Coincidentally, TODAY I had to adjust my clock one hour forward because of DST 
(poor sleep =[). No so easy-to-solve problem, after all...

-----Mensagem original-----
De: Matijn Woudt [] 
Enviada em: domingo, 21 de outubro de 2012 10:30
Para: Maciek Sokolewicz
Cc: Karl DeSaulniers; php-general
Assunto: Re: [PHP] Re: User Timezone

On Sun, Oct 21, 2012 at 12:01 PM, Maciek Sokolewicz 
<> wrote:
> On 21-10-2012 01:11, Karl DeSaulniers wrote:
>>>> Thanks for the response. Yes, for the US I plan on calculating by 
>>>> state, but this website is not geared to just the US.
>>>> So I am looking for a solution that lets me also calculate by 
>>>> country/region.
>>>> Was looking on google and found geoip, but not sure if this will do 
>>>> the job I am looking for.
>>>> Anyone with experience on geoip that can send pointers?
>>>> Thanks,
>>>> Best,
>>>> Karl DeSaulniers
>>>> Design Drumm
>>> Geo IP is based on IP, and I must warn you that IP data is not 
>>> always accurate. Especially here in Europe, companies that are based 
>>> in multiple countries sometimes only register their IPs in a single 
>>> country, and share them between all the countries they are active in.
>>> This will give you wrong data from GeoIP. The time difference will 
>>> only be 1 hour at max, but still.
>> That was what my own suspicions were leading to.
>> I am familiar with the fact that ips can be spoofed.
>> Thanks for the corroboration.
>> Best,
>> Karl DeSaulniers
>> Design Drumm
> As Bart said, IP is not ideal for this situation.
> Since you do have information about the location of that person (as in 
> country and possible state), you can find out the timezone via a 
> static database.
> The HTML5 geolocation tool is nice, and would certainly help a lot! 
> However, be aware of the fact that it only works if there is the 
> device on which the browser runs actually has the ability to find out 
> its location. Many smartphones have GPS chips, but most PCs don't. 
> Asking a PC "where are you located?" the PC will answer "How should I know?".
> Luckily for you, the way of country and state is pretty easy. I've 
> handed you a list to find it in the USA. For most countries in the 
> world, there's a simple 1:1 mapping of timezone and country 
> (, there 
> are however 21 countries which have multiple timezones. In these 
> cases, you'll need extra information to be able to distinguish between them.
> For the USA, you already have a way.
> For (ex-)colonical islands and such (such as for France), you could 
> always add them to the country list:
> - France
> - France (Marquesas Islands)
> - France (Gambier)
> etc.
> Thus treating them as separate countries for your timezone db.
> In Russia, Canada, Australia, New Zealand, Brasil, Indonesia, 
> Kiribati, Mexico,Congo, Ecuador, Micronesia, Kazakhstan and Mongolia 
> you'll need to know their province / state to more accurately assess the 
> ideal timezone.
> So for most countries, it's a simple 1:1 translation. For the above 
> countries, you'll need some extra info, and translate further based on that.
> You should be able to find the info required yourself, it just takes a 
> while to collect it.
> Alternatively, and this is the most simple way; since you're asking 
> people for their country and such, simply also ask them about their 
> timezone. Don't bother automating and putting a heck of a lot of time 
> into hard to realize solutions, when you can ask a very simple and 
> easy-to-answer question to the browser instead. :)
> - Tul

Don't forget that some countries have DST, and some don't. And those that have 
DST, all use different dates.. So in to keep a static database you would also 
need to have DST info from all countries.

- Matijn

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