Get current offset (incl. daylight savings) from UTC given the curren timezone

Question

I am getting data from some sensors that record values in their respective (local) timezone. The timestamps do not indicate what timezone the sensor is in. I'm calling googleway::google_timezone() to use the Google timezone API and get the timezone corresponding to the geoggraphical location of the sensors.

The output is as below (example):

google_timezone(latlon, key = mykey)
$dstOffset
[1] 0

$rawOffset
[1] -18000

$status
[1] "OK"

$timeZoneId
[1] "America/Toronto"

$timeZoneName
[1] "Eastern Standard Time"

The dstOffset field is 0 which seems to be incorrect (location is in Eastern Canada with daylight savings). I need to save the data in UTC on a server. Using attr to convert from the local timezone to UTC fails to address the daylight savings issue - the time difference remains constant regardless of the time of the year. For N. America, the time difference should change by 1 hour during the year on account of daylight savings. I've read the answers for Daylight saving time and time zone best practices and https://stackoverflow.com/tags/timezone/info which seem to suggest that this information (daylight savings) is somehow contained in the "timezone".

Is there any other way to do this?

Gautam Gautam · Accepted Answer · 2018-01-11T15:08:14

Finally figured it out - it's just the way the API reports values. I expected the output to report a standard raw offset of four hours with a one hour offset in winter (when daylight savings are in effect) and zero hour offset in summer. Google API does it the other way around:

Here's the raw output from Google Maps Timezone API (bypassing googleway::google_timezone()) for Jan 11, 2018 (daylight savings in effect):

dstOffset:  0
rawOffset:  -18000
status: "OK"
timeZoneId: "America/Toronto"
timeZoneName:   "Eastern Daylight Time"

And here's the output for April 21, 2018 (daylight savings NOT in effect):

dstOffset:  3600
rawOffset:  -18000
status: "OK"
timeZoneId: "America/Toronto"
timeZoneName:   "Eastern Daylight Time"

This is a bit counter-intuitive and confusing since the daylight saving offset has a non-zero value when the daylight savings are not in effect!!

Anyway, I hope this can help others and also that some day we'll be rid of the scourge that is daylight savings.

Get current offset (incl. daylight savings) from UTC given the curren timezone

1 Answers