No tracks when own ship data supplied by AIS
No tracks when own ship data supplied by AIS
May 05, 2019 01:19PM
Had to reconstruct some of my electronics after a direct lightning strike. One of the casualties was a (now discontinued) SeaCAS unit that supplied both GPS sentences and AIS sentences; this device was feeding a laptop running PolarView.

Replacing the SeaCAS, I have connected this laptop instead to pilot plug output from a Class-A AIS transponder (Furuno FA-100). In addition to AIS target information, this supplies Own Ship information in the form of AIVDO sentences. The data is good and Polar View correctly shows own ship position, heading, course, and speed. But there are no "bread crumbs" behind the ship, even though tracking is on.

Plugging a regular GPS puck (BU-353) into the laptop instead of the AIS feed does place tracks behind the ship. So it would appear that track points are dropped when own ship data comes via GPRMC, but not when it comes via AIVDO.

Is there a setting I am missing, or is this a bug?

-Sean
m/y Vector
lying Charleston, SC
Re: No tracks when own ship data supplied by AIS
May 05, 2019 01:36PM
1. As a quick test, could you please open Preferences->Data panel, and select "Time source" value "Operating system"

2. If this does not turn on tracking, could you please collect and attach some sample data including VDO sentences.

The easiest way to do so is to open NMEA Terminal while data is arriving, let it run for a few minutes and then copy and paste several screens worth of NMEA sentences into a plain text file.

--
Polar Navy Support



Edited 1 time(s). Last edit at 05/05/2019 01:38PM by Polar Navy Support.
Re: No tracks when own ship data supplied by AIS
May 05, 2019 07:24PM
Yes, it appears that setting Time Source to OS makes the tracks work again. Thank you very much.

Would you still like me to collect some VDO data?

-Sean
Re: No tracks when own ship data supplied by AIS
May 05, 2019 08:29PM
This seems to work as designed. VDO sentences do not contain time information.

For this reason, GPS NMEA messages are preferable for navigation. While system clock may work as a substitute, it does not match with the actual location messages quite as well.

--
Polar Navy Support
Re: No tracks when own ship data supplied by AIS
May 06, 2019 10:28AM
Thanks, that makes sense.

Our main plotter, at the helm, does have several NMEA inputs including two different GPS sources along with the AIS. This port feeds a separate laptop, away from the helm station, for the off watch to be able to follow along and provide a second set of eyes, and serves as a backup in case the main plotter PC or software suffers an under way crash or hang.

The backup laptop has just a single NMEA port. The SeaCAS unit provided both GPS and AIS sentences on one port and so was an ideal device for this backup use. I'm sorry to see it go. Our options in its absence were to supply the backup machine with a straight GPS signal, or use this extra feed from the AIS. We find having the AIS targets visible on the backup machine worthwhile, so we'll just live with the time source limitation.

-Sean
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