How can I read a binary file stream with many data type, as with AcqKnowledge physio binary data file?

[Donat-Pierre]

Thanks Charly. On Sunday, I implemented most of the lengthy file format spec for my AcqKnowledge file reader my application - minus the markers section . I even worked out how to re-organized interleaved data when one channel is sampled twice faster than the other one using a decimate and interleave subVI. Along the way, I spotted a couple of typos and located the section where 48bytes was added in the new version 3.8.1 (ver. # 41 in the header file), which not documented on BioPac webpage. There might be more new "item" saved just before the data section.
I am now cleaning up the code while I am waiting to get an update for the new file format for Version 3.8.1 from BioPac support. Note that version 3.8.1 is t
he latest version of AcqKnowledge released last September.
Among the thing I am cleaning, is the Read from file subvi which opens and closes file each time, so I use the file open and read and close instead. Also, I made an extensive use of case structure for every single variable or array. This would not be necessary if I only wanted to get channel data out. I also want to understand every parameters saved, or at least to get default values so that, in turn, I can generate *.acq file which can be read cleanly by AcqKnowledge software. I can post or email you the program when it is cleaned if you want.

Thanks again,
Donat-Pierre

[chilly_charly]

Bravo DP !
Happy to see that you are on the right path.
About the use of the sub-vis of the "read from file" vi, I'm not sure that this will save much time, but anyway it's the propedr way of doing it.
What you should also know is that the "Type cast" function works also on clusters. Means that you can decode a complex data structure with a simple node. Of course, there is still the indian question...
Keep wiring !

[Donat-Pierre]

When I started I was think of storing everything into an cluster. At the time a bundle by name each variable sounded ideal but I could not make ie work in a simple way or at all. But I think you are talking about something else here. I'll keep wiring and try few ideas out.

[TylerS]

As I understand it, you are looking for an example for reading binary data? There are a couple of shipping examples included with LabVIEW, specifically Read Binary File.vi and Display Acq'd File (Binary).vi that should demonstrate how this is done.

For the question of different data types, here is a KnowledgeBase that should help you understand which data type you should use. Also, LabVIEW data is written as Big Endian.

http://digital.ni.com/public.nsf/websearch/C261612DFCA8BD3586256CC300713EA6?OpenDocument

[drs T Schrama]

Dear fellow BIOPAC users,


I've been folling a labview course (Labview Basics I and II) and I would like to try to read BIOPAC .acq files. My goal is to read the real channel data and if possible the channel names. I am aware of the BIOPAC app note, but I was wondering...

Do you have a woring .vi to import .acq data? How far are you? Are you willing to share?


Best regards,

T Schrama


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drs. Thijs Schrama

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[TylerS]

T Schrama,

See if this discussion forum helps you at all:

http://forums.ni.com/ni/board/message?board.id=170&message.id=21926&requireLogin=False

Tyler S.

[drs T Schrama]

Thanks for the link. Again I see people mentioning the little- versus big- endian ...:


Quote :
"It might also be necesary for you to reverse the byte order of numeric data since LabVIEW is "big endian" while most PC applications are "little endian" "

Does this mean I need to reverse the data for all number formats (U8 I8 U16 I16 Double etc..) or do I need to reverse the data only for the "Double" number format?


I am getting there... slowly.... but it's a tedius work.. espessially when manufacturors documentations has errors...

thanks again,

cheers,
Thijs

[TylerS]

The endian format applies to all numeric data types.

Tyler S.

[drs T Schrama]

all formats! ok! Thanks, that did help a bit ;-).. I allready build 12 subVI's to read Biopac .ACQ file information, like number of channels, sample interval, headerlengths etc etc... it should be relatively easy to extract the data now... I could post the subVI's if anybody is interested..


cheers,
Thijs

[drs T Schrama]

Here's what I got so far.... the .ACQ-file info reader should work on all .ACQ files... but the data reader only works for 8 channel 16 bit data ... this is work in progress......

cheers,
Thijs