What does Dates.hour(now(Dates.UTC)) return? Time in UTC?

joa-quim · March 30, 2023, 7:50pm

Can I use it to get an estimate of the Time Zone (less the day light saving shift)?
My intention is to get an approximate longitude of users location.

Sukera · March 30, 2023, 8:41pm

It gives you whatever is set as the system time, which doesn’t necessarily correspond to physical location. Some servers are exclusively configured with UTC+0 as their local time, regardless of physical location. It’s not really a good proxy variable for getting the longitude of a user.

JeffreySarnoff · March 30, 2023, 8:44pm

using Dates, TimeZones

function approx_longitude()
   # 15 degrees per hour
    (((now(localzone())).zone.offset.std.value) / (60*60)) * 15 
end

joa-quim · March 30, 2023, 9:29pm

Thank, I know about TimeZones but I don’t want to add a package dependency for this.

Sukera · March 30, 2023, 9:39pm

Short of querying that though, your only other semi-reliable option is to ask the user (or use an explicit location API of the OS) There’s a reason web browsers abstracted that away - most proxy variables for this aren’t reliable at all, not even checking the IP address.

jar1 · March 30, 2023, 9:42pm

Here’s what TimeZones.jl does

github.com

JuliaTime/TimeZones.jl/blob/c19864a60506e596b6f283845d902501e796571b/src/local.jl#L14


      
          
          
if Sys.iswindows()
              import TimeZones.WindowsTimeZoneIDs: WINDOWS_TRANSLATION
          end
          
          
"""
              localzone() -> TimeZone
          
          
Returns a `TimeZone` object that is equivalent to the system's current time zone.
          """
          function localzone()
              # Only allow creating a TimeZone using standard and legacy IANA time zone database
              # names. We allow the use of legacy names here as most operating systems still use the
              # legacy names.
              mask = Class(:STANDARD) | Class(:LEGACY)
          
          
    @static if Sys.isunix()
                  name = ""
          
          
        # Try getting the time zone from the "TZ" environment variable
                  # https://linux.die.net/man/3/tzset

joa-quim · March 30, 2023, 9:51pm

Guys, thanks for suggestions but I only wanted that the following map showing the the daylight terminators would center the map on user ~longitude. Not really important so that’s why I don’t want to add a dependency for it.

using GMT
solar(proj=:ortho, coast=true, terminators=:d, fill="navy@75", show=1)

rafael.guerra · April 1, 2023, 8:30am

FWIW, this SO solution prints the user IP lat-lon:

str = read(`curl ipinfo.io/loc`, String)

lon = last(split(chomp(str), ","))

joa-quim · April 1, 2023, 2:25pm

Thanks, and very fast.

rafael.guerra · April 1, 2023, 2:54pm

@joa-quim, would it be possible to show the full GMT example that centers the Earth map by longitude (and the daylight limits by local time) at the user’s location?

joa-quim · April 1, 2023, 6:06pm

I think that in current version
“solar()”
plots a map like I showed. For more examples see the solar man page and examples. To see the manual type
@? solar

(Sorry, I’m in travel)

joa-quim · April 1, 2023, 11:38pm

While I don’t integrate this into a more automatic way, you can do

split(readlines(`curl -s ipinfo.io/loc`)[1], ",")
2-element Vector{SubString{String}}:
 "38.7167"
 "-9.1333"

solar(proj=(name=:ortho, center=(-9.1, 38.7)), terminators=:d, fill="navy@75", coast=true, show=1)

And ofc you can use other projections and even add more terminators (twilights)

jar1 · April 1, 2023, 11:47pm

FWIW some people might not want a library making web requests unexpectedly.

joa-quim · April 1, 2023, 11:50pm

As is it is not unexpectedly. And when implemented it will be a documented option. So, a volunteer usage.