Differential GPS on the n810?
 

The LD-3W bluetooth GPS is listed under accessories for the N810.

Is this a mistake, or could you really have two GPS devices available?

It's a shame the range of bluetooth is so limited. Differential GPS is very accurate if the data is processed properly. With two GPSs, the n810 could be an electronic tape measure or a device to help you find your car in a car park. How much of a killer app would that be?

Re: Differential GPS on the n810?
 

Ooo, nice idea, dormant! I don't have an answer but it *looks* possible...

Re: Differential GPS on the n810?
 

I'm not sure I follow.. Differential GPS isn't two GPS receivers, it's a concept of one GPS receiver plus a correction factor sent (by radio, for example) from a fixed-point location which _also_ has a GPS receiver and can (because it's in a fixed, well-known location) calculate an adjustment factor that can be transmitted to you.

Re: Differential GPS on the n810?
 

Nokia is not an original manufacturer of GPS units as only manufacturers of GPS chips can be considered as original manufacturers of GPS units.
So a range of GPS devices available for use with Nokia 770/800/810 is in no way limited.
Any bluetooth GPS unit can be applied.
Don't expect Nokia to offer full range of GPS units.
Nokia stays for cell phones not GPS units or GPS technology.

Neverthless I have developed algorithm and posted request to Nokia maemo developers to introduce two GPSs operation in N810 and in other models to have better quality GPS data and better GPS signal received for processing to avoid and limit signal lost or no GPS fix problem.

If you are a developer and can write a code I can provide you with more details on how to implement that feature called 2 GPSs navigation operation.

Darius

Re: Differential GPS on the n810?
 

Bum, I thought I'd deleted this thread, not posted it.

TA-t3: There are two different types of differential GPS. Most people recognise the type you mention. But you can buy commercial surveying equipment that achieves much greater accuracy by using two or more GPS receivers and processing the data from them together - either in real time over a radio link to a computer or in post-processing. Accuracy can be less than a centimetre (I am a volcanologist and we use this type of GPS data to measure deformation of volcanoes.)

"Proper" differential GPS won't work on something like the N810. Commercial units use the L2 frequency (no, I don't know what it is either) and information that isn't available in NMEA sentences.

So I think all could be done is just differencing the two GPS measurements. I haven't tested this, but it might give accuracy of about 1m under the right conditions. Good enough to find a car, but you'd have to be within 10m for the bluetooth to work anyway.

Another idea for greatness dead in the water.

Darius2006, I am not a coder. I can script, but the last programming I did was in FORTRAN, in the days when it was in capital letters. The n800 might just get me back into coding - I am tempted to do something based on gps-saver.

Re: Differential GPS on the n810?
 

Oh yeah then it could be used on missiles!
Great idea!
:)

Re: Differential GPS on the n810?
 

What are you talking about?

Re: Differential GPS on the n810?
 

GPS has been used in cruise missiles since the mid 90s. Bombs really don't need any great accuracy.

For anyone reading this thread out of interest, I should clarify that the type of differential GPS I was talking about has a relative accuracy of less than a centimetre. The absolute accuracy is much larger, and depends on how long you record data for and how it is processed, but is probably a few metres.

So you can tell how far apart two things are, and the direction between them, with much greater accuracy than the actual position of either of them.

Re: Differential GPS on the n810?
 

Awesome app! This really doesn't need 2 GPS receivers unless your car moves while it's at the car park. :D :D Simply record the location of the car as you leave it, then display it on a satellite image of the car park. Add your current location and you shouldn't "loose" your car ever again!

Re: Differential GPS on the n810?
 

Admittedly, I don't have the very best of GPS receivers, but if I take it off the top of the dash next to the windshield and place it where my N800 rests against the face of my speedometer (don't worry, it only blocks < 25 mph and > 80 mph), I can't get a GPS fix. If the N810 doesn't have an external GPS antenna, is it going to be useful? Do other GPS units (i.e. Garman, etc) have external antennas?

Re: Differential GPS on the n810?
 

Not sure it will work in the specific position you mentioned, but Thoughtfix has tried the N810's GPS when mounted with the car-mounting kit, and it does work.

Re: Differential GPS on the n810?
 

a) Transflective screen will help in-car usage too.
b) You really don't want to be leaving a bluetooth device in the car. For that matter, a GPS mount is an inviting sign for thieves. Something they can see on a BT scanner tells them there's something valuable and portable inside.
c) Hey, using an external BT GPS + N810 sounds cool, but you have range issues. If you use two n810s (or n800s with BT GPS) and an ad hoc connection, you'd get more range, wouldn't you?

Re: Differential GPS on the n810?
 

Sure would be. But it's getting very costly.

As for storing you location when you park your car, yes that'd work and it'd be nice to have a simple app that stores a location then later gives you a direction and distance to it.

But people never plan to lose their cars and are going to get bored of manually storing the location every time they park. You need something that is a no-brainer. I think there's a new Garmin unit (Nuvi 700?) that provides just this service - it automatically stores the location when you remove it from the car mount.

Can the range of bluetooth be extended using this method?

Re: Differential GPS on the n810?
 

If you only can find me a maemo coder I can provide you with the same feature at Nokia tablet for free.

Darius

Re: Differential GPS on the n810?
 

Differential GPS in both senses is precisely the same thing; the only difference is how the results are represented. In either case, the GPS reading is taken at two places at practically the same time. The difference is computed. In the "normal" case, the result is then added to the precisely known location of one point. For the situation with both endpoints unknown, the only data that can be given is the difference.

In both cases, however, the measurements must be taken together. The drift in the signal will cause a progressive loss in accuracy the longer you are in the store, so you might only find your car to the same level of accuracy you can get in general, after a few hours. Still, at least for car-finding, that's probably close enough.
And presumably, if you have some BT gadget you leave in the car (maybe a handsfree), you can recognise the disconnect when you walk away, and automatically save a position there. A daemon to do this would be nice, and I'd probably write one if I had an N810. (anyone want to buy me one? please? I was afraid of that :-)

Re: Differential GPS on the n810?
 

Yeah, another thing about BT GPS Transceivers: they auto shutoff after 5 minutes. But, well, that'd be good enough too, right. When the BT signal on the GPS transceiver goes out, log the position.

Other problems with finding cars are that they're often parked in garages.

Many cars are getting BT installed for various things. If you're going to write the BT disconnect demon, may I suggest the following options as well:

a) record the position on a significant and unreversed degradation of the signal (rssi or lq?) as when someone gets out of a car.
b) events for when a known BT MAC comes into range. This would be very useful when wired to the MAC of the Boss's cellphone. Make a desktop widget too and call it "KittyBell". It woudl probably help you find your car too.

Re: Differential GPS on the n810?
 

This could be interesting:

http://artico.lma.fi.upm.es/numerico...nio/pd/pd.html

is for etrex gps, but could it be usefull?
It uses RINEX files to compare and do diferential postprocess gps