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HTML5 Guide (4) - Detailed explanation of using Geolocation

黄舟Original: 2017-03-22 16:09:341669browse

What we are going to learn today is to use Geolocation to implement positioning functions. We can obtain the Geolocation object through navigator.geolocation, which provides the following methods:

getCurrentPosition(callback,errorCallback,options): Get the current position;

watchPosition(callback,error,options): Start monitoring the current location;

clearWatch(id): Stop monitoring the current location.

Note: The browser used in the example below is chrome. If you use other browsers, I cannot guarantee that the running results will be consistent with the results displayed in the example.

　1. Get the current position

　We will use the getCurrentPosition method to obtain the current position. The location information will not be returned directly in the form of a result. We Need to use callback function for processing. There will be some delays in getting the coordinates, and you will be asked for access permissions. Let's look at the following example:

<!DOCTYPE HTML><html><head>
    <title>Example</title>
    <style>
        table{border-collapse: collapse;}
        th, td{padding: 4px;}
        th{text-align: right;}
    </style></head><body>
    <table border="1">
        <tr>
            <th>Longitude:</th>
            <td id="longitude">-</td>
            <th>Latitude:</th>
            <td id="latitude">-</td>
        </tr>
        <tr>
            <th>Altitude:</th>
            <td id="altitude">-</td>
            <th>Accuracy:</th>
            <td id="accuracy">-</td>
        </tr>
        <tr>
            <th>Altitude Accuracy:</th>
            <td id="altitudeAccuracy">-</td>
            <th>Heading:</th>
            <td id="heading">-</td>
        </tr>
        <tr>
            <th>Speed:</th>
            <td id="speed">-</td>
            <th>Time Stamp:</th>
            <td id="timestamp">-</td>
        </tr>
    </table>
    <script>
        navigator.geolocation.getCurrentPosition(displayPosition);        
        function displayPosition(pos) {            
        var properties = [&#39;longitude&#39;, &#39;latitude&#39;, &#39;altitude&#39;, &#39;accuracy&#39;, &#39;altitudeAccuracy&#39;, &#39;heading&#39;, &#39;speed&#39;];            
        for (var i = 0, len = properties.length; i < len; i++) {                
        var value = pos.coords[properties[i]];
                document.getElementById(properties[i]).innerHTML = value;
               
            }
            document.getElementById(&#39;timestamp&#39;).innerHTML = pos.timestamp;
        }    </script></body></html>

The returned position object contains two attributes, coords: returns coordinate information; timestamp: the time when coordinate information was obtained. Among them, coords includes the following attributes: latitude: latitude; longitude: longitude; altitude: height; accuracy: accuracy (meters); altitudeAccuracy: altitude accuracy (meters); heading: direction of travel; speed: speed of travel (meters/second) .

Not all information will be returned, depending on the device you are hosting your browser on. Mobile devices with GPS, accelerometer, and compass will return most of the information, but home computers will not. The location information obtained by the home computer depends on the network environment or wifi. Let's look at the results of the above example.

Click Allow to obtain coordinate information.

2. Handling exceptions

Now we introduce the

Exception handling of getCurrentPosition, which is done by using errorCallback Callback function implemented. The parameter error returned by the function contains two attributes, code: error type code; message: error message. The code contains three values: 1: The user is not authorized to use geolocation; 2: Unable to obtain coordinate information; 3: Timeout for obtaining information.

Let’s look at an example:

<!DOCTYPE HTML><html><head>
    <title>Example</title>
    <style>
        table{border-collapse: collapse;}
        th, td{padding: 4px;}
        th{text-align: right;}
    </style></head><body>
    <table border="1">
        <tr>
            <th>Longitude:</th>
            <td id="longitude">-</td>
            <th>Latitude:</th>
            <td id="latitude">-</td>
        </tr>
        <tr>
            <th>Altitude:</th>
            <td id="altitude">-</td>
            <th>Accuracy:</th>
            <td id="accuracy">-</td>
        </tr>
        <tr>
            <th>Altitude Accuracy:</th>
            <td id="altitudeAccuracy">-</td>
            <th>Heading:</th>
            <td id="heading">-</td>
        </tr>
        <tr>
            <th>Speed:</th>
            <td id="speed">-</td>
            <th>Time Stamp:</th>
            <td id="timestamp">-</td>
        </tr>
        <tr>
            <th>Error Code:</th>
            <td id="errcode">-</td>
            <th>Error Message:</th>
            <td id="errmessage">-</td>
        </tr>
    </table>
    <script>
        navigator.geolocation.getCurrentPosition(displayPosition, handleError);        
        function displayPosition(pos) {            
        var properties = ["longitude", "latitude", "altitude", "accuracy", "altitudeAccuracy", "heading", "speed"];            
        for (var i = 0; i < properties.length; i++) {                
        var value = pos.coords[properties[i]];
                document.getElementById(properties[i]).innerHTML = value;
            }
            document.getElementById("timestamp").innerHTML = pos.timestamp;
        }        function handleError(err) {
            document.getElementById("errcode").innerHTML = err.code;
            document.getElementById("errmessage").innerHTML = err.message;
        }    </script></body></html>

