HTML APIs

1- HTML5 Geolocation

The HTML Geolocation API is used to locate a user's position.

Locate the User's Position

The HTML Geolocation API is used to get the geographical position of a user.

Since this can compromise privacy, the position is not available unless the user approves it.

Browser Support

The numbers in the table specify the first browser version that fully supports Geolocation.

Note: Geolocation is much more accurate for devices with GPS, like iPhone.

Using HTML Geolocation

The getCurrentPosition() method is used to get the user's position.

The example below returns the latitude and longitude of the user's position:

Example

<script>
var x = document.getElementById("demo");
function getLocation() {
    if (navigator.geolocation) {
        navigator.geolocation.getCurrentPosition(showPosition);
    } else {
        x.innerHTML = "Geolocation is not supported by this browser.";
    }
}
function showPosition(position) {
    x.innerHTML = "Latitude: " + position.coords.latitude +
    "<br>Longitude: " + position.coords.longitude;
}
</script>

Example explained:

• Check if Geolocation is supported
• If supported, run the getCurrentPosition() method. If not, display a message to the user
• If the getCurrentPosition() method is successful, it returns a coordinates object to the function specified in the parameter (showPosition)
• The showPosition() function outputs the Latitude and Longitude

The example above is a very basic Geolocation script, with no error handling.

Handling Errors and Rejections

The second parameter of the getCurrentPosition() method is used to handle errors. It specifies a function to run if it fails to get the user's location:

Example

function showError(error) {
    switch(error.code) {
        case error.PERMISSION_DENIED:
            x.innerHTML = "User denied the request for Geolocation."
            break;
        case error.POSITION_UNAVAILABLE:
            x.innerHTML = "Location information is unavailable."
            break;
        case error.TIMEOUT:
            x.innerHTML = "The request to get user location timed out."
            break;
        case error.UNKNOWN_ERROR:
            x.innerHTML = "An unknown error occurred."
            break;
    }
}

Displaying the Result in a Map

To display the result in a map, you need access to a map service, like Google Maps.

In the example below, the returned latitude and longitude is used to show the location in a Google Map (using a static image):

Example

function showPosition(position) {
    var latlon = position.coords.latitude + "," + position.coords.longitude;

    var img_url = "http://maps.googleapis.com/maps/api/staticmap?center=
    "+latlon+"&zoom=14&size=400x300&sensor=false";

    document.getElementById("mapholder").innerHTML = "<img src='"+img_url+"'>";
}

How to show an interactive Google Map with a marker, zoom and drag options.

Location-specific Information

This page demonstrated how to show a user's position on a map.

Geolocation is also very useful for location-specific information, like:

• Up-to-date local information
• Showing Points-of-interest near the user
• Turn-by-turn navigation (GPS)

The getCurrentPosition() Method - Return Data

The getCurrentPosition() method returns an object if it is successful. The latitude, longitude and accuracy properties are always returned. The other properties are returned if available:

Property
Returns

coords.latitude
The latitude as a decimal number

coords.longitude
The longitude as a decimal number

coords.accuracy
The accuracy of position

coords.altitude
The altitude in meters above the mean sea level

coords.altitudeAccuracy
The altitude accuracy of position

coords.heading
The heading as degrees clockwise from North

coords.speed
The speed in meters per second

timestamp
The date/time of the response

Geolocation object - Other interesting Methods

watchPosition() - Returns the current position of the user and continues to return updated position as the user moves (like the GPS in a car).

clearWatch() - Stops the watchPosition() method.

The example below shows the watchPosition() method. You need an accurate GPS device to test this (like iPhone):

Example

<script>
var x = document.getElementById("demo");
function getLocation() {
    if (navigator.geolocation) {
        navigator.geolocation.watchPosition(showPosition);
    } else {
        x.innerHTML = "Geolocation is not supported by this browser.";
    }
}
function showPosition(position) {
    x.innerHTML = "Latitude: " + position.coords.latitude +
    "<br>Longitude: " + position.coords.longitude;
}
</script>