This mapper function takes the log of the single value in a sliding window in the base used as parameter to
If the sliding window is empty, the function does not return any value. If the sliding window contains more than a single value, an error is produced.
The associated location and elevation are those of the single value.
mapper.log function can be applied to data of type LONG or DOUBLE.
mapper.log function must be parameterized with the constant.
The result is always of type DOUBLE.
mapper.log mapper needs a single value sliding window, i.e. pre-window and post-window to 0.