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: