|Chesapeake Times, Vol 2 | July 2020|
NMEA 0183 sentences are text strings that conform to the NMEA 0183 format specification. These are most commonly used in sending data over digital serial protocol links. These sentences are human readable and can be recognized easily because they start with a “$” character and end with a “*” character. The sentences can be received by a computer and logged to a text file using anything from a simple terminal program to CTI’s Single Beam server.
Here is a sample set of sentences:
The sample was generated by CTI’s NMEAWiz software. It is capable of simulating a variety of NMEA 0183 data.
Supported NMEA 0183 Sentences
DBT, DPT, DBS
GGA, GLL, RMC
GGA, RMC, ZDA
HDT, HDG, RMC (Course Made Good), VTG (Course Made Good)
SonarWiz requires at least time, date, position, and depth for the successful import and processing of Single Beam sonar data. The user should configure their devices such as GPS and Depth Sounder to output a combination of these strings in order to provide the required data. We recommend using the RMC string since it covers 3 out of the 4 requirements (position, time, and date). In addition to the RMC string a DBT or DPT string should be provided. We recommend these be sent at a rate of 1 Hz or faster.
Previous versions of SonarWiz required the presence of heading information. This is no longer a requirement as of SonarWiz V7.06.04. If heading information (in the form of a HDT, HDG, RMC, or VTG string) is not present in a log file, simply leave the “Adjust soundings for Roll and Pitch” checkbox unchecked in the Single Beam Import Window as shown below. In addition to NMEA formatted log files, this setting applies to the other Single Beam import data types as well.
|Sometimes a user works with equipment that is not configured correctly or is incapable of providing all of the information necessary. This commonly takes the form of missing date information. This can happen when a GPS is configured only for sending GGA sentences. In order to process this data the user would have to provide a manual date by manually inserting a ZDA sentence at the beginning of a data log file. This can be tedious when working with a survey with more than a few data log files. In order to assist the user, CTI has added detection of the missing date information during import. Upon detecting missing date information SonarWiz will now ask the user for the date information (pictured below).|
|The user can choose to use the date information for each additional file freeing them from the need to repeatedly enter the same date.|
In summary, successful processing of NMEA Single Beam sonar data depends on having time, date, position, and depth data present in the data log files. SonarWiz has been improved to allow for missing date and heading information so that the user can easily process their surveys.
– Christopher Favreau, Program Manager