Using Google’s Weather API

I thought it would be a nice little project to write a tutorial on how to build a basic but powerful weather application for either mobile devices or the desktop. The application takes a set of Google weather API feeds and makes some simple decisions based on the output. For example we can recommend the user takes an umbrella if rain or storms are forecast, or whether the temperature warrants the need for warm clothes. Basic but nonetheless useful information.

The Logic Code

Lets have a quick run through at what the project consists of. Firstly we use the simplexml_load_file() PHP function to get the xml data for the given location. We then check to see if the current weather condition is in the XML file. If it doesn’t exist then we can make the assumption that the API feed couldn’t determine the location, bear in mind this is very basic error checking and if the feed fails it will still return this error.

We now do some basic data checking to to see what extra data we can give the user. Firstly we check on line 14 to see if the current weather and forecast are different, if they are different we’ll display the forecast if not we show just the current weather.

Next on lines 21 and 28 we do a simple check to see if the temperature is higher or lower than 20 degrees and echo whether it’s likely to be hot or cold.

Finally on lines 35 we check to see if the current or future forecast contains any rain or storms so we can recommend the user takes an umbrella. This is done using some basic PHP regular expression.

	// load the XML feeds for the Google Weather API
	$xml = simplexml_load_file('http://www.google.com/ig/api?weather='.urlencode($_GET['location']));
	$current = $xml->xpath("/xml_api_reply/weather/current_conditions");
	$forecast = $xml->xpath("/xml_api_reply/weather/forecast_conditions");

	// do a basic error check to see if we can get the current weather condition for the given location
	// if no return an error.
	if(!$current[0]->condition['data']){

		$error = 'Couldn\'t determine this location';

		}

	// is the current weather the same as the forecast? if not display the forecast
	if(strtolower($current[0]->condition['data'])!=strtolower($forecast[0]->condition['data'])){

	$outlook = 'but the forecast says '.strtolower($forecast[0]->condition['data']);	

		}

	// if the temp in degrees c is below 20 i.e. cold
	if($current[0]->temp_c['data']<=20){

	$coat = 'If you\'re going outside i\'d wrap up warm.';	

		}	

	// if the temp in degrees c is over 21 i.e. Warm / Hot
	if($current[0]->temp_c['data']>=21){

	$coat = 'You should be ok without warm clothes today.';	

		}		

	// check to see if there is rain or storms forecast
	if (preg_match("/\brain\b/i", $current[0]->condition['data']) ||
		preg_match("/\brain\b/i", $forecast[0]->condition['data']) ||
		preg_match("/\bstorm\b/i", $current[0]->condition['data']) ||
		preg_match("/\bstorm\b/i", $forecast[0]->condition['data'])
		){

		$umbrella = ' But <u>don\'t forget to take an umbrella</u>!';
		}

Displaying the data

<form action="" method="get">
<label for="location">Location</label>
<input type="text" class="location" name="location" value="<?php echo $_GET['location'];?>"/>
</form> 

<?php if(!empty($_GET['location'])){

	if($error){ echo '<div class="errors">'.$error.'</div>'; }else{

?>

<div class="weather_app">

<h1>Weather Summary for <?php echo $_GET['location'];?></h1>

<ul>
<li><?php echo '<img src="http://google.com'.$current[0]->icon['data'].'"/>'; ?> The weather in <?php echo $_GET['location'];?> is <strong><?php echo strtolower($current[0]->condition['data']).' '. $outlook;?></strong>. The temperature is currently <strong><?php echo $current[0]->temp_c['data']; ?>&deg;c (<?php echo $current[0]->temp_f['data']; ?>&deg;f)</strong>. <?php echo $coat;?> <?php echo $umbrella;?></li>
</ul>

</div>

<?php } } ?>