(Posted in the other iOS location snafu thread since I was replying to specific posts there, but probably belongs here, as it's regarding info from this post today)
Overall, I was pretty pleased to see Apple's official response today. It took a little longer than I think many people would have liked, but it's generally plausible, and I still feel that Apple is generally one of the "good guys" in the realm of privacy. Minor issues pointed out here:
When they say that "Apple is not tracking the location of your phone", it may be true from a pedantic nature, but general location information about your phone was (and will continue to be if you opt to allow it) being passed along to Apple. It may not be highly accurate data, and it may have been purged or otherwise aggregated on their end to the point of not identifiable, but location data was passed on.
When they say "This data is sent to Apple in an anonymous and encrypted form. Apple cannot identify the source of this data.", I don't quite buy that. If they choose to take note of where the data came from, it could be identified, even if the identifying info is not explicitly in the data itself. Yes, this is a minor point, just throwing it out for sake of completeness.
Lastly, on this PR statement, I don't believe the two issues were really "bugs", but I could be convinced that they were simple oversights. Yes, there is a difference, although it's not really that important in the scope of explanation to the public.
But overall, these are small nits, and I applaud Apple for coming out and not only explaining what's going on, but taking steps to rectify the problems. To be honest though, they had little choice. The media and public at large were not going to let go of this easily.
Quote:
Originally Posted by melgross
They make it clear that it is anonymous. As we can see from Apple's statement today, this isn't what you insist it is.
As I alluded to above, any sizable amount of location-based data, even with no user-identifying bits, should not be assumed to be anonymous. It's possible that this particular data was not accurate enough to be identifiable, but I haven't seen anything (yet) that leads me to believe that's the case. Here is a great article, worth reading in its entirety:
The PARC article referenced within is also good, but more technical than most people will want to read.
Quote:
Originally Posted by melgross
Because of that, using this to track people is useless, and hasn't been allowed in court so far.
Key words: so far ! ;-)
Quote:
Originally Posted by Dickprinter
I, for one, always read the fine print so I can make educated choices.
Having said that, am I being naive?
PS: Thanks for not picking on me.
As for reading fine print, you and I are in a very small minority!
As for being naive, that's a pretty harsh statement. But I do think everyone should consider that whenever vast amounts of personal information is in the hands of any 3rd party, it's dangerous. Apple does seem like one of the "good guys", but:
1) management changes, the data they own never goes away.
2) security breaches occur all the time, and the more data in any one place, the bigger a target it is.
3) companies are indeed gathering more and more profiling information all the time (not just location-based)
4) when the feds do step in and make use of that data, the public absolutely does not get to know about it (this is a fact).
Now, this brings up the real elephant trying to sneak around in the back of the room: Google!
Apple is in business to sell computers, iPhones, etc. Gathering personal information is helpful to them, but ancillary. It's easy to see why they'll want to enable various features that rely on personal information, but making the vast majority of that data opt-in does not run completely contrary to their business model.
Google, on the other hand, needs to know as much personal profile information about their users as possible because it's the crux of their business. I am dying to see how Google responds to this inquiry!
If you're not willing to take 3 minutes to get as far as Step 3, I've wasted hours to try and explain. I 'm not going to bother wasting another hour on finding and posting links that you can't be bothered to read.
It's apparently only important to you as something to argue about rather than take the time to understand. And that's fine. Not everyone is curious about how GPS works, only that it does.
Ok you posted a link, I went to it, it did not mention anything about four satellites, I came back here to find that you had edited your comment saying read all the pages. My experience with the site was not good as the navigation sucks and in my opinion is a very low quality site which I would not have any more confidence in than your unsubstantiated claims that if you don't have four satellites locked you will lose your GPS fix.
Find the authoritative page like a university paper, manufacturer document etc, link to the exact paragraph, sentence that supports your claim and I will be happy to write to Garmin and ask them for an explanation on the apparent contradiction.
