reducer.var.welford function outputs for each tick the variance of the values of Geo Time SeriesTM which are in the same equivalence class.
This is similar to
reducer.var except this version implements Welford's method which is 10% slower but is much less subject to numerical instability.
It operates on LONG and DOUBLE.
The location and elevation returned are the first encountered.
This reducer takes an additional boolean parameter to choose if Bessel correction should be applied.
It will exclude all null values when computing the result.