Odd odometer

[Taniwani]

I found the TZT2 odometer (and the trip counters) accumulating miles while stationary. This is particularly bad when the GPS reception isn't great. But even with good reception it kept going up slowly. It seems there is no threshold on SOG as the usual small SOG of 0.1 - 0.2 KTS that all my GPSs are showing, is being counted.

Setting SOG/COG smoothing to 10 secs slows the counting a bit but doesn't really fix it.

The remedy I found in the track settings! Setting track to distance and the distance to the smallest possible other than zero, (0.01Nm = 19m), fixes the problem and the odometers stop counting up. With the track setting on any time interval it will creep up, as there is always a slightly different position at the next time interval.

I can live with this track setting, but think the odometers should have their own filter settings.

 

[Johnny Electron]

Thanks for the feedback. I will pass that to product development. I agree the distance settings is much better to use for tracks, otherwise if setup for "time" you will drop trackpoints in a big pile just sitting at the dock. Thanks for the post.

 

[Johnny Electron]

Talking to the engineers they suspect your GPS data quality is low. This might be because something in your area is providing interference or the placement of the GPS on the boat is within a transmitting source which can damage the front end receiver of a GPS. You might want to look at your HDOP of your GPS status. Normally you want 1.9 or lower.

 

[Taniwani]

In a way that is true, as the boat is on the dry under the airport runway some 200 ft above, so the view is to lower satellites only. But when I looked it was locked on some 7 satellites anyway.

So yes, I have seen the position vary within 10-12 meters and I'm sure that will be much less once I'm out in the open.

I don't think the GPS has a problem, with the two TZT2s I have four to choose from. Not surprisingly the built in units in the MFDs are a bit worse than the main GPS, a Thrane LT-1000 or next best the AIS transponder also with an external antenna. But all of them get a fix within a minute from powering on.

My old MFD didn't have that problem and was running a rather nice and reliable odometer, but it was from a time when GPS still had SA and a rather inaccurate position. So I'm sure they didn't clock up a distance, of you hadn't moved a 100 yards or so.

With respect to the TZT2 I don't know what limit on distance needs to be reached between two samples before it counts up, but it seems too sensitive, too unfiltered.

Given that odometer behaviour follows track settings, it appears to me, that when using time intervals, any distance, however small between the two samples is counted. So I doubt that the odometer wouldn't slowly count up even with an open sky view unless there is a programmed threshold of a few meters.

On the other hand, setting tracks to distance with the smallest possible distance of 0.01NM or about 19 meters, stops it counting up completely, proving that there is no position change of more than 19m.

At 0.01 NM track interval I would reach the 30000 track-point limit sailing just 300 miles, so I I plan to actually set track distance interval ten times higher, to 0.1NM. And I would expect the odometer to go along with that as well, and only count if I really moved more more than 0.1 miles. That is maybe a bit coarse but better than counting when stationary.

I am happy, if you can confirm, that my observation, that the odometer counting is coupled to the track algorithm is correct. Then I know it is working for me.

 

[Johnny Electron]

The unit is programmed to update the ODM if moving more than 1 yard per second based on the distance/time formula. If you get a good GPS fix it should work for you. I will pass on your comments.