I wrote geosynchronous. Geostationary specifically refers to a specific kind of geosynchronous orbit at 0° latitude (equator). Geosynchronous orbits can be elliptical (as well as other types of orbits I can’t remember).
I specifically choose not to refer to them as "elliptical geosynchronous orbits” since we can’t even agree on how many satellites it takes to determine a point on a three dimensional Cartesian coordinate system.
Unless I’m missing something and you two are saying these satellites don’t continuously follow the same elliptical path.
You are correct that geostationary refers to the equatorial geosynchronous orbit, but geosynchronous still requires the orbital period to be one day. The GPS constellation is in a lower orbit, and not geosynchronous.
The debate about how many timing signals are required to determine position uniquely is pretty lively. In Euclidean space (a good approximation here), each satellite constrains the GPS unit to the surface of a sphere of radius equal to the distance computed by the time offset required to match the GPS signal.
Data from two satellites therefore constrains to the intersection of two spheres (if we don't include the earth's mean sea level as an additional reference sphere), which will be a circle with a diameter that should not exceed that of the earth itself (that nearly occurs in the case of two satellites nearly opposite each other and close to the horizon).
Data from three satellites should constrain to the intersection of three spheres, which may not exist (we disregard that solution as unphysical), occur at one point (the common unique solution) or at two points (possible but unlikely in this geometry).
However, that does not address timing error considerations, which, as have been pointed out, typically degrade the accuracy of the 3-satellite solution. Adding either the earth mean sea level sphere (approximate due to your unknown elevation), or a fourth GPS satellite sphere constrains to enough accuracy to give you a lock.
UPDATE: in case anyone is still reading - simple geometric considerations rule out the unique solution also - that would require at least one of the satellites to be below the horizon. That leaves just the problem of isolating the physically possible solution from the two points where the third timing sphere intersects the circle from the first two.
Ah, finally someone besides Solipsism that has taken the time to try and understand the whys and whatnots of GPS. Welcome to the discussion Muppetry
Thank you, and thanks for your contributions too. Actually I can't really take much credit there as I'm already familiar with most of this stuff - hence my attempt to contribute.
You are correct that geostationary refers to the equatorial geosynchronous orbit, but geosynchronous still requires the orbital period to be one day. The GPS constellation is in a lower orbit, and not geosynchronous.
The debate about how many timing signals are required to determine position uniquely is pretty lively. In Euclidean space (a good approximation here), each satellite constrains the GPS unit to the surface of a sphere of radius equal to the distance computed by the time offset required to match the GPS signal.
Data from two satellites therefore constrains to the intersection of two spheres (if we don't include the earth's mean sea level as an additional reference sphere), which will be a circle with a diameter that should not exceed that of the earth itself (that nearly occurs in the case of two satellites nearly opposite each other and close to the horizon).
Data from three satellites should constrain to the intersection of three spheres, which may not exist (we disregard that solution as unphysical), occur at one point (the common unique solution) or at two points (possible but unlikely in this geometry).
However, that does not address timing error considerations, which, as have been pointed out, typically degrade the accuracy of the 3-satellite solution. Adding either the earth mean sea level sphere (approximate due to your unknown elevation), or a fourth GPS satellite sphere constrains to enough accuracy to give you a lock.
That exceeds the scope of my knowledge. Thanks for the clear explanation.
Thank you, and thanks for your contributions too. Actually I can't really take much credit there as I'm already familiar with most of this stuff - hence my attempt to contribute.
Then it's quite possible we've run into each other before at some other site or venue. I tend to get around.
How many more links would you like? I've posted at least two professional and gps-industry specific sources as well as listed my own qualifications. I explained the source of your misunderstanding of the Garmin manual. And I've given you a test to prove me wrong.
NOTE: Be sure to read the whole thing, not just the first page. Step 3 and it's explanation of timing is important.
I don't have a useful way of performing the test, and I didn't see any links you say you provided. A link is exactly that. It's not a general statement about some site or other.
Now, you've provided a link, which I will read as soon as I finish this reply.
