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Anonymous
How Quick GPS Works
Oct 21 2007, 12:48 AM EDT | Post edited: Oct 21 2007, 12:48 AM EDT
Some other posts on the Wiki reference Quick GPS, but seem to mistake what it does, so I thought I'd clear it up, being a professional in the space.

Quick GPS does not "triangulate" using cellular networks, not even close. Let me start by telling you how a GPS gets a fix on its location, and then explain how Quick GPS offers a shortcut.

The GPS chip receives a synchronized timed signal from the satellites (birds) the US DoD launched into orbit. Each bird uses a different channel. With a good signal from three or more birds, GPS starts to get a fix. It does this by calculating the time difference between the reception of the different signals, then calculating the relative distances to each of the birds, then figuring out where it sits in the middle of the birds.

The GPS calculates four spheres, and its located somewhere on the surface of each of these spheres. There is only one point where these four spheres intersect. That's you.

If you're good at geometry, you might think that it needs 4 birds to get a fix, but in fact, if the GPS assumes that you are on earth, that provides another sphere, so it only requires 3 birds to get a decent fix. More adds altitude and accuracy.

But the GPS needs to know where each of the birds is before it can decide where IT is. That information is not calculated, but is available in a detailed download of orbital data provided by the DoD called ephemeris data. It is transmitted...from the bird to your GPS. For a cold start, your GPS needs to download the entire file, without interruptions in the signal - BEFORE it can even start getting a fix. In fact, the GPS may not even know which channels to tune into, since it doesn't yet know which birds are currently overhead. This causes a slow first fix.

Quick GPS, is simple. Ephemeris data is passed thru WiFi or cellular data connection ahead of time, and you never have to wait for it to download over the satellite. Awesome.
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Anonymous
1. RE: How Quick GPS Works
Oct 27 2007, 6:10 AM EDT | Post edited: Oct 27 2007, 6:10 AM EDT
Nice article, but I think the problem for most people (including myself) is that QuickGPS simply does not work. TTFF is the same no matter if the downloaded data are valid or expired or not existing at all. (I have FujitsuSiemens Pocket Loox N560 with the official update that includes HTC QuickGPS) Nobody really knows what to expect and how to be sure that it works or does not work. It is not easy to measure TTFF reliably.
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Anonymous
2. RE: How Quick GPS Works
Oct 30 2007, 10:09 AM EDT | Post edited: Oct 30 2007, 10:09 AM EDT
This superficial description begs so many questions! For instance if you get good signals for long enough to download an ephemeris from the satellites, QuickGPS data is now probably out of date. So does it get delivered to GPS nevertheless? Certainly QuickGPS does not update its validity duration to suggest that a web update is not so crucial!

More basically, does QuickGPS have to be "running" to update the GPS at every start-up, or is it an invisible service?
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sliders7
sliders7
3. RE: How Quick GPS Works
May 3 2008, 10:21 PM EDT | Post edited: May 3 2008, 10:21 PM EDT
"Some other posts on the Wiki reference Quick GPS, but seem to mistake what it does, so I thought I'd clear it up, being a professional in the space.

Quick GPS does not "triangulate" using cellular networks, not even close. Let me start by telling you how a GPS gets a fix on its location, and then explain how Quick GPS offers a shortcut.

The GPS chip receives a synchronized timed signal from the satellites (birds) the US DoD launched into orbit. Each bird uses a different channel. With a good signal from three or more birds, GPS starts to get a fix. It does this by calculating the time difference between the reception of the different signals, then calculating the relative distances to each of the birds, then figuring out where it sits in the middle of the birds.

The GPS calculates four spheres, and its located somewhere on the surface of each of these spheres. There is only one point where these four spheres intersect. That's you.

If you're good at geometry, you might think that it needs 4 birds to get a fix, but in fact, if the GPS assumes that you are on earth, that provides another sphere, so it only requires 3 birds to get a decent fix. More adds altitude and accuracy.

