I have an API that is returning data like this:
[[1484197227000,55.9],[1484334143000,58.0]]
The timestamps are already formatted in the user's local timezone by the server, so I thought by setting useUTC to false, that would work out - in this particular example, the user's timezone is EST. If I take the timestamp of the first data point and see what it evaluates to in the browser, I get:
new Date(1484197227000)
Thu Jan 12 2017 00:00:27 GMT-0500 (EST)
Which is what I would expect.
However, Highstock is translating this date to 05:00:27, so it's still 5 hours off. How can I get Highstock to just honor the timestamp without attempting to transform it at all? If I turn useUTC back on, then it is 8 hours off. Do I need to do something like write a custom getTimezoneOffset function to subtract out the timezone that the server already translated the date to? That seems a bit odd to me.
Related
how can we convert the GMT to local SQL DATE?
When i store GMT time , then 1 hour is subtracted from this value.
please help me.
Your question is a bit ambiguous as written, but I am guessing that you want to convert a UTC datetime (sometimes called GMT or Zulu time) into a datetime in your local timezone.
You indicate that your local time zone is -1 hour offset from UTC time.
In this case you simply use the DATEADD function:
SET MyTimeLocal = DATEADD(HH, -1, MyTimeGMT)
Note that this will only work so long as your time zone really is one hour before UTC time. If your location uses daylight saving time, this will be wrong as soon as the time changes, and it will be extra wrong when the time to be converted falls in the crack of the clock change.
There are many better ways to do this in general, but to give a general solution we would need to know what version of SQL is being used and what exactly you are trying to accomplish.
Background
I am investigating different use cases of moment.js for a project but am stumped on the issue of daylight savings ending in the fall. Before asking my question, since I want to be clear and provide background for others who have similar questions, let me explain what I am doing and what found with spring daylight savings.
First, I am working with UTC timestamps and America/New_York timestamps. In the US, daylight savings in 2017 begins on March 12 at 2AM (skipping from 2:00:00AM to 3:00:00AM) and ends on November 5 at 2AM (reverting from 2:00:00AM to 1:00:00AM). Since I also always know the target time zone (America/New_York) that I need to convert to, I will not rely upon moment.js to detect my local time zone and instead explicitly specify the time zone I want.
During the spring when daylight savings goes into effect, the time zones that observe daylight savings, like America/New_York, jump forward an hour. moment.js handles this just fine.
For example, if I pass moment.js a UTC timestamp for the time one second before daylight savings goes into effect for America/New_York, it looks like this:
moment('2017-03-12T06:59:59Z').tz('America/New_York').format('YYYY/MM/DD hh:mm:ss a z')
The input above is taken as UTC because of the Z on my timestamp and I am explicitly setting the target timezone with .tz('America/New_York') so that it doesn't use local system time.
Alternatively using moment-timezone I can explicitly set the input time zone as UTC and set the output as America/New_York.
moment.tz('2017-03-12T06:59:59', 'UTC').tz('America/New_York').format('YYYY/MM/DD hh:mm:ss a z')
Either way, the result is 2017/03/12 01:59:59 am EST.
Then, I run the same commands for a moment just one second later. I will just use the format given in the first example above where I specify the time as UTC and then convert it to America/New_York time:
moment('2017-03-12T07:00:00Z').tz('America/New_York').format('YYYY/MM/DD hh:mm:ss a z')
And my result is correct as expected: 2017/03/12 03:00:00 am EDT - due to daylight savings the time skipped ahead by one hour.
I can then use moment-timezone to go back the other way by passing in an America/New_York timestamp and converting it to UTC.
moment.tz('2017-03-12T01:59:59', 'America/New_York').utc().format('YYYY/MM/DD hh:mm:ss a z')
This gives me 2017/03/12 06:59:59 am UTC
And the next moment in the America/New_York time zone, because of daylight savings coming into play, is 03:00:00 so I convert that to UTC...
moment.tz('2017-03-12T03:00:00', 'America/New_York').utc().format('YYYY/MM/DD hh:mm:ss a z')
... and get 2017/03/12 07:00:00 am UTC which looks correct.
An hour was skipped ("lost") in America/New_York time, but moment can detect that and convert it to UTC.
In Summary, for the spring daylight savings change in the US, I can pass a UTC timestamp into either moment.js or moment-timezone and get back a timestamp in another time zone with the correct daylight savings offset also applied. I can also then pass an America/New_York timestamp into moment and get back a correctly converted UTC timestamp.
My Question
Great, so I want to do the same thing when daylight savings ends in the fall and of course it isn't that simple. My hypothesis is that due to daylight savings effectively causing an hour to "repeat", there is no way for moment to know the correct time UTC. In other words, where there was a gap of one hour when daylight savings started, now we have overlap of one hour.