Ok. I would have, and did expect a more professional site, but it was ok.
So I don't see a difference between what we're saying. You can locate with three satellites, as we've been saying, but need four for more accurate location. Nothing major there. More satellites can be used for even more accurate location, as I said.
I don't see anything new there. Most of the rest I'm already familiar with.
Find the authoritative page like a university paper, manufacturer document etc, link to the exact paragraph, sentence that supports your claim and I will be happy to write to Garmin and ask them for an explanation on the apparent contradiction.
And here, the first sentence under GPS Receiver Acquisition Time. Probably the exact match for the only sentence that will apparently appease you. Quote: All GPS units require a certain amount of time to acquire 4 satellites, the minimum number needed for fixing a position (3 for space, 1 for time).
It's a good press release. Simple, clear and very direct. I appreciate the language and format and believe this will help alleviate most of the controversy and angst.
Of course there is a whole group out there that won't believe any explanation Apple puts out, to them I wonder how they live with knowing their cell company does track their movement & at times turn that info over to government. This was such a bunch of hullabaloo.
One cool thing that came out of all this, now I understand how my iPhone is giving me such accurate GPS coordinates when I appear to have no clear view of the sky! Very cool!! Hope all the complainers don't ruin this for me.
And here, the first sentence under GPS Receiver Acquisition Time. Probably the exact match for the only sentence that will apparently appease you. Quote: All GPS units require a certain amount of time to acquire 4 satellites, the minimum number needed for fixing a position (3 for space, 1 for time).
Looks like the only person here who fully understood this is Muppetry. The forth satellite apparently does nothing about elevation but is used to correct any timing issues. So what I understand is that 3 satellites gets you all of the location info including the elevation but is too inaccurate to be useful without the fourth satellite to correct the timing errors. Interesting...
Looks like the only person here who fully understood this is Muppetry. The forth satellite apparently does nothing about elevation but is used to correct any timing issues. So what I understand is that 3 satellites gets you all of the location info including the elevation but is too inaccurate to be useful without the fourth satellite to correct the timing errors. Interesting...
Thanks. I guarantee that I never fully understand anything, but at a basic level, GPS is not that complicated. One further observation regarding elevation is that due to the geometry of the earth and the GPS constellation, not all spatial dimensions are equally resolved. The best reception at any given time will be from satellites that are well above the horizon, which makes elevation the least well resolved. That is why, even with more satellites locked, horizontal accuracy typically exceeds vertical.
And here, the first sentence under GPS Receiver Acquisition Time. Probably the exact match for the only sentence that will apparently appease you. Quote: All GPS units require a certain amount of time to acquire 4 satellites, the minimum number needed for fixing a position (3 for space, 1 for time).
Very interesting. I have to note that there is disagreement between the first two regarding the maximum number of satellites visible at once. The first link says up to 12, but the second said up to 8, which as far as I know, is the correct number. I was going to work it out mathematically, but honestly, I decided it wasn't important enough to bother with. Possibly the difference comes from the 24 that were first used, and the 32 or so that are supposed to be in place now?
Both articles do say that three satellites can be used for position data in a 2D space, which, again is expected. The forth, which gives greater accuracy by computing the time data errors, also gives the Z position. What we're talking about as to our disagreement, is whether modern receivers are satisfied with using three, or will only work with four or more. I would imagine that now, they will only use four, unless there is some extreme reason not to do so. But for older models, three was common.
Thanks. I guarantee that I never fully understand anything, but at a basic level, GPS is not that complicated. One further observation regarding elevation is that due to the geometry of the earth and the GPS constellation, not all spatial dimensions are equally resolved. The best reception at any given time will be from satellites that are well above the horizon, which makes elevation the least well resolved. That is why, even with more satellites locked, horizontal accuracy typically exceeds vertical.
Right again. Vertical position errors (elevation) are commonly several times that of horizontal errors.
