R: Adjust the time within Oce object

retime {oce} | R Documentation

## Adjust the time within Oce object

### Description

This function compensates for drifting instrument clocks, according to t'=t + a + b*(t-t0), where t' is the true time and t is the time stored in the object. A single check on time mismatch can be described by a simple time offset, with a non-zero value of `a`, a zero value of `b`, and an arbitrary value of `t0`. Checking the mismatch before and after an experiment yields sufficient information to specify a linear drift, via `a`, `b`, and `t0`. Note that `t0` is just a convenience parameter, which avoids the user having to know the "zero time" used in R and clarifies the values of the other two parameters. It makes sense for `t0` to have the same timezone as the time within `x`.

### Usage

    retime(x, a, b, t0, debug = getOption("oceDebug"))

### Arguments

`x` | an oce object.
`a` | intercept (in seconds) in linear model of time drift (see “Details”).
`b` | slope (unitless) in linear model of time drift (unitless) (see “Details”).
`t0` | reference time (in `POSIXct()` format) used in linear model of time drift (see “Details”).
`debug` | a flag that, if nonzero, turns on debugging.

### Details

The returned object is computed by linear interpolation, using `approx()` with `rule=2`, to avoid `NA` values at the start or end. The new time will be as given by the formula above. Note that if the drift is large enough, the sampling rate will be changed. It is a good idea to start with an object that has an extended time range, so that, after this is called, `subset()` can be used to trim to a desired time range.

### Value

A new object, with time and other data adjusted.

### Author(s)

Dan Kelley

### Examples

    library(oce)
    data(adv)
    adv2 <- retime(adv,0,1e-4,as.POSIXct("2008-07-01 00:00:00",tz="UTC"))
    plot(adv[["time"]], adv2[["time"]]-adv[["time"]], type='l')

[Package oce version 1.2-0 Index]