GPS errors

[asteven221]

I have a Garmin 128 gps which is linked to Seapro Lite on a laptop and a problem has appeared and I can't figure out what is causing it. All has worked fine for ages so its a fault that's developed rather than with the installation itself. Basically the position shown on Seapro and the position on the GPS are different, but only the seconds figure. The degrees and minutes figures always match. The difference is between about 6 to as much as 20 seconds. I have tried looking at the raw NMEA data on Seapro and it confirms that Seapro is displaying exactly what seems to be getting transmitted by the Garmin 128 GPS, so I reckon Seapro is not the culprit. I have compared the position information when the boat is stationary and moving with the same results. This is a bit bizarre. Has anyone heard of this type if problem? Any advice is appreciated. Thanks.

 

[Dipper]

I don't know whether you need to do this or whether it is automatic but are they both set to the same map datum?

 

[thalassa]

Or one is set to degrees-minutes-seconds and the other to degrees-minutes-decimal?

 

[Pye_End]

Perhaps a data smoothing induced error?

 

[pau1gray]

I'd start to look as dipper suggested that the GPS set is set up to display WGS84 positions and not somthing like ED50 positions. The NMEA string will (should) always be set to WGS84 so Seapro is doing it thang correctly!

 

[Bilgediver]

This is what I believe....You need to set all to decimal or all to minutes and seconds. This frequently happens where a GPS is linked to a DSC Radio where they are not both set up the same.

 

[tome]

GPS 128 NMEA output will be whatever datum it is currently set to, not necessarily WGS-84 so listen to dipper

Giveaway is a constant error whether moving or not - well done with a clear description of the problem. Go to the Nav menu and check the current datum

 

[asteven221]

Thanks everybody for the help. The gps is set for WGS84, but I will double check everything - especially the chart datum and the degrees, minutes, seconds vs degrees, minutes and decimal. Incidentaly the error is apparent when the boat is stationary or moving. I won't be down at the boat for a couple of weeks now as I am off to sunnier climes on Friday, but as soon as I get back I will check everything out. Thanks again.