Find the cal BP ages where the calibration curve crosses a given C14 age. This function is for illustration only and not to be used for, e.g., calibration, because intercept calibration is an outdated method.
C14tocalBP(
y,
cc = 1,
postbomb = FALSE,
rule = 2,
cc.dir = NULL,
thiscurve = NULL
)The cal BP age(s) belonging to the entered C14 age
The C14 age.
calibration curve for C14 (see caldist()).
Whether or not to use a postbomb curve (see caldist()).
How should R's approx function deal with extrapolation. If rule=1, the default, then NAs are returned for such points and if it is 2, the value at the closest data extreme is used.
Directory of the calibration curves. Defaults to where the package's files are stored (system.file), but can be set to, e.g., cc.dir="curves".
As an alternative to providing cc and/or postbomb, the data of a specific curve can be provided (3 columns: cal BP, C14 age, error).
Maarten Blaauw
. Whereas each cal BP age will only have one single IntCal radiocarbon age (mu), the same cannot be said for the other way round. Recurring C14 ages do happen, especially during periods of plateaux and wiggles. Therefore, there can be multiple cal BP ages for a single C14 age. In the early days, radiocarbon calibration used an 'intercept method' to find possible calendar ages belonging to a radiocarbon age, but this is problematic since small deviations in the C14 age can easily cause more or fewer crossing cal BP ages (try for example C14tocalBP(130) vs C14tocalBP(129)), and moreover, this approach does not deal well with the errors in either a date of the calibration curve. Therefore, the probabilistic approach to radiocarbon calibration (which starts with a cal BP age and then looks up the corresponding C14 age) has taken over as the standard.
y <- 130
calibrate(y,10)
abline(h=y)
abline(v=C14tocalBP(y))
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