Comments
Overall, I was pretty pleased to see Apple's official response today. It took a little longer than I think many people would have liked, but it's generally plausible, and I still feel that Apple is generally one of the "good guys" in the realm of privacy. Minor issues pointed out here:
When they say that "Apple is not tracking the location of your phone", it may be true from a pedantic nature, but general location information about your phone was (and will continue to be if you opt to allow it) being passed along to Apple. It may not be highly accurate data, and it may have been purged or otherwise aggregated on their end to the point of not identifiable, but location data was passed on.
When they say "This data is sent to Apple in an anonymous and encrypted form. Apple cannot identify the source of this data.", I don't quite buy that. If they choose to take note of where the data came from, it could be identified, even if the identifying info is not explicitly in the data itself. Yes, this is a minor point, just throwing it out for sake of completeness.
Lastly, on this PR statement, I don't believe the two issues were really "bugs", but I could be convinced that they were simple oversights. Yes, there is a difference, although it's not really that important in the scope of explanation to the public.
But overall, these are small nits, and I applaud Apple for coming out and not only explaining what's going on, but taking steps to rectify the problems. To be honest though, they had little choice. The media and public at large were not going to let go of this easily.
They make it clear that it is anonymous. As we can see from Apple's statement today, this isn't what you insist it is.
As I alluded to above, any sizable amount of location-based data, even with no user-identifying bits, should not be assumed to be anonymous. It's possible that this particular data was not accurate enough to be identifiable, but I haven't seen anything (yet) that leads me to believe that's the case. Here is a great article, worth reading in its entirety:
http://33bits.org/2009/05/13/your-mo...ocation-pairs/
The PARC article referenced within is also good, but more technical than most people will want to read.
Because of that, using this to track people is useless, and hasn't been allowed in court so far.
Key words: so far ! ;-)
I, for one, always read the fine print so I can make educated choices.
Having said that, am I being naive?
PS: Thanks for not picking on me.
As for reading fine print, you and I are in a very small minority!
As for being naive, that's a pretty harsh statement. But I do think everyone should consider that whenever vast amounts of personal information is in the hands of any 3rd party, it's dangerous. Apple does seem like one of the "good guys", but:
1) management changes, the data they own never goes away.
2) security breaches occur all the time, and the more data in any one place, the bigger a target it is.
3) companies are indeed gathering more and more profiling information all the time (not just location-based)
4) when the feds do step in and make use of that data, the public absolutely does not get to know about it (this is a fact).
Now, this brings up the real elephant trying to sneak around in the back of the room: Google!
Apple is in business to sell computers, iPhones, etc. Gathering personal information is helpful to them, but ancillary. It's easy to see why they'll want to enable various features that rely on personal information, but making the vast majority of that data opt-in does not run completely contrary to their business model.
Google, on the other hand, needs to know as much personal profile information about their users as possible because it's the crux of their business. I am dying to see how Google responds to this inquiry!
If you're not willing to take 3 minutes to get as far as Step 3, I've wasted hours to try and explain. I 'm not going to bother wasting another hour on finding and posting links that you can't be bothered to read.
It's apparently only important to you as something to argue about rather than take the time to understand. And that's fine. Not everyone is curious about how GPS works, only that it does.
Ok you posted a link, I went to it, it did not mention anything about four satellites, I came back here to find that you had edited your comment saying read all the pages. My experience with the site was not good as the navigation sucks and in my opinion is a very low quality site which I would not have any more confidence in than your unsubstantiated claims that if you don't have four satellites locked you will lose your GPS fix.
Find the authoritative page like a university paper, manufacturer document etc, link to the exact paragraph, sentence that supports your claim and I will be happy to write to Garmin and ask them for an explanation on the apparent contradiction.
I wrote geosynchronous. Geostationary specifically refers to a specific kind of geosynchronous orbit at 0° latitude (equator). Geosynchronous orbits can be elliptical (as well as other types of orbits I can’t remember).
I specifically choose not to refer to them as "elliptical geosynchronous orbits” since we can’t even agree on how many satellites it takes to determine a point on a three dimensional Cartesian coordinate system.
