Comments on: Inside the AS3 Date class: Timezones and Daylight Saving Time http://www.computus.org/journal/?p=44 Exploring Digital Horology Fri, 03 Sep 2010 05:32:17 +0000 hourly 1 http://wordpress.org/?v=3.0.1 By: World Cup instant Twitter replay | Top Mobile Accessories http://www.computus.org/journal/?p=44&cpage=1#comment-7778 World Cup instant Twitter replay | Top Mobile Accessories Fri, 18 Jun 2010 01:40:24 +0000 http://www.computus.org/journal/?p=44#comment-7778 [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash’s Date object to ensure that everything would work in every possible timezone. On the other, we’d decided [...] [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash’s Date object to ensure that everything would work in every possible timezone. On the other, we’d decided [...]

]]> By: World Cup instant Twitter replay | World News http://www.computus.org/journal/?p=44&cpage=1#comment-7775 World Cup instant Twitter replay | World News Thu, 17 Jun 2010 15:43:32 +0000 http://www.computus.org/journal/?p=44#comment-7775 [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash’s Date object to ensure that everything would work in every possible timezone. On the other, we’d decided [...] [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash’s Date object to ensure that everything would work in every possible timezone. On the other, we’d decided [...]

]]> By: World Cup instant Twitter replay: how we did it | World News http://www.computus.org/journal/?p=44&cpage=1#comment-7774 World Cup instant Twitter replay: how we did it | World News Thu, 17 Jun 2010 15:13:33 +0000 http://www.computus.org/journal/?p=44#comment-7774 [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash’s Date object to ensure that everything would work in every possible timezone. On the other, we’d decided [...] [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash’s Date object to ensure that everything would work in every possible timezone. On the other, we’d decided [...]

]]> By: World Cup instant Twitter replay: how we did it #the guardian #world cup 2010 | soccer ts http://www.computus.org/journal/?p=44&cpage=1#comment-7773 World Cup instant Twitter replay: how we did it #the guardian #world cup 2010 | soccer ts Thu, 17 Jun 2010 14:45:43 +0000 http://www.computus.org/journal/?p=44#comment-7773 [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash's Date object to ensure that everything would work in every possible timezone. On the other, we'd decided to [...] [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash's Date object to ensure that everything would work in every possible timezone. On the other, we'd decided to [...]

]]> By: World Cup instant Twitter replay: how we did it | BB SPORT http://www.computus.org/journal/?p=44&cpage=1#comment-7772 World Cup instant Twitter replay: how we did it | BB SPORT Thu, 17 Jun 2010 13:34:37 +0000 http://www.computus.org/journal/?p=44#comment-7772 [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash’s Date object to ensure that everything would work in every possible timezone. On the other, we’d decided [...] [...] final challenges emerged just as we were preparing to go live. On one hand, I delved into the depths of Flash’s Date object to ensure that everything would work in every possible timezone. On the other, we’d decided [...]

]]> By: Ward Ruth http://www.computus.org/journal/?p=44&cpage=1#comment-7648 Ward Ruth Tue, 16 Mar 2010 16:33:25 +0000 http://www.computus.org/journal/?p=44#comment-7648 Thanks, very useful! Did note that for the getTimezone() method, I needed to use a more recent reference date (I develop on a Mac, so that may make a difference). I used 2000 instead of 0 (1900). Using the 0 date there was no difference in the timezoneOffset values for d1 and d2. Thanks, very useful! Did note that for the getTimezone() method, I needed to use a more recent reference date (I develop on a Mac, so that may make a difference). I used 2000 instead of 0 (1900). Using the 0 date there was no difference in the timezoneOffset values for d1 and d2.

]]> By: John http://www.computus.org/journal/?p=44&cpage=1#comment-6897 John Fri, 19 Jun 2009 13:18:27 +0000 http://www.computus.org/journal/?p=44#comment-6897 Just wanted to say a quick thanks to all the folks who have IM'd, Twittered and emailed me. I feel the love! I've got a great new gig in Covent Garden and I'm really excited about it. Normal service will be resumed asap... Just wanted to say a quick thanks to all the folks who have IM’d, Twittered and emailed me. I feel the love! I’ve got a great new gig in Covent Garden and I’m really excited about it. Normal service will be resumed asap…

]]> By: Immo http://www.computus.org/journal/?p=44&cpage=1#comment-6889 Immo Mon, 15 Jun 2009 15:08:23 +0000 http://www.computus.org/journal/?p=44#comment-6889 Hi John, only noticed your reply now.- The project is done and dusted and working just fine. I ended up writing a class that picks up the DST from a data list that can be updated whenever a territory decides to change their rules. I think I've got about 100 different entries there. Was quite a pain initially. I wrote a little script that detects the date for a specific day in the week, so to get e.g. the last Sunday in a month to switch DST. Works just fine but was very nervous when it came to the 'live' switch for the first time in spring ; ) Once again, thanks a lot for all the info on this page which helped very much. Hi John, only noticed your reply now.- The project is done and dusted and working just fine. I ended up writing a class that picks up the DST from a data list that can be updated whenever a territory decides to change their rules. I think I’ve got about 100 different entries there. Was quite a pain initially. I wrote a little script that detects the date for a specific day in the week, so to get e.g. the last Sunday in a month to switch DST. Works just fine but was very nervous when it came to the ‘live’ switch for the first time in spring ; ) Once again, thanks a lot for all the info on this page which helped very much.