But the GPS needs to know where each of the birds is before it can decide where IT is. That information is not calculated, but is available in a detailed download of orbital data provided by the DoD called ephemeris data. It is transmitted...from the bird to your GPS. For a cold start, your GPS needs to download the entire file, without interruptions in the signal - BEFORE it can even start getting a fix. In fact, the GPS may not even know which channels to tune into, since it doesn't yet know which birds are currently overhead. This causes a slow first fix.

Quick GPS, is simple. Ephemeris data is passed thru WiFi or cellular data connection ahead of time, and you never have to wait for it to download over the satellite. Awesome."
Wonderful Explanation, now i have better understanding towards "Quick GPS"

but I'm still confused and need answer to this questions:
1. If Quick GPS software download Ephemeris data and give it to GPS module, where the data located and how GPS module read it to help acquired faster fix?

2. if Kaiser able to read Ephemeris data downloaded by Quick GPS Software, what if TILT connect to The External Bluetooth GPS Module? does it help at all? because the Hardware is separated. again..does it help at all?

3. iF Kaiser connected to The External Bluetooth GPS Module, why it got Fix fast? is that mean Built in GPS most Kaiser are weak? compare to the Portable external bluetooth GPS?

4. This questions give me headache all the time:
is a chip called SiRF Star III found inside PDA do the actual physical chip? small? Tiny chips? compare with the one found on Portable External Bluetooth GPS module? the fact they both using the same SiRF Star III chip.
- is the chips are the same, why Portable External Bluetooth GPS module get Fast Fix? and the one inside PDA don't?
- if not the same, is that mean GPS chip on most PDA with built in GPS (ex: kaiser, Artemis) are Weak? or budget version?

Any explanation will be greatly appreciated.
Thank You!
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Rainman76
Rainman76
4. RE: How Quick GPS Works
May 3 2008, 11:15 PM EDT | Post edited: May 3 2008, 11:15 PM EDT
"Wonderful Explanation, now i have better understanding towards "Quick GPS"

but I'm still confused and need answer to this questions:
1. If Quick GPS software download Ephemeris data and give it to GPS module, where the data located and how GPS module read it to help acquired faster fix?

2. if Kaiser able to read Ephemeris data downloaded by Quick GPS Software, what if TILT connect to The External Bluetooth GPS Module? does it help at all? because the Hardware is separated. again..does it help at all?

3. iF Kaiser connected to The External Bluetooth GPS Module, why it got Fix fast? is that mean Built in GPS most Kaiser are weak? compare to the Portable external bluetooth GPS?

4. This questions give me headache all the time:
is a chip called SiRF Star III found inside PDA do the actual physical chip? small? Tiny chips? compare with the one found on Portable External Bluetooth GPS module? the fact they both using the same SiRF Star III chip.
- is the chips are the same, why Portable External Bluetooth GPS module get Fast Fix? and the one inside PDA don't?
- if not the same, is that mean GPS chip on most PDA with built in GPS (ex: kaiser, Artemis) are Weak? or budget version?

Any explanation will be greatly appreciated.
Thank You!"
1. The data is stored on the device itself. It's not just the GPS itself that needs help acquiring quickly, but the applications that utilize GPS hardware.

2. It may help.. I'm not sure as I have never connected an external GPS unit to my Tilt. I see no reason to.

3. No, the GPS is not weak, it's just meant to help it acquire the signal faster. All GPS devices will take a while to acquire a fix if they haven't been connected for a while. Again, don't forget, the GPS satellites in space orbit the earth faster than the earth's actual rotation.

4. SiRF Star III is just a different chipset. It does have a reputation of acquiring GPS fixes faster than older NMEA0183 chipsets, which is what is in the Tilt, Artemis, etc.
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sliders7
sliders7
5. RE: How Quick GPS Works
May 4 2008, 12:06 AM EDT | Post edited: May 4 2008, 12:06 AM EDT
"1. The data is stored on the device itself. It's not just the GPS itself that needs help acquiring quickly, but the applications that utilize GPS hardware.

