Why doesn't timezone work with datetime

I want to convert a posix time to a datetime for the time zone at a specific longitude. The timezone function gives you the time zone at a specific longitude, but none of the outputs are accepted by datetime.

[a,b,c] = timezone(-80)

a = 5

b = 'R'

c = '+5 R'

try
    datetime(1685585049.879,'ConvertFrom','posixtime','TimeZone',a)
end
try
    datetime(1685585049.879,'ConvertFrom','posixtime','TimeZone',b)
end
try
    datetime(1685585049.879,'ConvertFrom','posixtime','TimeZone',c)
end

Answer 1

[Star Strider]

The timezone function is from the Mapping Toolbox, and its results are not compatible with the datetime function. The otherwise compatible timezones function does not take longitude arguments.

Try this instead —

TZ = string(fix(-80/15))                            % Time Zone (-80° Longitude)

TZ = "-5"

Time = datetime(1685585049.879,'ConvertFrom','posixtime','TimeZone',TZ)

Time = datetime
   31-May-2023 21:04:09

.

Answer 2

[Seth Furman]

Adding to @Star Strider's answer:

The value of TimeZone can be an ISO 8601 character vector of the form +HH:mm or -HH:mm; for example, '+01:00', to specify a time zone that is a fixed offset from UTC.

https://www.mathworks.com/help/matlab/ref/datetime.html#buhzxmk-1-TimeZone

lon = 80;
zd = timezone(lon)

zd = -5

tz = compose("%+03d:00",zd)

tz = "-05:00"

dt = datetime(1685585049.879,ConvertFrom="posixtime",TimeZone=tz)

dt = datetime
   31-May-2023 21:04:09