apply_timezone() Takes date time text in
Arguments
- dt
One or more date time strings e.g. "2024-05-28 3:30:00" or a date object made from such a string without specifying the timezone. In the later case the listed times should be in the timezone indicated by
tz, but quite possibly the defined timezone of the date time object won't be correct.- tz
Either (1) "timezone" string expressing the offset from GMT e.g. "GMT-4:00"- this is the format used by HOBOware and saved into the metadata object and file, but is not a standard timezone; or (2) a standard time zone e.g. "EDT" as appears in other calibrated files.
Value
A date time object in with a defined timezone that together locates the observations correctly in time (but may not be in the local timezone).
Details
HOBOware is configured to log the time based on an offset from GMT. The BuzzardsBay package stores that "timezone", but the offset isn't a valid timezone. This gets around that by adding the offset hours and then defining the timezone as "UTC" - thus the points are correctly located in time - but not in the local timezone.
More recent ONSET software uses a valid time zone ("EDT") and for data
processed with this software that timezone is recorded in the metadata.
For these timezones apply_timezone() simply returns the date-times
in dt with tz specified.
For plotting convert the string to a date-time object without specifying the timezone and ignore the default (UTC) timezone and thus do NOT use this function.
However, for some uses it's important that the times are fully and correctly defined. For example to looking up the correct sunrise and sunset times, or tide charts. For these uses it's not actually important that its in the local timezone and so UTC with the offset applied is fine, as long as the resulting object correctly identifies when the data was collected.