Question (part 1): Is there a way to pass a relative timestamp and time zone into moment and get back the correct UTC time? When I tried this in the examples below, moment skips an hour on the UTC side.
moment.tz('2017-11-05T01:00:00', 'America/Denver').tz('UTC').format('YYYY/MM/DD hh:mm:ss a z') => "2017/11/05 07:00:00 am UTC"
moment.tz('2017-11-05T01:59:59', 'America/Denver').tz('UTC').format('YYYY/MM/DD hh:mm:ss a z') => "2017/11/05 07:59:59 am UTC"
moment.tz('2017-11-05T02:00:00', 'America/Denver').tz('UTC').format('YYYY/MM/DD hh:mm:ss a z') => "2017/11/05 09:00:00 am UTC"
moment.tz('2017-11-05T02:59:59', 'America/Denver').tz('UTC').format('YYYY/MM/DD hh:mm:ss a z') => "2017/11/05 09:59:59 am UTC"
I assume its because time is happening chronologically like in the example below. UTC offset context is not given therefore I assume that moment cant distinguish between the America/New_York timestamps preceded by asterisks:
*2017/11/05 01:00:00 am America/New_York => 2017/11/05 07:00:00 am UTC
*2017/11/05 01:59:59 am America/New_York => 2017/11/05 07:59:59 am UTC
*2017/11/05 01:00:00 am America/New_York => ???
*2017/11/05 01:59:59 am America/New_York => ???
2017/11/05 02:00:00 am America/New_York => 2017/11/05 09:00:00 am UTC
2017/11/05 02:59:59 am America/New_York => 2017/11/05 09:59:59 am UTC
Again, what I want to know is if there is a way around this? Currently the timestamps in the data that I have does not contain UTC offsets.
Question (part 2): If I am presenting data in the America/New_York time zone then is it correct to think that I will essentially have two hours of data points all stuffed into a (seemingly) single one hour period from 01:00:00 to 01:59:59 on November 5, 2017?
Related Topics
There are a few other topics on SO that are related to this but none that I have found pose or answer this same question. I will link a few here for reference:
Moment.js Convert Local time to UTC time does work
Initialize a Moment with the timezone offset that I created it with
It looks like you have thought the problem through and done some basic research. Thanks!
What you are describing is covered in the moment-timezone docs here. If the data isn't available as a UTC offset in your input, there's no way to tell the difference between the first or second occurrence of an ambiguous local time. Moment picks the first occurrence, because time moves in a forward direction, so this is usually the most sensible choice for most scenarios.
The problem is one of ambiguity. Even as just a human being, if I say "1:00 am on November 5th 2017 in New York" you don't know which of two points in time I'm describing.
That said, sometimes you have external knowledge that can help. For example, if you have an ordered set of timestamps containing time that skips backwards, then you know you encountered a fall-back transition. Say I'm recording data at 15 minute intervals in local time:
00:45
01:00
01:15
01:30
01:45
01:00 <--- this one comes next sequentially, but appears backwards, so infer transition
01:15
01:30
01:45
02:00
You'll have to write your own detection logic to compare one value to the next for that scenario. Also note that if you don't have any time that appears to be out of sequence, then you cannot be assured of which occurrence is being described. A "heartbeat" signal can assist with this in some scenarios.
Now how do you choose the second occurrence in Moment without knowing the offsets in advance? Like this:
First, grab the hasAmbiguousWallTime function from here.
Then define another function:
function adjustToLaterWhenAmbiguous(m) {
if (hasAmbiguousWallTime(m)) {
m.utcOffset(moment(m).add(1, 'hour').utcOffset(), true);
}
}
Now you can do this:
// start with the first occurrence
var m = moment.tz("2017-11-05T01:00:00", "America/New_York");
m.format(); // "2017-11-05T01:00:00-04:00"
// now shift it to the second occurrence
if (... your logic, such as wall time going backwards in sequence, etc. ...) {
adjustToLaterWhenAmbiguous(m);
m.format(); // "2017-11-05T01:00:00-05:00"
}
These two functions should probably be hardened and added to moment-timezone, but they should be sufficient for the scenario you describe.
A couple of other minor points:
Instead of moment.tz(s, 'UTC'), consider using moment.utc(s)
Instead of moment.tz(s, 'America/New_York').tz('UTC'), consider
using moment.tz(s, 'America/New_York').utc()
You may want to review the DST tag wiki for visualization of the problem space.
On part two of your question, yes - you'll end up stuffing two hours of data into what could possibly be visualized as a one-hour space. People have this problem with graphs and charts all the time. They graph something with a constant value over local time, then see a zeroing effect in the spring, and a doubling effect in the fall. Even if you tell moment to use the later occurrence, you won't avoid this unless you actually display the graph in UTC instead of local time.
I have been working on an application that takes dates from server in a certain format as given below.
"2015-02-03 00:00:00"
I want to show them with different UI format using NSDateFormatter
but as i change the timezone it show previous day or sometimes next day as i changing timezone. One important thing that server side date can be in any of timezone. So, we don't know what kind of timezone date has.
I need help to show this to the date as it is on server not change due to local timezone.
Thanks.
