# numberAsPOSIXct: Convert a Numeric Time to a POSIXct Time In oce: Analysis of Oceanographic Data

## Description

There are many varieties, according to the value of `type` as defined in ‘Details’.

## Usage

 ```1 2``` ```numberAsPOSIXct(t, type = c("unix", "matlab", "gps", "argo", "ncep1", "ncep2", "sas", "spss", "yearday"), tz = "UTC") ```

## Arguments

 `t` an integer corresponding to a time, in a way that depends on `type`. `type` the type of time (see “Details”). `tz` a string indicating the time zone, used only for unix and matlab times, since GPS times are always referenced to the UTC timezone.

## Details

• `"unix"` employs Unix times, measured in seconds since the start of the year 1970.

• `"matlab"` employs Matlab times, measured in days since what MathWorks [1] calls “January 0, 0000” (i.e. ```ISOdatetime(0, 1, 1, 0, 0, 0)``` in R notation).

• `"gps"` employs the GPS convention. For this, `t` is a two-column matrix, with the first column being the the GPS "week" (referenced to 1999-08-22) and the second being the GPS "second" (i.e. the second within the week). Since the GPS satellites do not handle leap seconds, the R-defined `.leap.seconds` is used for corrections.

• `"argo"` employs Argo times, measured in days since the start of the year 1900.

• `"ncep1"` employs NCEP times, measured in hours since the start of the year 1800.

• `"ncep2"` employs NCEP times, measured in days since the start of the year 1. (Note that, for reasons that are unknown at this time, a simple R expression of this definition is out by two days compared with the UDUNITS library, which is used by NCEP. Therefore, a two-day offset is applied. See [2, 3].)

• `"sas"` employs SAS times, indicated by `type="sas"`, have origin at the start of 1960.

• `"spss"` employs SPSS times, in seconds after 1582-10-14.

• `"yearday"` employs a convention in which `t` is a two-column matrix, with the first column being the year, and the second the yearday (starting at 1 for the first second of January 1, to match the convention used by Sea-Bird CTD software).

## Value

A `POSIXct` time vector.

Dan Kelley

## References

[1] Matlab times: http://www.mathworks.com/help/matlab/ref/datenum.html

[2] NCEP times: https://www.esrl.noaa.gov/psd/data/gridded/faq.html#3

[3] problem with NCEP times: https://github.com/dankelley/oce/issues/738

`numberAsHMS`
Other things related to time: `ctimeToSeconds`, `julianCenturyAnomaly`, `julianDay`, `numberAsHMS`, `secondsToCtime`, `unabbreviateYear`
 ```1 2 3 4``` ```numberAsPOSIXct(0) # unix time 0 numberAsPOSIXct(1, type="matlab") # matlab time 1 numberAsPOSIXct(cbind(566, 345615), type="gps") # Canada Day, zero hour UTC numberAsPOSIXct(cbind(2013, 0), type="yearday") # start of 2013 ```