TDMtermite

The tdm_reaper is a C++ based library that decodes (encodes) the proprietary file format TDM/TDX for measurement data, which relies upon the technical data management data model. The TDM format was introduced by National Instruments and is employed by LabVIEW, LabWindows™/CVI™, Measurement Studio, SignalExpress, and DIAdem.

Data Format

Datasets encoded in the TDM/TDX format come along in pairs comprised of a .tdm (header) and a .tdx (data) file. While the .tdm file is a human-readable file providing meta information about the data set, the .tdx is a binary containing the actual data. The .tdm based on the technical data management model is an XML file and basically describes what data the .tdx contains and how to read it. The TDM data model structures the data hierarchically with respect to file, (channel) groups and channels. The file level XML may contain any number of (channel) groups each of which is made up of an arbitrary number of channels. Thus, the XML tree in the TDM header file looks basically like this:

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<usi:tdm xmlns:usi="http://www.ni.com/Schemas/USI/1_0" version="1.0">

  <usi:documentation>
    <usi:exporter>National Instruments USI</usi:exporter>
    <usi:exporterVersion>1.5</usi:exporterVersion>
  </usi:documentation>

  <usi:model modelName="National Instruments USI generated meta file" modelVersion="1.0">
    <usi:include nsUri="http://www.ni.com/DataModels/USI/TDM/1_0"/>
  </usi:model>

  <usi:include>
    <file byteOrder="littleEndian" url="example.tdx">
    ...
    <block byteOffset="0" id="inc0" length="1000" valueType="eFloat64Usi"/>
    ...
    <block_bm id="inc4" blockOffset="100" blockSize="7" byteOffset="0" length="4" valueType="eInt8Usi"/>
    ...
  </usi:include>

  <usi:data>
    ...
  </usi:data>

</usi:tdm>

and is comprised of four main XML elements: usi:documentation, usi:model, usi:include and usi:data. The element usi:include references the data file example.tdx and reveals one of two possible orderings of the mass data (.tdx):

either channel wise (<block>) - all values of a specific channel follow subsequently -
or block wise (<block_bm>) - all values of a specific measurement time follow subsequently -

ordering. The supported numerical data types are

datatype	channel datatype	numeric	value sequence	size	description
eInt16Usi	DT_SHORT	2	short_sequence	2byte	signed 16 bit integer
eInt32Usi	DT_LONG	6	long_sequence	4byte	signed 32 bit integer
eUInt8Usi	DT_BYTE	5	byte_sequence	1byte	unsigned 8 bit integer
eUInt16Usi	DT_SHORT	2	short_sequence	2byte	unsigned 16 bit integer
eUInt32Usi	DT_LONG	6	long_sequence	4byte	unsigned 32 bit integer
eFloat32Usi	DT_FLOAT	3	float_sequence	4byte	32 bit float
eFloat64Usi	DT_DOUBLE	7	double_sequence	8byte	64 Bit double
eStringUsi	DT_STRING	1	string_sequence		text

The XML element <usi:data> is basically comprised of five different types of elements that are <tdm_root>, <tdm_channelgroup>, <tdm_channel>, <localcolumn> and <submatrix>. The root element <tdm_root> describes the general properties of the dataset and lists the id's of all channel groups that belong to the dataset. The element <tdm_channelgroup> divides the channels into groups and has a unique id that is referenced by its root element. The <channels> element in <tdm_channelgroup> lists the unique ids of all channels that belong to that group. Finally, the element <tdm_channel> describes a single column of actual data including its datatype. The remaining element types are <localcolumn>

<localcolumn id="usiXY">
  <name>Untitled</name>
  <measurement_quantity>#xpointer(id("usiAB"))</measurement_quantity>
  <submatrix>#xpointer(id("usiMN"))</submatrix>
  <global_flag>15</global_flag>
  <independent>0</independent>
  <sequence_representation> ... </sequence_representation>
  <values>#xpointer(id("usiZ"))</values>
</localcolumn>

with a unique id, the <measurement_quantity> refering to one specific channel, the <submatrix> and its id respectively, the type of representation in <sequence_representation> - being one of explicit, implicit linear or rawlinear - and the <values> element, which refers to one value sequence, and the element <submatrix>

<submatrix id="usiXX">
  <name>Untitled</name>
  <measurement>#xpointer(id("usiUV"))</measurement>
  <number_of_rows>N</number_of_rows>
  <local_columns>#xpointer(id("usiMN"))</local_columns>
</submatrix>

that references the channel group in <measurement> it belongs to and provides the number of rows in the channels listed in <local_columns>.

