Algorithms Index
PackData
Author : Bernard Schutz
Version: 1.1
Input Types : SampleSet
Output Types : SampleSet
Date : 25 June 2000
Contents
Description of PackData
PackData takes successive input SampleSets, concatenates them, and then
re-packs them for output into SampleSets of a different length, possibly
with overlaps (back-spacings like this can be important for searching for
signals using FFTs). The user chooses the new output set length and the
overlap, both given as numbers of elements. This unit can be used to prepare
sets for the Fourier transform by making their length a convenient power
of 2.
PackData correctly re-adjusts the acquisition time of data sets as it
outputs them, so that the timing information is correct.
Using PackData
Packdata has a parameter window in which the user can set the length of
the output set and the number of elements overlapping successive sets;
if this is set to a number n then the last n elements of one output will
be identical to the first n elements of the next. The default output length
is 1024 elements, and the default overlap is 0. The output can be any number;
in particular, it does not matter whether it is larger than or smaller
than the input data set length.

Sometimes one wants to fix the length or overlap of data sets by giving
the amount of time rather than the number of samples. This can be done
in Triana using parameter-passing and arithmetic. PackData's node editor
window allows one to choose to input values for the number of samples and/or
the overlap. These in turn can be calculated from parameter outputs from
previous units where the sampling rate of the SampleSet was fixed, or by
using the output of the unit SampleRate
in the DataParam toolbox. Here is an example of PackData's node-editor
window being used to create an input node for the number of samples: