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Where are you? How to write a geosensitive application

Melksham's Spa HousesWhere are you? A question a web server will want to ask of a browser or app client, especially on mobile devices. And modern browsers, through Javascript, can send that vital information to the server. It's really useful in a wide variety of geographic data feeds - I've been working on a prototype listed building locator at http://melksh.am/lb which will find you the 15 nearest listed buildings to where you're located, tell you their direction, and let you move North South East or West to find more. This prototype already lists no fewer that 29,000 listed buildings within 25 miles of Melksham - so it covers Bradford-on-Avon, Chippenham, Malmesbury, Devizes, Trowbridge and Bath to name but a few ... links are provided for each building to the English Heritage site too.

So - how would you write this geolocation into you code?

I have a simple page [here] which uses Javascript to ask the user to permit his location to be used (that's built in to modern browsers) then submits it up as a form. You'll find lots of sophisticated examples on line... I have tried to keep mine simple to show you what's happening.

1. When you load the page, it runs the Javascript:

  <body onload='reportwhere()'>

2. The reportwere function runs the built in geolocation, passing the values it gets to two other functions which I've called nextpage and errhandler - the first if the user approves of his location being sent to the server, the second if he does not approve or geolocation isn't working:

  function reportwhere() {
    navigator.geolocation.getCurrentPosition(nextpage,errhandler);
  }


3. These two functions save the status code, and location if it's available, into variables which are passed in to another function which calls up the next page

  function nextpage(position) {
    var latitude = position.coords.latitude;
    var longitude = position.coords.longitude;
    post_to_url("http://www.wellho.net/twapp/railinfo.php",{'scode':0, 'lati':latitude, 'longi':longitude})
  }
  function errhandler(problem) {
    var whatswrong = problem.code;
    post_to_url("http://www.wellho.net/twapp/railinfo.php",{'scode':whatswrong})
  }


4. Here's that function that calls up the next page:

  function post_to_url(url, params) {
    var form = document.createElement('form');
    form.action = url;
    form.method = 'GET';
    for (var i in params) {
      if (params.hasOwnProperty(i)) {
        var input = document.createElement('input');
        input.type = 'hidden';
        input.name = i;
        input.value = params[i];
        form.appendChild(input);
      }
    }
    form.submit();
  }


Moving on, I've pointed that form at a short piece of PHP code (full source [here] which will report on which railway stations you're nearest to, indicating which are busiest and adding a link to live departure boards. Again this is a prototype...


Illustration - Melksham's Spa Houses, dating from 1815.
(written 2013-09-18, updated 2013-09-21)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
H309 - PHP - Maps, Graphics and Geographics
  [4655] Image indexer / thumbnail display scripts in PHP - (2016-02-25)
  [4437] Adding a PHP build option, rotating an image based on camera data, and a new look at thumbnails in PHP - (2015-02-22)
  [4365] The changing face of Christmas - (2014-12-26)
  [3817] Fpdf - generating .pdf documents easily from your PHP program - (2012-07-24)
  [3734] QR codes with marketing logos embedded - (2012-05-16)
  [3584] QR codes - graphics images that provide quick phone links - (2012-01-18)
  [3536] UK Mapping Data - and more to come - under government Open Data measures - (2011-12-03)
  [3447] Needle in a haystack - finding the web server overload - (2011-09-18)
  [3211] Computer Graphics in PHP - World (incoming data) to Pixel (screen) conversion - (2011-03-24)
  [3197] Finding and diverting image requests from rogue domains - (2011-03-08)
  [3133] An image from a website that occasionally comes out as hyroglyphics - (2011-01-14)
  [3027] Server logs - drawing a graph of gathered data - (2010-11-03)
  [2939] Protecting your images from use out of context - (2010-08-29)
  [2729] Uploading a document or image to its own URL via a browser - (2010-04-18)
  [2675] Redirecting to your main domain for correct security keys - (2010-03-13)
  [2583] Reducing image size on digital photos - PHP - (2010-01-17)
  [2390] Dynamic / changing images on your web page - (2009-09-01)
  [2361] Geocoding - converting address to latitude / Longitude with PHP via Google - (2009-08-14)
  [2343] World Flags in your PHP pages - (2009-08-10)
  [1956] Images for Christmas - (2008-12-21)
  [1923] Making it all worthwhile - (2008-12-04)
  [1756] Ever had One of THOSE mornings? - (2008-08-16)
  [1752] Dynamic maps / geographics in PHP - (2008-08-13)
  [1734] All around the world? - (2008-08-03)
  [1724] addslashes v mysql_real_escape_string in PHP - (2008-07-27)
  [1628] Gant charts - drawing them with a PHP script - (2008-05-03)
  [1391] Ordnance Survey Grid Reference to Latitude / Longitude - (2007-10-14)
  [1390] Converting from postal address to latitude / longitude - (2007-10-13)
  [1389] Controlling and labelling Google maps via PHP - (2007-10-13)
  [1194] Drawing hands on a clock face - PHP - (2007-05-19)
  [1104] Drawing dynamic graphs in PHP - (2007-03-09)
  [937] Display an image from a MySQL database in a web page via PHP - (2006-11-22)
  [665] PHP Image viewing application - (2006-04-01)
  [563] Merging pictures using PHP and GD - (2006-01-13)
  [320] Ordnance Survey - using a 'Get a map' - (2005-05-22)

W604 - Web and Intranet - Beyond the Server
  [2355] See this page in French - (2009-08-13)
  [468] Stand alone PHP programs - (2005-10-18)


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Horse's mouth home
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Changing transport and destinations - looking forward to a good future
Some other Articles
Welcome to Salford and Oldham
Grumbling about trains? Buses can be far worse!
Exceptionally, I sign a petition - on a life and death issue for Irish dogs
Changing transport and destinations - looking forward to a good future
Where are you? How to write a geosensitive application
Setting and publishing your hours to suit your customer base
International and off island travel from Melksham
An alternative format for a new train service timetable
What would the extra trains from Melksham mean to your journey?
Train and Rail Travel - who runs it and where do I ask questions?
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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