Purpose of this technical note

To process the data collected by the Signature VM system, it is sometimes useful to access the unprocessed data stored in the Signature VM recordings. This allows data processing beyond the capabilities of Signature VM Review.

Signature VM data format

The Signature VM datafiles (.SigVM ) are zip archives that store the Nortek ad2cp instrument data, and navigation information. The SigVM file can be opened using, for instance, 7Zip, or with the standard Windows Explorer. (To open the SigVM zip archive using Windows Explorer you will need to change the file extension to”.zip”.)

Figure 1: SigVM file opened in 7Zip

The .SigVM file contains an ad2cp file (with associated xml configuration file, containing the program option settings from the time of recording) and one or more files that contain navigation information.

Additional information about the layout of the ad2cp file can be found in the Integrators guide:
Integrators Guide – Signature – Nortek Support Center (nortekgroup.com)

There are two possible formats for the navigation information:

• anpp:
  
  This is the binary format supported by the Advanced Navigation GNSS; for the Signature VM (Coastal) system this is the default. For details about the Advanced Navigation GNSS Compass, see https://www.advancednavigation.com/inertial-navigation-systems/satellite-compass/gnss-compass/
  
  To decode the binary structures in this file, see the  GNSS Compass Reference Manual, section Advanced Navigation Packet Protocol.
  
  For navigation purposes the most relevant package is the “System State package” that contains all the navigation information. Examples of the decoding can be found in the GNSS Compass SDK, GNSSCompassSDK_v7.0.zip.
  

  
  (Please be aware that Advanced Navigation updates and modifies their documentation, software and website with some regularity, so the links provided may no longer be valid by the time of reading. In that case you may need to search Advanced Navigation’s web-site, or follow links from the GNSS compass page.)

  Note that another option to convert the binary anpp format is to use Advanced Navigation’s CompassManager java application. Using CompassManager, the binary anpp file can be converted to a directory containing several plain text files, as well as some csv-files and a kml-file. One of the csv-files corresponds to the “System State package” mentioned above.
  
  

• .nmea: 
  

  This is standard NMEA according to the IEC61162 with IEC61162-450 Time tags; figure 2 shows an example.
  The time tags, for example “\c:1601731756.026*44”, start with \c, and end with * and a checksum.
  1601731756.026 is time in the Unix timestamp format (the number of seconds since the start of the Unix epoch, 00:00:00 UTC on 1 January 1970).

Figure 2: Typical NMEA IEC61162-450 message