Authorization denied, running result:

3 .Use geolocation optional parameter items

The options in getCurrentPosition(callback,errorCallback,options) have the following parameters that can be used, enableHighAccuracy: use the best effect; timeout: timeout time (milliseconds); maximumAge : Specifies the

cache time (milliseconds). Let’s take the following example:

<!DOCTYPE HTML><html><head>
    <title>Example</title>
    <style>
        table{border-collapse: collapse;}
        th, td{padding: 4px;}
        th{text-align: right;}
    </style></head><body>
    <table border="1">
        <tr>
            <th>Longitude:</th>
            <td id="longitude">-</td>
            <th>Latitude:</th>
            <td id="latitude">-</td>
        </tr>
        <tr>
            <th>Altitude:</th>
            <td id="altitude">-</td>
            <th>Accuracy:</th>
            <td id="accuracy">-</td>
        </tr>
        <tr>
            <th>Altitude Accuracy:</th>
            <td id="altitudeAccuracy">-</td>
            <th>Heading:</th>
            <td id="heading">-</td>
        </tr>
        <tr>
            <th>Speed:</th>
            <td id="speed">-</td>
            <th>Time Stamp:</th>
            <td id="timestamp">-</td>
        </tr>
        <tr>
            <th>Error Code:</th>
            <td id="errcode">-</td>
            <th>Error Message:</th>
            <td id="errmessage">-</td>
        </tr>
    </table>
    <script>
        var options = {
            enableHighAccuracy: false,
            timeout: 2000,
            maximumAge: 30000
        };
        navigator.geolocation.getCurrentPosition(displayPosition, handleError, options);        
        function displayPosition(pos) {            
        var properties = ["longitude", "latitude", "altitude", "accuracy", "altitudeAccuracy", "heading", "speed"];            
        for (var i = 0; i < properties.length; i++) {                
        var value = pos.coords[properties[i]];
                document.getElementById(properties[i]).innerHTML = value;
            }
            document.getElementById("timestamp").innerHTML = pos.timestamp;
        }        function handleError(err) {
            document.getElementById("errcode").innerHTML = err.code;
            document.getElementById("errmessage").innerHTML = err.message;
        }    </script></body></html>

4. Monitor position changes

Below we introduce the use of watchPosition method to monitor position changes. Its usage is the same as getCurrentPosition. . Let’s look at an example:

<!DOCTYPE HTML><html><head>
    <title>Example</title>
    <style>
        table{border-collapse: collapse;}
        th, td{padding: 4px;}
        th{text-align: right;}
    </style></head><body>
    <table border="1">
        <tr>
            <th>Longitude:</th>
            <td id="longitude">-</td>
            <th>Latitude:</th>
            <td id="latitude">-</td>
        </tr>
        <tr>
            <th>Altitude:</th>
            <td id="altitude">-</td>
            <th>Accuracy:</th>
            <td id="accuracy">-</td>
        </tr>
        <tr>
            <th>Altitude Accuracy:</th>
            <td id="altitudeAccuracy">-</td>
            <th>Heading:</th>
            <td id="heading">-</td>
        </tr>
        <tr>
            <th>Speed:</th>
            <td id="speed">-</td>
            <th>Time Stamp:</th>
            <td id="timestamp">-</td>
        </tr>
        <tr>
            <th>Error Code:</th>
            <td id="errcode">-</td>
            <th>Error Message:</th>
            <td id="errmessage">-</td>
        </tr>
    </table>
    <button id="pressme">Cancel Watch</button>
    <script>
        var options = {
            enableHighAccuracy: false,
            timeout: 2000,
            maximumAge: 30000
        };        var watchID = navigator.geolocation.watchPosition(displayPosition, handleError, options);
        
        document.getElementById("pressme").onclick = function (e) {
            navigator.geolocation.clearWatch(watchID);
        };        function displayPosition(pos) {            
        var properties = ["longitude", "latitude", "altitude", "accuracy", "altitudeAccuracy", "heading", "speed"];            
        for (var i = 0; i < properties.length; i++) {                
        var value = pos.coords[properties[i]];
                document.getElementById(properties[i]).innerHTML = value;
            }
            document.getElementById("timestamp").innerHTML = pos.timestamp;
        }        function handleError(err) {
            document.getElementById("errcode").innerHTML = err.code;
            document.getElementById("errmessage").innerHTML = err.message;
        }    </script></body></html>

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