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Geolocation API overview

From: HTML5 First Look

Video: Geolocation API overview

One of the most confusing things about HTML5 is deciphering what is and what is not HTML5. There are multiple associated technologies and APIs that have at various times either been a part of the HTML5 specification or have been labeled as being HTML5 for lack of a better buzzword. In this chapter, we are going to discuss some of the technologies associated with HTML5 and I want to start with the Geolocation API. The Geolocation API allows you to build applications that can determine where the user is and then share or act on that information.

Geolocation API overview

One of the most confusing things about HTML5 is deciphering what is and what is not HTML5. There are multiple associated technologies and APIs that have at various times either been a part of the HTML5 specification or have been labeled as being HTML5 for lack of a better buzzword. In this chapter, we are going to discuss some of the technologies associated with HTML5 and I want to start with the Geolocation API. The Geolocation API allows you to build applications that can determine where the user is and then share or act on that information.

The specification is currently in the working draft stage. Although you can view the latest editor's draft on the W3's site. While in the past, many web applications have used IP addresses to determine location, the Geolocation API leaves the method of discovery up to the user agent and gives authors a set of methods and objects to handle and process location data. This approach is much more flexible. It has a higher degree of accuracy and allows authors to take advantage of the many new powerful location-aware mobile devices.

Unlike using IP addresses for location, the Geolocation API is opt-in, meaning the user has to give permission to the application in order for the location data to be received. This addresses privacy concerns around the use of Geolocation and needs to be accounted for in the planning and design of any location-aware application. Currently, the Geolocation API is supported by Chrome versions 5 and above, Firefox versions 3.5 and above, Safari 5.0 and above, and on recent iPhone and Android operating systems.

While support is increasing, you will have to use workarounds if you want your application to work in non- supported devices or browsers. We are going to talk more about those in just a moment. Now that we know what the Geolocation API is, let's take a closer look at how it works. The core of the Geolocation API is built around the global navigator object. Using the navigator object, you can use two methods. getCurrentPosition and watchPosition to retrieve location data. The getCurrentPosition method is a one-shot method that retrieves a single set of data.

The watchPosition method creates a watch that allows applications to track location data over a period of time. Here's a sample function call for location data. As you can see, this uses a pretty simple form of Geolocation detection. First, we check to see if the Geolocation object exists. If it does, then we call for the data. If it doesn't, we could use one of our workarounds like Google Gears or simply inform the user that this device doesn't support Geolocation. You could also use a more robust detection method, such as the Modernizr library that we discussed earlier.

The call itself returns two functions that we then must define. plotLocation is the name I have given to the handler that is called if the method is successful. The second handler, plotError, is called if the location is not received. Now this is an optional handler. It's not required for getCurrentPosition to work. It's worth mentioning here that the Geolocation API has extensive error handling and allows you to respond to errors at any stage of the application. Okay, so let's say your call was successful. Well, now what? Well the callback function is going to contain an object with two properties.

The coords property and timestamp. As you can guess, the timestamp tells you when the data was received, which allows your applications to react out current position data is. The coords object contains a lot more information. It handles latitude, longitude, altitude accuracy, altitudeAccuracy, heading and speed. If a device is unable to supply any of these properties, a null value is going to be returned for them. So now that we've got that down, let's take a look at a simple callback function.

Here we've received the position object and retrieved the latitude and longitude coordinates from the coord object. Those could then be passed to a Google Maps for example, as a request for a new or updated map. There are of course many additional methods and objects available through the Geolocation API. So be sure to dig into the specification for more information and some sample code. Before we wrap up, I want to mention a couple of important considerations for developing apps with Geolocation. First, be aware of the opt-in nature of the Geolocation API.

The user acceptance interface is device-dependent and will change based on where your app is accessed. Also, the opt-in notifications tend to be what we call "blocking," meaning the user must accept in order for the application to continue. Making sure that you inform your user very early in the application process that they must agree to share their location will make for a much more successful application. Finally, the current uneven implementation of the Geolocation API means that you're going to need to detect for its support and provide fallback content and perhaps an alternate way of providing location data.

I recommend using modernizer for detection, and Google Gears is an open-source browser plug-in that can provide location data for older browsers. You also want to familiarize yourself with the device-specific Geolocation APIs that are common to many mobile devices. A good way to take care of all these options at once is to use Geo.js, an open-source JavaScript library hosted by Google that helps to blend multiple Geolocation APIs. If you want to see Geolocation in action, check out some of the following demos.

I think you'll agree that while not strictly HTML5, the Geolocation API is going to allow you to create some very interesting next-generation web applications.

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This video is part of

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HTML5 First Look

50 video lessons · 74288 viewers

James Williamson
Author

 
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  1. 3m 56s
    1. Welcome
      1m 1s
    2. Using the exercise files
      1m 50s
    3. Who is this course for?
      1m 5s
  2. 21m 12s
    1. Exploring prior standards
      4m 26s
    2. Why do we need HTML5?
      3m 32s
    3. HTML5 timeline
      4m 24s
    4. Current HTML5 support
      4m 25s
    5. What HTML5 is (and what it isn't)
      4m 25s
  3. 27m 49s
    1. HTML5 vs. HTML4
      3m 25s
    2. New structural tags
      6m 1s
    3. New content tags
      4m 7s
    4. New application-focused tags
      5m 32s
    5. Deprecated elements
      4m 28s
    6. API overview
      4m 16s
  4. 22m 29s
    1. Content models
      5m 33s
    2. Understanding the outline algorithm
      3m 21s
    3. The role of ‹div› tags
      4m 20s
    4. Using ID and class attributes
      2m 6s
    5. DOCTYPE declarations
      4m 16s
    6. Character encoding
      2m 53s
  5. 41m 27s
    1. Basic page structure
      3m 40s
    2. Structuring top-level elements
      7m 30s
    3. Structuring interior content
      8m 42s
    4. Building headers
      9m 11s
    5. Checking document outlines
      5m 46s
    6. Ensuring cross-browser structure
      6m 38s
  6. 27m 53s
    1. New input types
      5m 57s
    2. Setting form autofocus
      2m 53s
    3. Using placeholder data
      4m 4s
    4. Marking required fields
      3m 24s
    5. Working with number inputs
      5m 49s
    6. Using date pickers
      5m 46s
  7. 1h 1m
    1. Canvas overview
      6m 21s
    2. Adding canvas content
      8m 58s
    3. Drawing in the canvas environment
      12m 9s
    4. Drag-and-drop API overview
      6m 18s
    5. Offline applications overview
      7m 11s
    6. Video overview
      5m 45s
    7. Encoding video
      8m 23s
    8. Adding video
      5m 58s
  8. 57m 33s
    1. Geolocation API overview
      5m 50s
    2. Web storage API overview
      5m 40s
    3. WebSockets overview
      4m 16s
    4. CSS3 overview
      6m 38s
    5. Enhancing typography with CSS3
      7m 42s
    6. Using @font-face
      7m 11s
    7. Styling HTML5 with CSS3
      10m 23s
    8. Using CSS3 transitions
      9m 53s
  9. 5m 6s
    1. Final thoughts
      3m 49s
    2. Goodbye
      1m 17s

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