2. It may help.. I'm not sure as I have never connected an external GPS unit to my Tilt. I see no reason to.

3. No, the GPS is not weak, it's just meant to help it acquire the signal faster. All GPS devices will take a while to acquire a fix if they haven't been connected for a while. Again, don't forget, the GPS satellites in space orbit the earth faster than the earth's actual rotation.

4. SiRF Star III is just a different chipset. It does have a reputation of acquiring GPS fixes faster than older NMEA0183 chipsets, which is what is in the Tilt, Artemis, etc. "
wow... Thank You so much!!

I'm very satisfied, Good Knowledge!
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d-signet

d-signet
6. RE: How Quick GPS Works
Jun 10 2008, 7:40 AM EDT | Post edited: Jun 10 2008, 7:40 AM EDT
i think the problem here is that knowing where the birds are is irrelevant unless the system makes certain assumptions.

ie....where YOU are. Not precise co-ordinates obviously, but it at least needs to guess which continent you are on before this information would be useful.

its fine knowing that there are three birds over spain....but that doesn't help if it doesnt know that you are actually in the UK. it still needs to have a look and see which birds it can actually SEE before it can work out where you are, making the whole system irrelevant unless you live in the locale that quickGPS assumes you are in.

is this why some people report the system as being useless while others swear by it?

as the OP said..." since it doesn't yet know which birds are currently overhead. This causes a slow first fix." . Even with the lates updates, it still CANT know which ones are overhead without guessing roughly where it is, before then trying to get a fix.
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Anonymous
7. RE: How Quick GPS Works
Jun 22 2008, 3:45 AM EDT | Post edited: Jun 22 2008, 3:45 AM EDT
How will be the best way to display the gps on the new Diamont phone I am really struggling to make it work
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Anonymous
8. RE: How Quick GPS Works
Jul 3 2008, 6:14 AM EDT | Post edited: Jul 3 2008, 6:14 AM EDT
"If you're good at geometry, you might think that it needs 4 birds to get a fix, "
is'nt it "3 birds" rather than 4?

two spheres intersect in a line, and third one makes it a point?
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Anonymous
9. RE: How Quick GPS Works
Jul 3 2008, 7:06 AM EDT | Post edited: Jul 3 2008, 7:06 AM EDT
i THINK....

2 spheres will intersect more than once (think of a venn dagram, there is an intersection at both sides of the union set - spheres are worse)

3 spheres will give you a single set point, but only a in 2 dimensions

a 4th will give you the altitude fix too.
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Anonymous
10. RE: How Quick GPS Works
Aug 28 2008, 6:02 PM EDT | Post edited: Aug 28 2008, 6:02 PM EDT
I have a slightly different problem... I have a brand new HTC P6500 Sedna that has quick GPS pre-loaded

the manual has two pages saying effectively stand outside download an ephemeris and away you go....

OK fair enough I stood outside and downloaded an ephemeris.....but nothing happens no maps nothing apart from the data being good for six days. Am I being dense or is the mapping software a different product?

If I do need extra software ...what is it called?

I am not to bothered about car use ..more of a pedestrian

contact me on [email protected] if you can help
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Anonymous
11. RE: How Quick GPS Works
Sep 3 2008, 8:04 PM EDT | Post edited: Sep 3 2008, 8:04 PM EDT
2 spheres provide a union equivalent to a oval of sorts. Consider 2 balls that overlap. GPS receivers know they are a certain distance from a GPS (based on time differences and other fancy physics), making them ON the SURFACE of a sphere centered on the satellite. With 2 satellites, you have 2 spheres centered over different areas. Think of 2 overlapping balls to help clarify it. If you have 2 overlapping spheres, and you know you're on the SURFACE of those spheres, then there will be an oval shape at the point where the surfaces of both spheres intersect.

With 3 spheres, you get 2 set points. Which means a position lock with 3 satellites is ONLY possible if at least 1 variable is known. Generally speaking, that variable is normally height above sea level (aircraft have an alitmeter, a device which measures just that and with the right equipment can be fed into the GPS receiver). In this case, 1 point will be somewhere near that altitude above sea level, the other won't be, which leaves us with only 1 point.