]]> By: John http://www.computus.org/journal/?p=44&cpage=1#comment-5000 John Thu, 29 Jan 2009 22:11:45 +0000 http://www.computus.org/journal/?p=44#comment-5000 Hi there Immo - I share your pain. Your spot on so far. It's simple enough to determine "standard time" in any territory using a mixture of UTC (from the Date class) and some sort of TZD lookup table. It's also easy enough to get DST for the users current location using the functions in the article. The showstopper, as you've correctly spotted, is determining if DST is in effect in another territory. Unlike TZDs, DST is not a global standard. The dates for adoption vary from territory to territory, and even within territories. Check out the DST rules for the Navajo and Hopi indian reservations in Arizona for some idea of how convoluted this can get! The upshot of all this is that implementing a DST lookup in pure Actionscript would be a huge undertaking. Your best bet would be to use a lookup of the excellent TZ Database at http://www.twinsun.com/tz/tz-link.htm . You could either build yourself a web service (PHP uses the TZ DB) or you could build your app using AIR and use the internal SQLLite database. Hope that helps :) jd Hi there Immo – I share your pain. Your spot on so far. It’s simple enough to determine “standard time” in any territory using a mixture of UTC (from the Date class) and some sort of TZD lookup table.

It’s also easy enough to get DST for the users current location using the functions in the article. The showstopper, as you’ve correctly spotted, is determining if DST is in effect in another territory.

Unlike TZDs, DST is not a global standard. The dates for adoption vary from territory to territory, and even within territories. Check out the DST rules for the Navajo and Hopi indian reservations in Arizona for some idea of how convoluted this can get!

The upshot of all this is that implementing a DST lookup in pure Actionscript would be a huge undertaking. Your best bet would be to use a lookup of the excellent TZ Database at http://www.twinsun.com/tz/tz-link.htm . You could either build yourself a web service (PHP uses the TZ DB) or you could build your app using AIR and use the internal SQLLite database.

Hope that helps :)
jd

]]> By: Immo http://www.computus.org/journal/?p=44&cpage=1#comment-4998 Immo Thu, 29 Jan 2009 21:30:41 +0000 http://www.computus.org/journal/?p=44#comment-4998 Very interesting.- I am just building a world clock as a projector app in as3 where the user can set various clocks to their preferred cities. At the moment I am struggling to get my head around the DST. Let's say a user in Japan sets one of the clocks to 'London UK'. Sounds pretty easy in theory: UTC + TZD + DST would mean e.g. 'London UK' time in January : UTC + 0 + 0. But according to wwp.britishsummertime.co.uk the dates change to what the last Sunday of March or October is. Then again you get slightly different rules for the USA and every other territory.- Do you think there is some kind of clever proof way to find out whether a certain city in the world is actually in summertime or not (or whether it is using it at all) or do you think I will need to hardcode all the eventualities and check with if statements e.g. for 'London UK' if (UTC + TZD > 29 March) then DST = false? And next year update my code to Sunday the 28th of March? Is there a way to find out what the date for the last Sunday of a month would be in a certain year? I am kind of hoping there might be a clear logic solution to this. Any thoughts welcome. And thanks for the tips on this page. Already very helpful. Very interesting.- I am just building a world clock as a projector app in as3 where the user can set various clocks to their preferred cities. At the moment I am struggling to get my head around the DST. Let’s say a user in Japan sets one of the clocks to ‘London UK’. Sounds pretty easy in theory: UTC + TZD + DST would mean e.g. ‘London UK’ time in January : UTC + 0 + 0. But according to wwp.britishsummertime.co.uk the dates change to what the last Sunday of March or October is. Then again you get slightly different rules for the USA and every other territory.- Do you think there is some kind of clever proof way to find out whether a certain city in the world is actually in summertime or not (or whether it is using it at all) or do you think I will need to hardcode all the eventualities and check with if statements e.g. for ‘London UK’ if (UTC + TZD > 29 March) then DST = false? And next year update my code to Sunday the 28th of March? Is there a way to find out what the date for the last Sunday of a month would be in a certain year? I am kind of hoping there might be a clear logic solution to this. Any thoughts welcome. And thanks for the tips on this page. Already very helpful.

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