innomar SBP smart - Get Values from NMEA Data

User’s Manual INNOMAR Parametric Sub-Bottom Profilers / SESWIN 93
Innomar Technologie GmbH (2023-01) 93
7.3.2 Get values from NMEA data
In most cases you will get NMEA-like navigation data. That is an ASCII text string starting with a
$-symbol and closing with carriage return and line feed. Values within the string are comma
separated. Examples for typical NMEA data delivered by GNSS receivers are given in appendix
A.18 on page 213.
Let’s assume you get 3 different NMEA sentences (ZDA, GGA, VTG) like in the following example
and you need position, time, speed and some information about GNSS data quality to be
recorded with your SBP data:
$GPZDA,145601.60,04,01,2007,+00,00*4C
$GPGGA,145601.80,5406.62954,N,01204.13627,E,2,05,3.0,26.12,M,38.87,M,5,0000*6D
$GPVTG,008.96,T,007.10,M,000.16,N,000.30,K,D*23
$GPZDA,145601.80,04,01,2007,+00,00*42
$GPGGA,145602.00,5406.62958,N,01204.13624,E,2,05,3.0,26.23,M,38.87,M,5,0000*6B
$GPVTG,340.83,T,338.98,M,000.08,N,000.16,K,D*2C
Position is to be found in the GGA string:
 Latitude: position 2
 Longitude: position 4
$GPGGA,145601.80,5406.62954,N,01204.13627,E,2,05,3.0,26.12,M,38.87,M,5,0000*6D
Time can be taken either from ZDA (UTC) or from GGA (UTC time of position fix):
$GPZDA,145601.60,04,01,2007,+00,00*4C
$GPGGA,145601.80,5406.62954,N,01204.13627,E,2,05,3.0,26.12,M,38.87,M,5,0000*6D
Heading and speed can be taken from VTG string:
 Track (heading): position 1; unit “T” on position 2 indicates true north heading
 Speed in knots: position 5; unit is given in position 6 (“N”)
 Speed in km/h: position 7; unit is given in position 8 (“K”):
$GPVTG,008.96,T,007.10,M,000.16,N,000.30,K,D*23
Information about GNSS data quality can be found in the GGA string, in some cases the antenna
height may be of interest as well to calculate values for tide correction:
 GNSS quality indicator position 6
 Number of satellites in use position 7
 Horizontal dilution of Position position 8
 Antenna height in meters position 9 (unit given in position 10, “M”)
$GPGGA,145601.80,5406.62954,N,01204.13627,E,2,05,3.0,26.12,M,38.87,M,5,0000*6D
For recording the values within the SBP data there are 8 so-called SIS strings available that can
hold up to 11 characters each. To get the values marked in the incoming NMEA data above into
the SIS strings as follows
SIS 1 Longitude (from GGA position 4)
SIS 2 Latitude (from GGA position 2)
SIS 3 Time (UTC from GGA position 1 or ZDA position 1)
SIS 4 Heading (calculated from LAT/LON; from VTG position 1)
SIS 5 Speed in knots (from VTG position 5)
SIS 6 GNSS position error (GGA position 8)
SIS 7 later for projected UTM-X; preliminary Longitude like SIS 1
SIS 8 later for projected UTM-Y; preliminary Latitude like SIS 2
!
At least the three first items are required as minimum information (LON, LAT, UTC).
For the above example you need to set the values according to the screenshot below.