Weather Doodles
The masthead on NAIS changes based on the local weather, temperature, and sunset and sunrise time. I added the daylight check at Julie’s request. She didn’t understand why my weather doodle showed sunny at 5pm. This time of year, the sun sets at 4:29pm, and rises at 7:58am. I wish I was making this up.
First, I read in the XML file from the very helpful National Oceanic and Atmospheric Administration’s National Weather Service. They provide a number of great RSS feeds, of which I chose the hourly observations. I picked KRNT.xml, the feed for the Renton Municipal weather station, because it felt closest (knowing my geographic sense, I could be way off). Here’s the PHP code (remember, I can’t use file_get_contents() on a URL because of the PHP.ini security setting. I replaced it with the CURL call):
<?php
if (!file_exists($file) || !filemtime($file)>time()-30*60) {
$ch = curl_init('http://www.nws.noaa.gov/data/current_obs/KRNT.xml');
$fp = fopen('weather.xml', 'w');
curl_setopt($ch,CURLOPT_FILE,$fp);
curl_setopt($ch,CURLOPT_HEADER,false);
curl_setopt($ch,CURLOPT_FOLLOWLOCATION,true);
curl_setopt ($ch,CURLOPT_CONNECTTIMEOUT,3);
$result=curl_exec($ch);
curl_close($ch);
fclose($fp);
if ($result) {
$xml_parser=xml_parser_create();
$data=file_get_contents('weather.xml');
xml_parse_into_struct($xml_parser,$data,$values,$index);
$weather=$values[$index['WEATHER'][0]]['value'];
$temp=$values[$index['TEMP_F'][0]]['value'];
file_put_contents('weather',$weather.','.$temp);
unlink('weather.xml');
}
}
$weathertitle='Seattle WA: '.$weather.', '.$temp.'° F';
$s.='<a href="/" title="'.$weathertitle.'">';
The code checks the weather once every thirty minutes, and saves the parsed result to a flat file. I use this file as a cache so I don’t have to reparse the XML file each time. There is higher-level page cache (which I plan to write more about) that also uses flat files to take the load off the MySQL server, which seems to be the bottleneck in serving pages.
I plan to generalize the above code a bit in the future so when I travel, I can replace Seattle with my destination (and its corresponding weather station). While this would be a trivial change, it’s not very high on my list.
After I load the XML file, I use the PHP xml parser to parse the document and find the weather description and temperature. I called xml_parse_into_struct() to perform the parsing. I still don’t quite understand how the structure is created. Through trial and error, I found the appropriate structure and array elements.
For the daylight check, I used the convenient PHP functions date_sunrise() and date_sunset(). These functions use the longitude and latitude and return sunset and sunrise times for the requested day.
<?php
if (time()<date_sunrise(time(),SUNFUNCS_RET_TIMESTAMP,45,-122) || time()>date_sunset(time(),SUNFUNCS_RET_TIMESTAMP,45,-122))
$doodle='night-'.$doodle;
And then I have the weather parsing code. As I add more weather doodles, I continue to tweak the code. It turns out the weather service uses many phrases to describe weather conditions. Some examples: “Thunderstorm in Vicinity Hail Haze,” “Showers in Vicinity Fog/Mist,” and “Heavy Sand Storm.” At first, I created a huge switch/case statement to capture all of the phrases. After a bit of thought, I decided to fall back on simpler phrase searches through an if/else statement. I set it up as a hierarchy to ensure the most desirable doodle is selected, e.g., if it’s “Light Drizzle Fog/Mist” it chooses the fog doodle—mostly because it’s less common. Similarly, if there’s a mention of snow or frozen rain, it chooses the snow doodle.
I will add a more robust temperature/season check once I have more relevant doodles. I’m hemming and hawing because I’m not satisfied with the following code. But I’ll include it for completeness.
<?php
// Here for terminology: http://www.nws.noaa.gov/data/current_obs/weather.php
if (stristr($weather,'thunderstorm'))
$doodle='rain.png';
else if (stristr($weather,'ice') || stristr($weather,'snow') || stristr($weather,'hail'))
$doodle='snow.png';
else if (stristr($weather,'fog') || stristr($weather,'smoke'))
$doodle='fog.png';
else if (stristr($weather,'rain') || stristr($weather,'drizzle') || stristr($weather,'showers'))
$doodle='rain.png';
else if (stristr($weather,'cloud') || stristr($weather,'overcast'))
if (stristr($weather,'partly') || stristr($weather,'few'))
$doodle='sun-cloud.png';
else
$doodle='cloudy.png';
else if (stristr($weather,'breez') || stristr($weather,'wind'))
$doodle='rain.png';
else {
if ($temp>50)
$doodle='sun.png';
else
$doodle='sun-cold.png';
}
My next step is to get doodling. It’s great to have all this code, but it’s wasted if my weather doodle is always the same. I plan to have a bunch of rain and cloudy doodles for the winter, and many sunny doodles for the summer. In Seattle, the word rain is much like the word snow is to Eskimos: you need many words (and doodles) to capture its essence.