TomTom: use for meauring train speed

[Sox]

This may have been asked before but has anyone tried taking a satnav on a train journey from the point of view of measuring their ground speed.

Alternatively, does anybody know an app that can be downloaded onto an ipad* which does a similar thing (maybe even provide a journey/data log function).

The "itrain app"?

*something I have found out but, in case anyone is thinking of buying an ipad, the 3G one (not the wifi-only version) has GPS installed as part of the 3G chip set. For wi-fi only ipads, apparently stand alone blue-tooth GPS devices can be purchased.

 

[oversteer]

GPS works on a train, although you might need to sit near a window.

Your TomTom will get very confused though and jump from road to road alongside the tracks !

There are a number of "speedometer" apps available and you could use MotionX (or any similar sport-tracking software) as a datalogger.

 

[johnnyp_360]

I tried that with my old Nokia GPS. It said I was travelling at 110mph on the GEML between Stowmarket and Diss. It too got confused and jumped to roads near the track.

 

[tsr]

I reckon a hikers' or cyclists' satnav might be better, as it may not expect you to stick as rigidly to any given route, or might find paths to follow that are closer to the railway line, if it's surrounded by fields, for example. I can't recommend any particular model, I'm afraid.

 

[scotsman]

GPS is generally fairly accurate until you go round a curve, and the GPS takes the chord of the curve - giving an artificially high reading

I've found, personally, that my Blackberry's GPS is very good for finding my speed

 

[deltic1989]

There are a number of "speedometer" apps available.

Some are better than others though. I had one on my HTC wildfire s, that tried to tell me that a 158 was doing 140mph whilst slowing to stop at Lowdham. Got a better one now though thats more accurate.

 

[PaulLothian]

I use my Garmin eTrex quite often for this purpose - as a walker's GPS device it's not tied to preset routes, and measures curved courses accurately. As far as I can tell, it refreshes often enough to measure round curves - at least there is no significant difference between milepost distances and GPS distances even on bendy routes.

It does get confused by tunnels, but picks up the signal and works out the sums as soon as it can. Only gap I have noticed in functionality is a blank in the middle of the track of your course. Far easier these days than trying to spot non-existent mile posts!

 

[Mojo]

I use an iPhone App simply titled 'Dashboard.' Takes a while to set up but gives fairly accurate readings on HS1. Of course I wouldn't rely on it for anything official, but it gives a good idea.

 

[Mike C]

For a good price and far more accurate than anything I've used on my iphone, is this:
http://www.holux-uk.co.uk/holux-gpsport-245.php?it=173&gclid=CP_t1vn3s60CFYEmtAodEnarWA

It also data logs the journey and you can plot speed vs distance, or speed vs time graphs and also plot the route on google earth. It can take a few moments to lock to a signal, but once it's got it, it holds on fine.

A quick video I took of it working once:
http://www.youtube.com/watch?v=yDLme4eGE5A

 

[Minilad]

I find MotionX on an iPad to be pretty accurate

 

[Zoe]

Not all GPS devices though take elevation into account when calculating speed so if this is the case and you are not dead level then the speed displayed won't be your true speed.

 

[156441]

I've used a cycle app called 'Cyclemeter' on a Altrincham - Oxford Road service once. Gave fairly accurate results, plots your course on google maps and measures elevation accurately.

Bearing in mind google maps now seems to have most train lines on it now it works like a treat!

 

[Zoe]

I've used a cycle app called 'Cyclemeter' on a Altrincham - Oxford Road service once. Gave fairly accurate results, plots your course on google maps and measures elevation accurately.

I'm not questioning the accuracy of the elevation itself but the fact that change in elevation is taken into account when calculating speed. As far as I know not all GPS devices do this.

 

[Bevan Price]

The Railway Performance Timing Guide discusses use of GPS to measure speeds. See pages 14 to 16 of the free pdf. file download available at:

http://www.railperf.org.uk/index/timing-guide

Note that satellite reception is usually poor on Voyager type trains, and less than ideal on Pendolinos. Don't rely on 100% accuracy everywhere. You lose reception in tunnels, and sometimes where there are lots of trees - the GPS can try to "catch up" if it temporarily loses and then regains a satellite signal. So don't believe it if it says (for example) that your Pendolino is travelling at 145 mph. But, in areas of good satellite signals, GPS can be pretty accurate.

 

[Minilad]

The Railway Performance Timing Guide discusses use of GPS to measure speeds. See pages 14 to 16 of the free pdf. file download available at:

http://www.railperf.org.uk/index/timing-guide

Note that satellite reception is usually poor on Voyager type trains, and less than ideal on Pendolinos. Don't rely on 100% accuracy everywhere. You lose reception in tunnels, and sometimes where there are lots of trees - the GPS can try to "catch up" if it temporarily loses and then regains a satellite signal. So don't believe it if it says (for example) that your Pendolino is travelling at 145 mph. But, in areas of good satellite signals, GPS can be pretty accurate.

I have just joined this organisation. They do seem to offer good advice

 

[Peter Mugridge]

For a good price and far more accurate than anything I've used on my iphone, is this:
http://www.holux-uk.co.uk/holux-gpsport-245.php?it=173&gclid=CP_t1vn3s60CFYEmtAodEnarWA

It also data logs the journey and you can plot speed vs distance, or speed vs time graphs and also plot the route on google earth. It can take a few moments to lock to a signal, but once it's got it, it holds on fine.

