1cm GPS accuracy? Not really on a boat but...

[The Q]

Some clever bods have now produced a live GPS spoofing website so you can see where trouble lies -

Live GPS Spoofing Tracker Map

That perfectly ties up with what I saw on flight radar..

 

[boomerangben]

The last edition of the RIN's Navigation News quoted a report saying that aviators in the United States have been advised not to rely on GNSS for positioning owing to the the level of signal spoofing and jamming that has been detected.

Wow that’s going to send shockwaves through that community. As I understand it, the US has fully embraced GNSS approaches.

 

[Bilgediver]

I too had RDF, which probably isn't a surprise as I was a radar Technician.. used it quite a lot in the Hebrides. Not too many buoys, but a fair amount of lighthouses I could get a fix on.

If you remember those old RDF sets as well as the long wave beacon frequency had the medium wave receiver also. This was not for entertainment. In the olden days if doing a great circle Japan to Panama in the winter when no sky and no stars for 21 days then how do you think we found our way around the great circle My face lit up when I could sit on deck with my we little Japanese tranny and listen to a Vancouver station and wish I was there. I have seen 2 UE used for this as wel




In the north sea when oilfield drilling we had various problems and one of those was being in the right place. This we could do down to very fine limits The system used was to put a GPS receiver on a nearby fixed installation which took the GPS signal position and compared it to the known position. The difference was transmitted to the nearby floating rig and inserted into its system so that a corrected position was shown.

In later years when GPS got better we used a system where the position of the well was compared to the position of the rig and this controlled the azimuth thrusters to keep us centred over the well.

Mind you no matter how good these systems are there is nothing that replaces a good helmsman when operating in close quarters because then the position of the antennas related to the ends of the vessel makes a difference too.

One thing that should be considered when viewing tracks on Marine Traffic and on Flight radar 24 is how these sights operated. I have a pilot son and watching these sights can give anxiety due to problems in the system when he suddenly disappears in the south Atlantic..


The problem is that much of the data used on these systems is data received from volunteers operating receivers at their own addresses. The equipment includes an internet gateway. Unfortunately there is not a comprehensive net of these stations so a few gaps and in the case of stations commercially feeding data they too can not always cover a full area It is not unusual to see an aircraft track where the station has lost track of the plane then later locked on again. The tracker assumes the plane flew straight between those two points when in fact it could have flown out and back a much further distance hence the wrong speed.

IF you go to the site below then you can see where the tracking signals are being received. AIS is based on a ham system.

aprs.fi – live APRS map

 

[MADRIGAL]

In the north sea when oilfield drilling we had various problems and one of those was being in the right place. This we could do down to very fine limits The system used was to put a GPS receiver on a nearby fixed installation which took the GPS signal position and compared it to the known position. The difference was transmitted to the nearby floating rig and inserted into its system so that a corrected position was shown.

In later years when GPS got better we used a system where the position of the well was compared to the position of the rig and this controlled the azimuth thrusters to keep us centred over the well.

At the time of the Flinders Islet yacht race in 2009, drilling under Sydney Harbour for the new desalination plant had been suspended because dilution of precision, a measure of GNSS inaccuracy, had become too high. A yacht sailed too close to the islet, which was a mark in the race, and broke up on a reef with the loss of two crew. The investigation report blamed the accident in part on exclusive reliance on GNSS for positioning, inadequate lookout being kept, and likely GNSS inaccuracy at the time of the accident.

 

[Bilgediver]

All sorts of things can give problems.vWe have stiffest that row in the river Forth. One team recently went to one of the legs of the Forth Bridge which is four columns of steel on roun masonry basses. His intention was to draw a four leaf cover on Strava . This is a tracking app used by athletes. The result was the oddest shape which upset him after all his efforts. The steel work I. Our bridges can do more than just this and there was thousands of tons above him

 

[AntarcticPilot]

All sorts of things can give problems.vWe have stiffest that row in the river Forth. One team recently went to one of the legs of the Forth Bridge which is four columns of steel on roun masonry basses. His intention was to draw a four leaf cover on Strava . This is a tracking app used by athletes. The result was the oddest shape which upset him after all his efforts. The steel work I. Our bridges can do more than just this and there was thousands of tons above him

Yes; the accuracy of GNSS in Hong Kong is extremely variable, as you're often surrounded by steel framed tall buildings.