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Lord Raiden's Avatar
Lord Raiden is offline Lord Raiden
2009-09-16 , 20:44
Posts: 1,562 | Thanked: 349 times | Joined on Jun 2008
#1
Ok, I've been doing some research into this, and aside from having a better GPS chip, one of the things that the stand along GPS units, such as the Garmins, have that makes them better than the NIT for GPS locking, and allows them to lock on in only a matter of a few seconds is a rather neat system that I've unofficially called "GPS drift adjustment". Essentially what the GPS's do is, when they do their first time lock, it can take 2-10 minutes or more to get a full lock. After that it's just a few mere seconds.

The way they achieve this is to remember the last known coordinates of the GPS satellites they had locked onto when they're turned off, and then when they are powered on and go for their initial lock again, they take that information, adjust for date/time and figure out what the drift is. Then they apply that information and use it to look for the satellites they need, and surprisingly enough, they're accurate about 99% of the time.

So for example, if GPS satellite 5 was last seen at 12x65 degrees (12 degrees on the compass, and 65 degrees vertical assent) and it drifts 8x12 degrees every hour, then the GPS device simply needs to do is take that information, look at the last known position, the current time, and then calculate where it should be now. By rights it should then find the satellite right where it expects it to be. I think that if we could apply something like this to the GPS on the NIT, either directly, through a secondary app, or via any of the associated GPS apps (Maemo Mapper, Navit, etc) then GPS locks could be done really, really darned quickly. Heck, in a matter of a few seconds from power on just like the big boys do. Whatcha guys think? Anyone wanna try and tackle this?
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Last edited by Lord Raiden; 2009-09-16 at 20:47.
 
Thesandlord is offline Thesandlord
2009-09-16 , 20:51
Posts: 1,213 | Thanked: 356 times | Joined on Jan 2008 @ California and Virginia
#2
is not exactly that which a-gps tries to do?
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shadowjk is offline shadowjk
2009-09-16 , 20:57
Posts: 1,258 | Thanked: 672 times | Joined on Mar 2009
#3
The gps is essentially one big black box. We do not know the protocol that the gps chip speaks, we do not know the capabilities of the gps chip, and we don't know how to modify the existing A-GPS system. It would require reverse engineering all of gpsdriver and the related supld programs. This is a very large task for what's at best only marginal improvement.

The driver might already be caching data. Anecdotally erasing the files written by the gps driver has improved getting a fix for some people... Myself I've seen gpsdriver die/crash without the rest of the system caring/noticing, in which case I'd never gotten a fix because nothing was even trying to.

I usually get a fix in 20-30 seconds after a week of no use, and faster lock if I switch off gps for a few minutes and then try again. I always have agps enabled.
Last edited by shadowjk; 2009-09-16 at 21:01.
 
Den in USA's Avatar
Den in USA is offline Den in USA
2009-09-16 , 21:00
Posts: 1,390 | Thanked: 642 times | Joined on Nov 2007 @ California USA
#4
Originally Posted by Lord Raiden View Post
Ok, I've been doing some research into this, and aside from having a better GPS chip, one of the things that the stand along GPS units, such as the Garmins, have that makes them better than the NIT for GPS locking, and allows them to lock on in only a matter of a few seconds is a rather neat system that I've unofficially called "GPS drift adjustment". Essentially what the GPS's do is, when they do their first time lock, it can take 2-10 minutes or more to get a full lock. After that it's just a few mere seconds.
True, my Garmin Nuvi 660 gets a "lock" within 30 seconds or so. However, I get a "lock" within 40 seconds using my N800 with a bluetooth GPS. I don't think that GPS uses "drift adjustment".
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ioioio is offline ioioio
2009-09-16 , 23:12
Posts: 86 | Thanked: 55 times | Joined on May 2009
#5
Raiden, do you know if what you are saying is controllable on the software side? I would think that all locks would be done on the hardware side transparent from any apps & drivers. Do we know the GPS chip make/model, if so we can just look up the datasheet and see whats what.
 
shadowjk is offline shadowjk
2009-09-16 , 23:55
Posts: 1,258 | Thanked: 672 times | Joined on Mar 2009
#6
It's a TI module... TI530 maybe, my memory isn't working tonight. The datasheet can be summarized into "It's a GPS chip. You can put it in portable devices and stuff."
 