A quick video I took of it working once:
http://www.youtube.com/watch?v=yDLme4eGE5A

This is the same as the one I currently use; it is extremely sensitive and is designed to work off reflected as well as direct signals.
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Not all GPS devices though take elevation into account when calculating speed so if this is the case and you are not dead level then the speed displayed won't be your true speed.

It is also programmed for gradients - it records your height above sea level and the change in elevation from your starting point.

 

[daikilo]

I have just joined this organisation. They do seem to offer good advice

In theory, all Satnav units take spot points from satelites and then calculate requested data based on those recordings. This means that the speed between any two recorded points will be calculated assuming a straightline routing. Frequency of position referencing will be key.

This is likely to lead to insignificant errors for a recent Satnav unit measuring a train travelling at say 125mph every say 1 second but could be significant for older units with a lower refresh rate.

I have read above that some are suggested to jump to adjacent roads but I doubt this actually happens, unless programed to do so.

I have however monitored GPS speed v. car display on a mixed straight and curved road route and can confirm that whilst on straight road the indicated car speed and GPS speed are close and the delta constant, the GPS speed declines through curved sections when the car speed is frozen at a constant speed by the speed control function. The same will apply to a train.

 

[Zoe]

It is also programmed for gradients - it records your height above sea level and the change in elevation from your starting point.

But does it actually use this information to calculate your speed? Easiest way to find out for sure would be to take it into an elevator and see if you get a speed other than zero.

 

[OxtedL]

But does it actually use this information to calculate your speed? Easiest way to find out for sure would be to take it into an elevator and see if you get a speed other than zero.

Or throw it off a building.

 

[Zoe]

Or throw it off a building.

(Doesn't work now you've got rid of the elevator bit...)

I've put the elevator bit back. No idea if you'd actually be able to get a signal from inside an elevator though.

 

[daikilo]

But does it actually use this information to calculate your speed? Easiest way to find out for sure would be to take it into an elevator and see if you get a speed other than zero.

You will only get a zero speed if the satelites are overhead. As the position is taken by triangulation between at least 3-5 satelites this test will not work. You should always get a delta value (speed).

 

[VideozVideoz]

Note that satellite reception is usually poor on Voyager type trains, and less than ideal on Pendolinos.

I've tried using my iphone gps on a Pendolino and it hardly ever knows where I am even though i'm sat near a window. Must be to do with the wires within the window which is why you cant get a good mobile signal (unless there's enhanced coverage of course!). With the iphone if it cant get a gps signal, it shows the location of the mast you're currently locked onto.

 

[daikilo]

I've tried using my iphone gps on a Pendolino and it hardly ever knows where I am even though i'm sat near a window. Must be to do with the wires within the window which is why you cant get a good mobile signal (unless there's enhanced coverage of course!). With the iphone if it cant get a gps signal, it shows the location of the mast you're currently locked onto.

I am told that certain coaches/units such as most Virgin are effectively masked to GPS signals through bodywork and window coatings. Your explanation may be correct but is illogical.

 

[VideozVideoz]

I am told that certain coaches/units such as most Virgin are effectively masked to GPS signals through bodywork and window coatings. Your explanation may be correct but is illogical.

Well, I was told this story by a train manager on the train itself... no other reference points other than that

 

[Zoe]

You will only get a zero speed if the satelites are overhead. As the position is taken by triangulation between at least 3-5 satelites this test will not work. You should always get a delta value (speed).

As far as I know GPS doesn't tell you speed but only your position. If you are in an elevator your horizontal position would not have changed so there will be no horizontal distance moved and your horizontal speed will be zero. If you are not moving at all your speed is zero as your position has not changed so if your unit does not take into account change an elevation when calculating speed, why would it show anything other than your horizontal speed?

 

[Sox]

Thanks for all the responses, my original query generated quite a bit of interest.

As a bit of a gadgophile, I have decided to buy a Holux GPS 245 (£49 off e-bay but I think it will be on a slow boat from China).

 

[Peter Mugridge]

The Holux 245 does get a signal in a 390, no problem.

It will also get a signal in a Voyager, but only in the vestibules, not the cabin. That's the only place it won't receive on any train in the UK!

 

[AeroSpace]

GPS is generally fairly accurate until you go round a curve, and the GPS takes the chord of the curve - giving an artificially high reading

Surely it will give an artificially low reading? And in any case, the error will be a fraction of a percent.

 

[Mike C]

I think all the debate about accuracy based on taking chord lengths or versines and changes in altitiude is a bit pedantic when we're talking about railway measurements. Trains don't change direction or altitude quickly - in fact, I can't think of much that does so slower. Oil tankers maybe.

In terms of accuracy - there will be a theoretical error (as there is with anything), but for the purposes of seeing how fast a train or car is travelling, and provided the user is aware of the limitations of GPS speed measurements (spikes when going under bridges etc...), I can't see a problem.

Going back to the specific unit the OP has purchased, the Holux GP245 is incredibly sensitive. I've had mine logging without my knowledge from inside my pocket and when I downloaded it later, it had perfectly traced my route not only where I'd walked but the last 5 minutes of the train journey from where it was presumably activated. That was through the train window AND in my pocket.

 

[Eagle]

As a bit of a gadgophile, I have decided to buy a Holux GPS 245 (£49 off e-bay but I think it will be on a slow boat from China).

I'm assuming you don't have a smartphone then, as there are loads of free GPS tachymeter apps available on the market. I use Android Compass (which is good enough to correct for non-horizontal travel, not that railways are particularly slopy anyway... :roll.

Then again your new GPS device is probably more accurate and has better signal than a phone.