatLng(parseFloat(container.latitude),parseFloat(container.longitude));
        // Create marker with the position, logo and address
        var marker = new google.maps.Marker({
          map: resultsMap,
          position: positionLatLng,
          icon: wamsLogo,
          shape: shape,
          title: container.address,
          animation: google.maps.Animation.DROP
        });
    }
    // Place marker on the map
    google.maps.event.addDomListener(window, 'load', initialize);

Hosting the Result

Github offers a great feature for hosting simple static Web pages. All is needed is a new orphan branch of your project, which is named gh-pages, as described here. This branch serves as the Web directory for all your files and allows to host Web pages for public projects for free. You can see the result of the project above here.

 

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