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acq.channeldata [2010/06/21 07:40] (current)
jochen created
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 +====== ACQ::​ChannelData - access channel data in raw sampling frequency ======
 +===== Motivation =====
 +Different object types have different field names/​properties and/or store the underlying data differently (e.g. in a samples-by-channel table or in different fields). This method (which is available also for the [[xff - NTT format|NTT - numeric text table]] format/​object) allows to correctly overload with different object types (useful for shared code across types).
 +===== Method reference ('​acq.Help('​ChannelData'​)'​) =====
 +<​file>​ ACQ::​ChannelData ​ - get channel data from RawData/​Channel(C).Data
 + ​FORMAT: ​      cdata = acq.ChannelData(channel [, idx])
 + Input fields:
 +       ​channel ​    ​channel number
 +       ​idx ​        ​indices (passed on!)
 + ​Output fields:
 +       ​cdata ​      ​channel data</​file>​
 +===== Usage =====
 +There are two main uses:
 +  * getting all the data in one channel: <code matlab>% whole channel
 +ch1data = acq.ChannelData(1);</​code>​
 +  * getting only part of the data (e.g. first 10,000 samples): <code matlab>% only part of the data
 +ch1snip = acq.ChannelData(1,​ 1:​10000);</​code>​
 +===== Notes =====
 +Although the second syntax above might suggest otherwise, the returned argument is always a column vector (suitable for first-dimension transformations and statistics, e.g. mean, etc.).
 +The [[xff - ACQ format|ACQ]] format/​object stores the scaling information as part of the per-channel information. To obtain the correct values (scaled as input, e.g. in case the data on file is in 16-bit short integer precision), this function automatically multiplies the ''​.RawData''​ content (if necessary) with the scaling factor and adds the offset. The result of this operation is then also stored in ''​.Channel(C).Data'',​ so that it only needs to be performed once.
acq.channeldata.txt ยท Last modified: 2010/06/21 07:40 by jochen