Interpretation of Simrad GL Telegrams
Echosounder data files in .EK5 and .DGn formats will normally include the raw or pre-processed GPS navigation string as generated by the GPS unit in "GL" type telegrams.
For example, GPS data from a Simrad Ex500 are pre-processed and output in a navigation telegram. The Ex500 accepts as navigation input NMEA 0183 (or other communication protocol) telegrams via a serial or Ethernet connection to a navigation instrument such as a GPS. You can specify which data elements from the input telegrams are made available to the EK500 geographical position (navigation) telegrams (GL telegrams). Consult the Navigation menu section of your Ex500 manual for details.
Echoview "parses" the Navigation (GL) telegrams to extract latitude and longitude and will successfully extract latitude and longitude from telegrams that meet one of the two following formats:
[???.???,]LLMM.MM,N,LLLMM.MM,W[???.???]
where [???.???] represents any number of text characters that may or may not be present, and followed or preceded by a comma as indicated. "N" is S or N for south or north latitudes, LL or LLL are degrees of latitude and longitude and "W" is E or W for east or west longitudes, MM.MM are decimal minutes of latitude and longitude (and there is no restriction on the number of figures after the decimal point). For example. from "6345.456,S,14345.456,W,25.0,0.2,1" latitude 63 45.456 S and longitude 143 45.456 W would be extracted.
(This format should successfully extract latitude and longitude from a range of standard NMEA 0183 navigation telegrams.)
[???.???] S LL MM.MMM E LLL MM.MMM[???.???]
where [???.???] represents any number of text characters that may or may not be present, "S" is S or N for south or north latitudes, "E" is E or W for east or west longitudes, LL or LLL are degrees of latitude and longitude and MM.MM are decimal minutes of latitude and longitude (and there is no restriction on the number of figures after the decimal point). For example, from " 3/30/97 4:17: 9 S 42 52.782 E 147 20.476 25.0 0.2 92.7 1" latitude 42 52.782 S and longitude 147 20.476 E would be extracted.
(This format suits the Magnavox MX 1107 GPS and similar telegrams where the Ex500 was not set to extract and output the individual navigation elements.)
There are many possible formats for the EK500 navigation telegram depending on both the navigation instrument used and the EK500 setup. Where possible, you should set the navigation output of your Ex500 to match one of the above formats. If for any reason it is not possible to match one of these formats Echoview Software will consider adding a new format to Echoview.
Please contact Echoview support and provide a sample data file including navigation telegrams in the format you need to use and if possible a specification for the format.
If an incompatible format is used no data will be displayed in the cruise track view.
Complete GPGGA strings
If a complete NMEA standard GGA string is in the Simrad GL telegram, then in addition to latitude and longitude Echoview will read GPS time and altitude from the string. These can be output with line exports and both are interpolated to obtain values for individual pings.