Unless I’m missing something and you two are saying these satellites don’t continuously follow the same elliptical path.
You are correct that geostationary refers to the equatorial geosynchronous orbit, but geosynchronous still requires the orbital period to be one day. The GPS constellation is in a lower orbit, and not geosynchronous.
The debate about how many timing signals are required to determine position uniquely is pretty lively. In Euclidean space (a good approximation here), each satellite constrains the GPS unit to the surface of a sphere of radius equal to the distance computed by the time offset required to match the GPS signal.
Data from two satellites therefore constrains to the intersection of two spheres (if we don't include the earth's mean sea level as an additional reference sphere), which will be a circle with a diameter that should not exceed that of the earth itself (that nearly occurs in the case of two satellites nearly opposite each other and close to the horizon).
Data from three satellites should constrain to the intersection of three spheres, which may not exist (we disregard that solution as unphysical), occur at one point (the common unique solution) or at two points (possible but unlikely in this geometry).
However, that does not address timing error considerations, which, as have been pointed out, typically degrade the accuracy of the 3-satellite solution. Adding either the earth mean sea level sphere (approximate due to your unknown elevation), or a fourth GPS satellite sphere constrains to enough accuracy to give you a lock.
UPDATE: in case anyone is still reading - simple geometric considerations rule out the unique solution also - that would require at least one of the satellites to be below the horizon. That leaves just the problem of isolating the physically possible solution from the two points where the third timing sphere intersects the circle from the first two.
Ah, finally someone besides Solipsism that has taken the time to try and understand the whys and whatnots of GPS. Welcome to the discussion Muppetry
Thank you, and thanks for your contributions too. Actually I can't really take much credit there as I'm already familiar with most of this stuff - hence my attempt to contribute.
You are correct that geostationary refers to the equatorial geosynchronous orbit, but geosynchronous still requires the orbital period to be one day. The GPS constellation is in a lower orbit, and not geosynchronous.
The debate about how many timing signals are required to determine position uniquely is pretty lively. In Euclidean space (a good approximation here), each satellite constrains the GPS unit to the surface of a sphere of radius equal to the distance computed by the time offset required to match the GPS signal.
Data from two satellites therefore constrains to the intersection of two spheres (if we don't include the earth's mean sea level as an additional reference sphere), which will be a circle with a diameter that should not exceed that of the earth itself (that nearly occurs in the case of two satellites nearly opposite each other and close to the horizon).
Data from three satellites should constrain to the intersection of three spheres, which may not exist (we disregard that solution as unphysical), occur at one point (the common unique solution) or at two points (possible but unlikely in this geometry).
However, that does not address timing error considerations, which, as have been pointed out, typically degrade the accuracy of the 3-satellite solution. Adding either the earth mean sea level sphere (approximate due to your unknown elevation), or a fourth GPS satellite sphere constrains to enough accuracy to give you a lock.
That exceeds the scope of my knowledge. Thanks for the clear explanation.
Exactly I belive that the orbital period of the satelites in the GPS constellation is around 12 hours
Yes - approximately. They are up around 20000 km.
Thank you, and thanks for your contributions too. Actually I can't really take much credit there as I'm already familiar with most of this stuff - hence my attempt to contribute.
Then it's quite possible we've run into each other before at some other site or venue. I tend to get around.
Then it's quite possible we've run into each other before at some other site or venue. I tend to get around.
Me too, though GPS per se is not my field except in a somewhat broad sense.
How many more links would you like? I've posted at least two professional and gps-industry specific sources as well as listed my own qualifications. I explained the source of your misunderstanding of the Garmin manual. And I've given you a test to prove me wrong.
I'll try one more time. This one has pictures
http://www.trimble.com/gps/howgps.shtml
NOTE: Be sure to read the whole thing, not just the first page. Step 3 and it's explanation of timing is important.
I don't have a useful way of performing the test, and I didn't see any links you say you provided. A link is exactly that. It's not a general statement about some site or other.