The simplest approach would be to parse it as if it were UTC - making it always valid, and without ever needing DST adjustments - and then format it in UTC as well. In other words, set the time zone of both the formatter and parser to UTC. For types which need a time zone, that's the simplest way of faking "There isn't a time zone here, just treat it all as local to an unspecified time zone."
I live in a country where they change the time twice a year. That is: there is a period in the year when the offset from UTC is -3 hours (-180 mins) and other period where the offset is -4 hours (-240 mins)
Grafically:
|------- (offset = -3) -------|------- (offset is -4) -------|
start of year mid end of year
My question is:
the "timezone" is just the number representing the offset? that is: my country has two timezones? or the timezone includes this information?
This is important because I save every date in UTC timezone (offset = 0) in my database.
Should I, instead, be saving the dates with local timezone and saving their offset (at the moment of saving) too?
Here is an example of a problem I see by saving the dates with timezone UTC:
Lets say I have a system where people send messages.
I want to have a statistics section where I plot "messages sent v/s hour" (ie: "Messages sent by hour in a regular day")
Lets say there are just two messages in the whole database:
Message 1, sent in march 1, at UTC time 5 pm (local time 2 pm)
Message 2, sent in august 1, at UTC time 5 pm (local time 1 pm)
Then, if I create the plot on august 2, converting those UTC dates to local would give me: "2 messages where sent at 1 pm", which is erratic information!
From the timezone tag wiki here on StackOverflow:
TimeZone != Offset
A time zone can not be represented solely by an offset from UTC. Many
time zones have more than one offset due to "daylight savings time" or
"summer time" rules. The dates that offsets change are also part of
the rules for the time zone, as are any historical offset changes.
Many software programs, libraries, and web services disregard this
important detail, and erroneously call the standard or current offset
the "zone". This can lead to confusion, and misuse of the data. Please
use the correct terminology whenever possible.
There are two commonly used database, the Microsoft Windows time zone db, and the IANA/Olson time zone db. See the wiki for more detail.
Your specific questions:
the "timezone" is just the number representing the offset? that is: my country has two timezones? or the timezone includes this information?
You have one "time zone". It includes two "offsets".
Should I, instead, be saving the dates with local timezone and saving their offset (at the moment of saving) too?
If you are recording the precise moment an event occurred or will occur, then you should store the offset of that particular time with it. In .Net and SQL Server, this is represented using a DateTimeOffset. There are similar datatypes in other platforms. It only contains the offset information - not the time zone that the offset originated from. Commonly, it is serialized in ISO8601 format, such as:
2013-05-09T13:29:00-04:00
If you might need to edit that time, then you cannot just store the offset. Somewhere in your system, you also need to have the time zone identifier. Otherwise, you have no way to determine what the new offset should be after the edit is made. If you desire, you can store this with the value itself. Some platforms have objects for exactly this purpose - such as ZonedDateTime in NodaTime. Example:
2013-05-09T13:29:00-04:00 America/New_York
Even when storing the zone id, you still need to record the offset. This is to resolve ambiguity during a "fall-back" transition from a daylight offset to a standard offset.
Alternatively, you could store the time at UTC with the time zone name:
2013-05-09T17:29:00Z America/New_York
This would work just as well, but you'd have to apply the time zone before displaying the value to anyone. TIMESTAMP WITH TIME ZONE in Oracle and PostgreSQL work this way.
You can read more about this in this post, while .Net focused - the idea is applicable to other platforms as well. The example problem you gave is what I call "maintaining the perspective of the observer" - which is discussed in the same article.
that is: my country has two timezones? or the timezone includes this information?
The term "timezone" usually includes that information. For example, in Java, "TimeZone represents a time zone offset, and also figures out daylight savings" (link), and on Unix-like systems, the tz database contains DST information.
However, for a single timestamp, I think it's more common to give just a UTC offset than a complete time-zone identifier.
[…] in my database.
Naturally, you should consult your database's documentation, or at least indicate what database you're using, and what tools (e.g., what drivers, what languages) you're using to access it.
Here's an example of a very popular format for describing timezones (though not what Windows uses).
You can see that it's more than a simple offset. More along the lines of offsets and the set of rules (changing over time) for when to use which offset.
Not sure if the title of my question was accurate so sorry if it's misleading, here goes.
I am doing some work with that involves timezones and i just want to make sure i get this right... if i want something to start at 03:00:00 my time and my timezone offset is -5 all i need to do is add 5 to 03:00:00 giving me 08:00:00 and that is the UTC time?
It depends what you mean by "timezone offset". Usually an offset is expressed as the amount added to UTC to get to local time, in which case you need to subtract it from the local time in order to get back to UTC (so it would be 22:00 on the previous day in your case).
So for example, Pacific Daylight Time has an offset of -7 - it's 7 hours behind UTC.
However, there are situations (annoyingly) where the offset is expressed the other way round, so make sure you know which way is appropriate for your specific context.
Note that knowing the offset doesn't mean you know the time zone - there can be multiple time zones with the same offset for a particular moment, but different rules for when the offset changes.
...Yes. Depending on what language you're doing it in, it may or may not be as easy as writing
time-offset;