{Tutorial}HTML5 Geolocation.Step 28.

[MrHotFire]

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:

<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 "'>";
}

 

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):

<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>

 

Credits Olympus,Internet,ME.