GPS Spoofing

[Lon nan Gruagach]

Yes. It makes me wonder about gliding badges these days ...

And those widgets that insurance companies use to spy on your driving.

 

[JumbleDuck]

And those widgets that insurance companies use to spy on your driving.

Oo-er. That opens up some interesting possibilities!

 

[grumpy_o_g]

Spoofing a civilian GPS receiver to a fixed location is technically not very hard. You simply need to receive the signals from a handful of satellites at that location and re-broadcast them elsewhere at a high enough power to over-ride the true signals.
Generating the signals from scratch is not going to be beyond the means of the Russians who have developed their own system.

It's not something an amateur could knock up in a few evenings, but the principle is not hard.

Not knowing what's in civilian GPS systems I bow to your knowledge - I had assumed some basic logic to ensure that position didn't suddenly shift or that signals from all visible satellites agreed to at least some degree, etc. I know that's not on the chips but surely any serious piece of kit would have that in? Totally agree that it can be done and even the concept is pretty simple - it's the idea that it's a typical home electronics project that I'm struggling with.

 

[grumpy_o_g]

Year ago - twenty years? - gliding moved over to GPS loggers for badge and record attempts. Within months of the changeover, students somewhere had a proof-of-concept system running which let you out any track you liked into a GPS logger by spoofing the signal. Of course that was for a device about the size of a Garmin eTrex. Doing it to the Queen Victoria would be a tad more difficult.

Ah, the heady days of holding a foil-covered barograph drum over a smoking candle to soot it before trying to get it onto the barograph without smudging it; finding someone qualified to seal and sign it (who may, if they were kind, check that you had remembered to wind it up); carefully putting it in the back of the a/c without accidentally disconnecting the battery which was always right beside it; your heart stopping as the local instructor gives you a few last tips before attaching the cable and then casually asks if you've switched the barograph on...

Sitting in wave in what feels like absolute silence as you climb through 12,000 ft and are about to go onto oxygen desperately trying to hear if the barograph is still ticking...

Landing after you've got your height and even more carefully removing the barograph and trying to see if the trace is good through the crazed and smudged perspex; finding someone qualified to open the barograph and sign the trace and praying they don't smudge the trace when they sign it; taking your hard-earned trace and oh so carefully over-spraying it with it hair-spray before holding a lighter to burn off the volatiles in the hair-spray and seal the trace...

And please don't start me on dual Instamatics stuck to the side of the canopy and desperate chandelles to try and get a decent shot of the turning point...

Youth of today just don't know they're born

 

[GHA]

Maybe calibrate is the wrong word. When approaching an unknown coast I set an offshore waypoint over a prominent sea bottom feature (that has enough safe water)! When the GPS tells me I'm over it - or about to cross the feature, I watch the depth sounder (or take a some compass bearings if shore is in sight). Then I know what the GPS offset is (ie charted position error). Just an extra check!

Sounds sensible but how do you know the charts have their datum offset by the same amount further in?

I like having google satellite images as chart files to check, yet to find them less than accurate enough though heard in some small islands in the middle of nowhere some data might be missing.

The excellent but slightly clunky Ge2Kap has an option to adjust the datum ->

https://onedrive.live.com/?authkey=...F71B!1381&parId=E42CE519717DF71B!1339&o=OneUp

 

[laika]

It makes me wonder about gliding badges these days ...

I knew that flying squirrels were a thing but gliding badgers?

 

[JumbleDuck]

Ah, the heady days of holding a foil-covered barograph drum over a smoking candle to soot it before trying to get it onto the barograph without smudging it; finding someone qualified to seal and sign it (who may, if they were kind, check that you had remembered to wind it up); carefully putting it in the back of the a/c without accidentally disconnecting the battery which was always right beside it; your heart stopping as the local instructor gives you a few last tips before attaching the cable and then casually asks if you've switched the barograph on...

I bought the ink conversion for mine. No smoky Joe for me!

Sitting in wave in what feels like absolute silence as you climb through 12,000 ft and are about to go onto oxygen desperately trying to hear if the barograph is still ticking...

A friend of mine got into wave over the Cheviots and realised that he hadn't turned his barograph on. So he trimmed the glider out (Skylark 2), opened the canopy, undid his straps, turned round to kneel on his seat (all this at about 5,000' AGL) reached into the fuselage and turned it on before turning round, sitting down, strapping in, closing the hatch and flying on. Still didn't make gold.

Landing after you've got your height and even more carefully removing the barograph and trying to see if the trace is good through the crazed and smudged perspex...

I did my 300km triangle in under five hours in a Pirat only to find that the barograph arm had a bend in it and lifted the pen off the paper every time I got above 3,500'. The OO reckoned it was proof that I didn't land, but I never got round to claiming, so I am still just a Silver C. I'd like to go back, but it's all so bureaucratic now.