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Lord Raiden is offline Lord Raiden
2009-09-17 , 01:16
Posts: 1,562 | Thanked: 349 times | Joined on Jun 2008
#7
A-GPS works fine for those who can use it. I don't have a bluetooth enabled phone, so I can't benefit from a-gps. I have to go through the old fashioned 2-5 minute lock cycle every time. Then again, I'm up near the 45th parallel, so GPS for us blows chunks anyways, unless you've got a Garmin. You really have to be below the 50th parallel before you start getting decently quick GPS locks. Or at least that's what I've been seeing. And to top that off, the best signal strength I've seen from any satellites has been about 50% around here, even on clear days out in the open under an open sky.
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ioioio is offline ioioio
2009-09-17 , 01:30
Posts: 86 | Thanked: 55 times | Joined on May 2009
#8
Originally Posted by shadowjk View Post
It's a TI module... TI530 maybe, my memory isn't working tonight. The datasheet can be summarized into "It's a GPS chip. You can put it in portable devices and stuff."
Little Google searching on ti530 found that the n810 has the Texas Instruments Navilink 4.0 TI GPS5300 chipset. It's OEM only, so no datasheet for me. Can't find any info, lock times, etc for the chip. Just the following;

http://focus.ti.com/general/docs/wtb...emplateId=6123

And as someone else said, supposedly A-GPS does this;

http://betalabs.nokia.com/blog/2008/...beta-for-n810/

Reading further

http://www.wmexperts.com/articles/gp..._tutorial.html

on a cellphone, the assistance for the GPS would come from the base station.
 
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verumgero is offline verumgero
2009-09-17 , 02:15
Posts: 221 | Thanked: 43 times | Joined on Oct 2007 @ Sendai, Japan
#9
Originally Posted by Lord Raiden View Post
Ok, I've been doing some research into this, and aside from having a better GPS chip, one of the things that the stand along GPS units, such as the Garmins, have that makes them better than the NIT for GPS locking, and allows them to lock on in only a matter of a few seconds is a rather neat system that I've unofficially called "GPS drift adjustment". Essentially what the GPS's do is, when they do their first time lock, it can take 2-10 minutes or more to get a full lock. After that it's just a few mere seconds.

The way they achieve this is to remember the last known coordinates of the GPS satellites they had locked onto when they're turned off, and then when they are powered on and go for their initial lock again, they take that information, adjust for date/time and figure out what the drift is. Then they apply that information and use it to look for the satellites they need, and surprisingly enough, they're accurate about 99% of the time.

So for example, if GPS satellite 5 was last seen at 12x65 degrees (12 degrees on the compass, and 65 degrees vertical assent) and it drifts 8x12 degrees every hour, then the GPS device simply needs to do is take that information, look at the last known position, the current time, and then calculate where it should be now. By rights it should then find the satellite right where it expects it to be. I think that if we could apply something like this to the GPS on the NIT, either directly, through a secondary app, or via any of the associated GPS apps (Maemo Mapper, Navit, etc) then GPS locks could be done really, really darned quickly. Heck, in a matter of a few seconds from power on just like the big boys do. Whatcha guys think? Anyone wanna try and tackle this?
HA! I knew it! I have a bluetooth GPS module for my n800 and I have noticed that it locks on real fast if I am close to the last place I was and it takes longer when I farther away. Best example would be from this last trip I took, I used GPS to find find a train station I had never been to and it locked on really fast. But, after about 9 hours on a train and a few hundred kilometers later I tried to get a lock and it took about 3 minutes.

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YoDude's Avatar
YoDude is offline YoDude
2009-09-17 , 02:25
Posts: 2,869 | Thanked: 1,784 times | Joined on Feb 2007 @ Po' Bo'. PA
#10
Can a small program be made that connects and then runs in the background?
 
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