HTML5 Geolocation - Locate the User's Position - Handling Errors and Rejections

Locate the User's Position

The HTML5 Geolocation API is used to get the geographical position of a user.

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

Browser Support

Internet Explorer 9, Firefox, Chrome, Safari and Opera support Geolocation.
Note: Geolocation is much more accurate for devices with GPS, like iPhone

HTML5 - Using Geolocation

Use the getCurrentPosition() method to get the user's position.
The example below is a simple Geolocation example returning 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 gets the displays 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:

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;
    }
  }


Error Codes:

• Permission denied - The user did not allow Geolocation
• Position unavailable - It is not possible to get the current location
•  Timeout - The operation timed out

Displaying the Result in a Map

To display the result in a map, you need access to a map service that can use latitude and longitude, like Google Maps:

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+"' />";
}

In the example above we use the returned latitude and longitude data to show the location in a Google map (using a static image).
How to use a script to show an interactive map with a marker, zoom and drag options.

Location-specific Information

This page demonstrated how to show a user's position on a map. However, Geolocation is also very useful for location-specific information.
Examples:

• 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 below are returned if available.

Property	Description
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>

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