 

[AntarcticPilot]

Sounds sensible but how do you know the charts have their datum offset by the same amount further in?

I like having google satellite images as chart files to check, yet to find them less than accurate enough though heard in some small islands in the middle of nowhere some data might be missing.

The excellent but slightly clunky Ge2Kap has an option to adjust the datum ->

https://onedrive.live.com/?authkey=...F71B!1381&parId=E42CE519717DF71B!1339&o=OneUp

Datums are tricky, especially in remote parts of the world. They were bad enough in the UK 20 years ago!

There are basically several kinds of datum. The simplest, used in many remote places, is that the original surveyors determined a position to the best of their ability (usually using star sights with a theodolite) and then said, OK, this nail we've hammered in this rock is at EXACTLY the position we observed with our star sights. Of course, the star sights had an error built in even if they were accurately observed and correctly computed, so that kind of datum has errors of a few hundred metres. Usually the legend of the map or chart will say something like Datum: Astro observation at X lat, Y long by Lt soandso in 1850.

The second, used in most advanced or colonial countries until the advent of GPS, is that you have a whole survey network with angles between the various survey marks measured. Many of the survey marks will also have astronomical observations, some using full-scale observatories, so the position fixing is very precise. The vast quantity of survey observations are then reduced to a list of positions of each survey point. This was done for the UK in 1936, using electromechanical calculators, and is the source of the original OSGB36 datum. You then say that each survey point is at precisely the position computed, and work from there. The OSGB36 network, while a tremendous achievement for the time, has several deficiencies, including a few places where if you start from one survey point you'll get a different position than if you start from another!

Neither of these types of datum are globally useful, and when astronomical observations using Long Baseline Interferometry started to produce measurements of the separation of radio telescopes on different continents accurate to millimetres, global datums were found to be necessary. They already existed, but were matters of academic interest for most people until this point. A global datum is basically a specification of an ellipsoid of revolution (the Earth is a sort of squashed melon shape) and the precise orientation of this spheroid WRT the surface of the Earth. WGS72 was the first in widespread use, this is insignificantly different from WGS84 (WGS84 added a few decimal places of precision to the parameters). Satellite systems use these global datums, and mapping using survey based datums was transferred to the ellipsoidal datum - in the UK this took place in ABOUT 1995 - 2010.

Finally there is another, yet more precise type of datum which takes account of continental motion, polar wandering and other geophysical effects. This is the ITRF series of datums - there tends to be a new one every year. For practical purposes these are indistinguishable from WGS84, but if you want millimetre precision and to measure continental drift, they are what you use!

 

[dolabriform]

Datums are tricky, especially in remote parts of the world. They were bad enough in the UK 20 years ago!

There are basically several kinds of datum. The simplest, used in many remote places, is that the original surveyors determined a position to the best of their ability (usually using star sights with a theodolite) and then said, OK, this nail we've hammered in this rock is at EXACTLY the position we observed with our star sights. Of course, the star sights had an error built in even if they were accurately observed and correctly computed, so that kind of datum has errors of a few hundred metres. Usually the legend of the map or chart will say something like Datum: Astro observation at X lat, Y long by Lt soandso in 1850.

The second, used in most advanced or colonial countries until the advent of GPS, is that you have a whole survey network with angles between the various survey marks measured. Many of the survey marks will also have astronomical observations, some using full-scale observatories, so the position fixing is very precise. The vast quantity of survey observations are then reduced to a list of positions of each survey point. This was done for the UK in 1936, using electromechanical calculators, and is the source of the original OSGB36 datum. You then say that each survey point is at precisely the position computed, and work from there. The OSGB36 network, while a tremendous achievement for the time, has several deficiencies, including a few places where if you start from one survey point you'll get a different position than if you start from another!

Neither of these types of datum are globally useful, and when astronomical observations using Long Baseline Interferometry started to produce measurements of the separation of radio telescopes on different continents accurate to millimetres, global datums were found to be necessary. They already existed, but were matters of academic interest for most people until this point. A global datum is basically a specification of an ellipsoid of revolution (the Earth is a sort of squashed melon shape) and the precise orientation of this spheroid WRT the surface of the Earth. WGS72 was the first in widespread use, this is insignificantly different from WGS84 (WGS84 added a few decimal places of precision to the parameters). Satellite systems use these global datums, and mapping using survey based datums was transferred to the ellipsoidal datum - in the UK this took place in ABOUT 1995 - 2010.

Finally there is another, yet more precise type of datum which takes account of continental motion, polar wandering and other geophysical effects. This is the ITRF series of datums - there tends to be a new one every year. For practical purposes these are indistinguishable from WGS84, but if you want millimetre precision and to measure continental drift, they are what you use!

WOW, thanks for that. I feel I have learnt something useful today!