Author Topic: AIS Newbie - Timestamps from the NMEA Sample  (Read 206 times)

pwillemann

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AIS Newbie - Timestamps from the NMEA Sample
« on: 05 April, 2017, 06:51:26 pm »
I have been asked to retrieve AIS messages from the NMEA Sample data (http://www.aishub.net/nmea-sample.php) which contains about 3 minutes of data.  I used a third party program https://github.com/dma-ais/AisLib and can successfully get the AIS messages.  For now, I am only interested in AIS message #1.  I need to extract some fields from the message and send them to another program.  This program requires a timestamp and I am not really sure how to get timestamps from the sample data.  Am I suppose to use an AIS message #4 to get the basic time and then use the UTCSec field in the AIS message #1?  What if my data set doesn't immediately have an AIS message #4?  Am I suppose to read the sample data twice?  Any help would be appreciated.


Thanks
Phil

malcolmh

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Re: AIS Newbie - Timestamps from the NMEA Sample
« Reply #1 on: 07 April, 2017, 09:13:16 am »
Full UTC date/time data is to be found in Base station reports, of which there are a few in the sample. Ship position reports only give the seconds after the UTC minute in their timestamps. To determine the full time, it will be necessary to fast forward to the Base Station report to get the date, hour & minute for the preceding messages.