This bucketizer function returns the variance of each bucket. The location and elevation returned are those associated with the most recent value in the bucket.
This is similar to
bucketizer.var except this version implements Welford's method which is 10% slower but is much less subject to numerical instability.
bucketizer.var.welford function can only be applied to values of type LONG or DOUBLE, when applied to STRING or BOOLEAN it does not return any value.