Returns the dateTime in relative time from the start time of the time axis, in the unit used by the file. The time axis must be a calendar type axis.

Note that for the equidistant axes, the first time step may be offset (see StartTimeOffset), however the time returned here is relative to the start time and not the first time step. This is matching the time returned by the read methods (Time).

Converts a time value in seconds to a time value in the unit of the temporal axis.