If altitude is not known, some other peice of data needs to be known and a little luck is required. For example, if you're receivers know what continent you're on (roughly) and only 1 of 2 points is near there, it can "assume" an throw away the other point. But that can be dangerous since you might have moved continents and it could be incorrect.

Once you have a 4th satellite, you're down to 1 point. 1 single location in all of space. Which is why you now know altitude as well. Additional satellites allow this position to be tweaked. Think of it as if with 4 satellites the points are the size of your living room (margin of error in times, etc). With more and more satellites, the points get smaller and smaller, to the size of your glass, and eventually the size of the quarter in your pocket. If, of course, there were enough satellites to make the points that small.
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Anonymous
12. RE: How Quick GPS Works
Sep 5 2008, 12:53 PM EDT | Post edited: Sep 5 2008, 12:53 PM EDT
"1. The data is stored on the device itself. It's not just the GPS itself that needs help acquiring quickly, but the applications that utilize GPS hardware.

2. It may help.. I'm not sure as I have never connected an external GPS unit to my Tilt. I see no reason to.

3. No, the GPS is not weak, it's just meant to help it acquire the signal faster. All GPS devices will take a while to acquire a fix if they haven't been connected for a while. Again, don't forget, the GPS satellites in space orbit the earth faster than the earth's actual rotation.

4. SiRF Star III is just a different chipset. It does have a reputation of acquiring GPS fixes faster than older NMEA0183 chipsets, which is what is in the Tilt, Artemis, etc. "
1. Applications do not use this data. It would not be of any benefit.

2. It will not help. That would be two different GPS units. Each would need its own copy of the data.

3. Yes it is weak. It is the slowest aquiring unit that I have used since the Rockwell Trooper in 1993.

4. NMEA0183 is specification of messages that are output by various devices. The Tilt and other names devices use the Qualcomm chip. This is the cause of the slow aquisition.

I also own a HTC x7501. This device uses the Sirf III chipset. It is much better at aquistion times. I have many GPS devices from cheap bluetooth units up to RTK units. Most have there own littlie quirks, but this Qualcomm takes the prize for slowness to aquisation.

In the fifteen years that I have programmed GPS based software, this unit is the slowest. However, once locked on, it does a fair job at positioning. Would not depend on it for the type of work that my users do.
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Anonymous
13. RE: How Quick GPS Works
Sep 24 2008, 9:00 PM EDT | Post edited: Sep 24 2008, 9:00 PM EDT
"2 spheres provide a union equivalent to a oval of sorts. Consider 2 balls that overlap. GPS receivers know they are a certain distance from a GPS (based on time differences and other fancy physics), making them ON the SURFACE of a sphere centered on the satellite. With 2 satellites, you have 2 spheres centered over different areas. Think of 2 overlapping balls to help clarify it. If you have 2 overlapping spheres, and you know you're on the SURFACE of those spheres, then there will be an oval shape at the point where the surfaces of both spheres intersect.

With 3 spheres, you get 2 set points. Which means a position lock with 3 satellites is ONLY possible if at least 1 variable is known. Generally speaking, that variable is normally height above sea level (aircraft have an alitmeter, a device which measures just that and with the right equipment can be fed into the GPS receiver). In this case, 1 point will be somewhere near that altitude above sea level, the other won't be, which leaves us with only 1 point.

If altitude is not known, some other peice of data needs to be known and a little luck is required. For example, if you're receivers know what continent you're on (roughly) and only 1 of 2 points is near there, it can "assume" an throw away the other point. But that can be dangerous since you might have moved continents and it could be incorrect.

