Finding Location with the Geolocation API - HTML5 Programming for ASP.NET Developers - page 306

The click event-handler function defines an options object with three settings: enableHighAccuracy ,
timeout , and maximumAge . This object specifies the options to be used by the getCurrentPosition() method.
The significance of these three options is described in Table 12-2.

Table 12-2. Options for the getCurrentPosition() Method

Option Description

enableHighAccuracy Boolean option that indicates whether to use the high-accuracy GPS technique to

find the user's location. A value of true indicates that GPS is to be used if available.
Of course, the device must have GPS support as well as the user's permission to
use this mode. Otherwise, this setting is ignored.

timeout

Indicates the number of milliseconds the web page should wait before giving up
location detection.

maximumAge Indicates how much old cached location data can be used. The value is in

milliseconds. The default is 0 , indicating that cached data is never used. You may
set this option if you wish to reduce the number of geolocation calls or save power.
However, the downside of setting maximumAge is that the location information can
be outdated, in which case the specified value may cause calculation errors.

The code in Listing 12-1 then calls the geolocation object's getCurrentPosition() method. This
method accepts three parameters: a success function that is called when the geolocation data is
successfully retrieved, an error function that is called if an error occurs while retrieving the geolocation
information, and the options object. Specifying the error function and options object is optional.
The OnSuccess() function that acts as a success callback is shown in Listing 12-2.

Listing 12-2. OnSuccess() Callback Function
function OnSuccess(position) {
var html = "";
html += "<tr><td>Latitude : </td>";
html += "<td>" + position.coords.latitude + "</td></tr>";
html += "<tr><td>Longitude : </td>";
html += "<td>" + position.coords.longitude + "</td></tr>";
html += "<tr><td>Accuracy : </td>";
html += "<td>" + position.coords.accuracy + "</td></tr>";
html += "<tr><td>Altitude : </td>";
html += "<td>" + position.coords.altitude + "</td></tr>";
html += "<tr><td>Altitude Accuracy : </td>";
html += "<td>" + position.coords.altitudeAccuracy + "</td></tr>";
html += "<tr><td>Heading : </td>";
html += "<td>" + position.coords.heading + "</td></tr>";
html += "<tr><td>Speed : </td>";
html += "<td>" + position.coords.speed + "</td></tr>";
html += "<tr><td>Timestamp : </td>";
html += "<td>" + new Date(position.timestamp).toString() + "</td></tr>";
$("#tblInfo").append(html);
}

OnSuccess() receives a position object that provides information about the user's location including
latitude and longitude. Most of these properties (except the timestamp) are available in the position
object's coords property. The pieces of information given by the position object are listed in Table 12-3.