Accuracy GPS records

Whilst we are rightly asked not to comment on the events in that disputed waterway, our PM has turned vicious and threatens a new, more serious, turn of events. These are assumed to be GPS records showing where the boats were. I do not wish to condemn the response in advance but foresee that it will be that we have falsified these records - that is if the new approach is even considered coming as it does from soft and cuddly Government.
Whilst I have used GPS in the wild, I have no idea if it is possible to forge the reports - without, of course, resorting to Photoshop-type software. Given that our ferocious and wily PM considers it a stern measure, I assume it is cast-iron evidence.
Others here may think differently?
To establish the position of an object via GPS only could be open to debate. If, for example, you wanted to show that a particular vessel was in the wrong lane exiting Southampton Water, you might want to link the GPS record to your radar record or even a photographic record which could be triangulated to give a precise position.
The GPS record is typically logged onboard the recording vehicle/vessel although it can be transmitted by datalink radio to another location and recorded there. Without claiming any knowledge of how it is employed by RN, an obvious way that this might be used is that all vessels transmit their current location and the "flagship" uses this information to coordinate movements. In this case, every vessel would probably log the GPS trace of every other vessel whose signal it recieved.

As to how easy it would be to fake a record - well you only really need a text editor:
WGS 84
Altitude is in Feet
Reserved 3
0,2,255,Track Log - 06/04/2006 07:46:18 ,0,0,2,8421376

52.436692, -1.931353,0, 571.0,38814.7346991, 07-Apr-06, 17:37:58
52.437483, -1.932073,0, 593.0,38814.7348032, 07-Apr-06, 17:38:07
52.438358, -1.932703,0, 558.0,38814.7348958, 07-Apr-06, 17:38:15
52.439203, -1.933337,0, 548.0,38814.7349769, 07-Apr-06, 17:38:22
52.440065, -1.934067,0, 547.0,38814.7350579, 07-Apr-06, 17:38:29
52.440907, -1.934812,0, 544.0,38814.7351389, 07-Apr-06, 17:38:36
52.441725, -1.935490,0, 540.0,38814.7352199, 07-Apr-06, 17:38:43
52.442455, -1.936320,0, 538.0,38814.7353125, 07-Apr-06, 17:38:51
52.443292, -1.936942,0, 529.0,38814.7354051, 07-Apr-06, 17:38:59
The columns are latitude, longitude, altitude and time.

As you can see from this one minute's worth of data, It would be quite simple to edit the numbers. If it wasn't done very cleverly, there would be obvious jumps from one location to another. However, if it was done well I don't see how you could tell.

I would conclude that it is potentially easy to spot a bad fake but impossible to spot a good one. I don't see it can really prove anything.
Pretty much every form of datalogging generates a text file of some sort, even if it's encrypted.
On the other hand, something like a video tape of an operations plot table would be much more difficult to fake convincingly.

Just my opinion based on my civilian use of GPS.

(Did you spot the errors in the file? It's been tampered with.)
There are also all sorts of interesting things one can do to unprotected receivers in terms of jamming and spoofing (ie causing it to read a false position). Protected receivers are available but they are expensive and traditionally slide to the bottom of the priority list.

In view of the news I'll leave the implications of being able to cause GPS to read a false position as an exercise for the reader. I'd also point out that a proper analysis of such data requires details of the receivers used and their anti-spoofing abilities, and indeed whether or not it could detect such spoofing if present.


According to the beeb, we've got photographic evidence to back up GPS readings.

As to errors in the file EX_STAB, is it that the time intervals between readings aren't consistent, or am I on completely the wrong track?
Stooge said:
According to the beeb, we've got photographic evidence to back up GPS readings.

As to errors in the file EX_STAB, is it that the time intervals between readings aren't consistent, or am I on completely the wrong track?
No, the timestamp in the file header doesn't relate to the timestaps of the position recordings. Also, if that was the beginning of the file, the GPS would have been doing well to initialise and get a halfway consistent altitude that quickly at that speed.

Exciting heh?

Try the coordinates in Google Earth and you can see which side I was sitting. The Altitude result is not bad considering the terrain.
Or just cheat and follow this link.
The thing about GPS jammers is just how cheap they are to get your hands on. They require a very low power to cause an awful lot of damage to either your signal or your location readings. As strange pointed out there are systems that are used to stop this happening. The Bowman kit for example has the ability to have a code input into it to stop spoofing, I for one however have never seen this used.

They reckon when the we went into Iraq there were 6-10 high powered jammers that could screw with the missile guidence systems. However not very many were found at all and the onces that were found were still in the packaging.

Also there was approx 100 on order that were to be delivered about 2 months after we went over the border.

TRL are a UK based company that deal with this kind of equipment.
The accuracy of a GPS position,shown on a map,will depend as much,upon the accuracy of the map data.I imagine that the Iranians will be using their own maps,adjusted for the truth,which will show the same GPS positions,as being inside their territorial waters?
With reference to the post above which I won't quote, perhaps at present we ought to discuss this on a hypothetical and technical basis rather than relating it to current negotiations?
EX_STAB said:
Anybody worked out my speed yet?
Naughty boy! Weren't looking for a bed there, were you?

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