Once you have a 4th satellite, you're down to 1 point. 1 single location in all of space. Which is why you now know altitude as well. Additional satellites allow this position to be tweaked. Think of it as if with 4 satellites the points are the size of your living room (margin of error in times, etc). With more and more satellites, the points get smaller and smaller, to the size of your glass, and eventually the size of the quarter in your pocket. If, of course, there were enough satellites to make the points that small."
Actually, the 4th satellite is needed to calculate the clock offset between the gps receiver and "gps time". the "system" knows what time the signal was sent from the satellite but it needs to know that in relation to the time in the receiver. this needs to be very accurate.

so, there are 4 variables to solve - X, Y, Z, time offset, therefore you need 4 satellites so that you can make 4 equations to solve for the 4 unknowns.

after that, it's just a matter of redundancy in your least squares solution - the more satellites you have, the better your solution.

that's the simple explanation.
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Anonymous
14. RE: How Quick GPS Works
Sep 28 2008, 7:53 AM EDT | Post edited: Sep 28 2008, 7:53 AM EDT
"I have a slightly different problem... I have a brand new HTC P6500 Sedna that has quick GPS pre-loaded

the manual has two pages saying effectively stand outside download an ephemeris and away you go....

OK fair enough I stood outside and downloaded an ephemeris.....but nothing happens no maps nothing apart from the data being good for six days. Am I being dense or is the mapping software a different product?

If I do need extra software ...what is it called?

I am not to bothered about car use ..more of a pedestrian

contact me on [email protected] if you can help"
Hey,

I have the exact same problem in my HTC Touch Pro, have you had some solutions yet, if possible, please help me out. My email is [email protected]

Thank you
Manfred
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Sgarrela

Sgarrela
15. RE: How Quick GPS Works
Oct 2 2008, 2:47 PM EDT | Post edited: Oct 2 2008, 2:47 PM EDT
I worked on the team that designed the original NavSat system for DoD. This was the predicessor to GPS. In those days, we determined the position on the ground using the doppler shift of a 5 MgHz tone that the bird emitted, rather than the syncronized time signal that GPS uses. Even then, the ephemeral data was the key. We tested the first backpack style NavSat systems in 1969. They weighed 38 pounds, cost $1 Million each, and weren't nearly as accurate as the GPS in my Tilt today. What a difference 40 years makes. Thanks for clarifying the system operation for all.
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Sgarrela

Sgarrela
16. RE: How Quick GPS Works
Oct 2 2008, 3:14 PM EDT | Post edited: Oct 2 2008, 3:14 PM EDT
You will need some kind of mapping software. Google Maps can be downloaded for free, but you will need a data plan, since Google maps will access the map detail from an internet connection. This can get expensive if you don't have an unlimited data plan. You can also purchase and download maps along with a GPS program that will give you turn by turn directions while driving or walking. I am using a system by Pharos/Ostia on my AT&T Tilt (HTC 9125) and it works great. (www.pharos.com) I keep my Quick GPS data up to date, so the system can boot up quickly.
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Sgarrela

Sgarrela
17. RE: How Quick GPS Works
Oct 2 2008, 3:19 PM EDT | Post edited: Oct 2 2008, 3:19 PM EDT
Quck Correction on the Pharos website. It is www.pharosgps.com.
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Anonymous
18. RE: How Quick GPS Works
Dec 28 2008, 10:55 AM EST | Post edited: Dec 28 2008, 10:55 AM EST
I have a new HTC phone. It has QuickGPS but I dont know how to use it......Can you explain me how to use the QuickGPS Software on the mobile phone....It has a small hole on the backside of the phone. Can you mail me at [email protected]
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denco7
denco7
19. RE: How Quick GPS Works
Dec 28 2008, 12:10 PM EST | Post edited: Dec 28 2008, 12:10 PM EST
"I have a new HTC phone. It has QuickGPS but I dont know how to use it......Can you explain me how to use the QuickGPS Software on the mobile phone....It has a small hole on the backside of the phone. Can you mail me at [email protected]"
Did you bother to read the thread at all ? Quick GPS is not GPS software. It is just a program to pre- perform the preliminaries of getting a GPS fix.
To use GPS you still need GPS software. Please read the thread and then do a search on GPS software.
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