Installation

The library can be used both as a CLI based tool and as a Python module.

CLI tool

To install the CLI tool tdmreaper do

make install

which uses /usr/local/bin as installation directory. On macOSX please first build the binary locally with make and install it in your preferred location.

Python

In order to build a Python module from the C++ code base the Cython package must be available, which may be installed via python3 -m pip install cython . Furthermore, the Numpy package is recommended to be able to pass arrays of data from the C++ kernel to Python. The makefile provides the target make cython-requirements to install all required Python modules. Finally, to build the Python extension tdm_reaper either locally or install it the targets make cython-build and make cython-install are provided. Hence, to install the Python module on the system simply do

make cython-requirements
make cython-install

that makes the module available to be imported as import tdm_reaper .

Usage

CLI tool

The usage of the CLI tool is sufficiently clarified by its help message displayed by tdmreaper --help. For instance, to extract the data decoded in the pair of files samples/SineData.tdm and samples/SineData.tdx into the directory /home/jack/data/:

tdmreaper samples/SineData.tdm samples/SineData.tdx --output /home/jack/data

The tool can also be used to list the available objects in the TDM dataset, which are i.a. channels, channelgroups and TDX blocks. For instance, to list all channels and channelgroups (without writing any file output):

tdmreaper samples/SineData.tdm samples/SineData.tdx --listgroups --listchannels

The user may also submit a filenaming rule to control the names of the files the channel(-group)s are written to. To this end, the magic flags %G %g, %C and %c representing the group id, group name, channel index and channel name are defined. The default filenaming option is

tdmreaper samples/SineData.tdm samples/SineData.tdx --output /home/jack/data --filenames channelgroup_%G.csv

which makes the tool write all channels grouped into files according to their group association, while all channelgroup filenames obey the pattern channelgroup_%G.csv with %G being replaced by the group id. The filenaming rule also enables the user to extract only a single channel(group) by providing a particular channel(-group) id in the filenaming flag. For example,

tdmreaper samples/SineData.tdm samples/SineData.tdx --output /home/jack/data -f channel_usi16_%c.csv --includemeta

will write the single channel with id usi16 to the file /home/jack/data/channel_usi16_A4.csv including its meta-data as a file header.

Python

To be able to use the Python module tdm_reaper it first has to be build locally or installed on the system. In the Python interpreter simply do:

import tdm_reaper

to import the module. The TDM files are provided by creating an instance of the tdm_reaper class:

# create 'tdm_reaper' instance object
try :
    jack = tdm_reaper.tdmreaper(b'samples/SineData.tdm',b'samples/SineData.tdx')
except RuntimeError as e:
    print("failed to load/decode TDM files: " + str(e))

After initializing the tdm_reaper object it can be used to extract any of the available data. For instance, to list the included channelgroups and channels:

# list ids of channelgroups
grpids = jack.get_channelgroup_ids()


# list ids of channels
chnids = jack.get_channel_ids()

As a use case, we have look at listing the ids of all channelgroups and printing their data to separate files:

import tdm_reaper
import re

# create 'tdm_reaper' instance object
try :
    jack = tdm_reaper.tdmreaper(b'samples/SineData.tdm',b'samples/SineData.tdx')
except RuntimeError as e :
    print("failed to load/decode TDM files: " + str(e))

# list ids of channelgroups
grpids = jack.get_channelgroup_ids()
grpids = [x.decode() for x in grpids]
print("list of channelgroups: ",grpids)

for grp in grpids :

    # obtain meta data of channelgroups
    grpinfo = jack.get_channelgroup_info(grp.encode())
    print( json.dumps(grpinfo,sort_keys=False,indent=4) )

    # write this channelgroup to file
    try :
        grpname = re.sub('[^A-Za-z0-9]','',grpinfo['name'])
        grpfile = "channelgroup_" + str(grp) + "_" + str(grpname) + ".csv"
        jack.print_channelgroup(grp.encode(),      # id of group to be printed
                                grpfile.encode(),  # filename
                                True,              # include metadata as fileheader
                                ord(' ')           # delimiter char
                                )
    except RuntimeError as e :
        print("failed to print channelgroup: " + str(grp) + " : " + str(e))

For a full example including more details see python/usage.py.

References

TDM

IEEE Standard and datatypes

Implementation

Languages

C++ 85.5%

Python 5%

Makefile 4.7%

Cython 2.8%

HTML 1.3%

Other 0.7%