Now, you've provided a link, which I will read as soon as I finish this reply.
Ok. I would have, and did expect a more professional site, but it was ok.
So I don't see a difference between what we're saying. You can locate with three satellites, as we've been saying, but need four for more accurate location. Nothing major there. More satellites can be used for even more accurate location, as I said.
I don't see anything new there. Most of the rest I'm already familiar with.
Anyway, I've read Apple's statement and it's exactly the information I was looking for. Good work, Apple.
* Turns iPhone back on. *
You're premature, the fix hasn't been pushed out the the public yet. ;-)
I want to know is:
Who's paying for the data transmission?
Me, AT&T, Apple or some other.
Find the authoritative page like a university paper, manufacturer document etc, link to the exact paragraph, sentence that supports your claim and I will be happy to write to Garmin and ask them for an explanation on the apparent contradiction.
This link, paragraph 5.
http://www.gpsinformation.org/dale/theory.htm
And from the University of Colorado
http://www.colorado.edu/geography/gc...gps/gps_f.html
http://www.colorado.edu/geography/gc...gps/gps_f.html
And here, the first sentence under GPS Receiver Acquisition Time. Probably the exact match for the only sentence that will apparently appease you. Quote: All GPS units require a certain amount of time to acquire 4 satellites, the minimum number needed for fixing a position (3 for space, 1 for time).
http://firebug.sourceforge.net/gps_tests.htm
It's a good press release. Simple, clear and very direct. I appreciate the language and format and believe this will help alleviate most of the controversy and angst.
Of course there is a whole group out there that won't believe any explanation Apple puts out, to them I wonder how they live with knowing their cell company does track their movement & at times turn that info over to government. This was such a bunch of hullabaloo.
One cool thing that came out of all this, now I understand how my iPhone is giving me such accurate GPS coordinates when I appear to have no clear view of the sky! Very cool!! Hope all the complainers don't ruin this for me.
Ok.... they say this and that...Fine.
I want to know is:
Who's paying for the data transmission?
Me, AT&T, Apple or some other.
That's a very good question! I want my $1.50 refund for last months data use!!
This link, paragraph 5.
http://www.gpsinformation.org/dale/theory.htm
And from the University of Colorado
http://www.colorado.edu/geography/gc...gps/gps_f.html
http://www.colorado.edu/geography/gc...gps/gps_f.html
And here, the first sentence under GPS Receiver Acquisition Time. Probably the exact match for the only sentence that will apparently appease you. Quote: All GPS units require a certain amount of time to acquire 4 satellites, the minimum number needed for fixing a position (3 for space, 1 for time).
http://firebug.sourceforge.net/gps_tests.htm
Thanks,
Looks like the only person here who fully understood this is Muppetry. The forth satellite apparently does nothing about elevation but is used to correct any timing issues. So what I understand is that 3 satellites gets you all of the location info including the elevation but is too inaccurate to be useful without the fourth satellite to correct the timing errors. Interesting...
Now as long as Mel is satisfied too then we should be done with the basics of the gps discussion, correct?
Thanks,
Looks like the only person here who fully understood this is Muppetry. The forth satellite apparently does nothing about elevation but is used to correct any timing issues. So what I understand is that 3 satellites gets you all of the location info including the elevation but is too inaccurate to be useful without the fourth satellite to correct the timing errors. Interesting...
Thanks. I guarantee that I never fully understand anything, but at a basic level, GPS is not that complicated. One further observation regarding elevation is that due to the geometry of the earth and the GPS constellation, not all spatial dimensions are equally resolved. The best reception at any given time will be from satellites that are well above the horizon, which makes elevation the least well resolved. That is why, even with more satellites locked, horizontal accuracy typically exceeds vertical.
This link, paragraph 5.
http://www.gpsinformation.org/dale/theory.htm
And from the University of Colorado
http://www.colorado.edu/geography/gc...gps/gps_f.html
http://www.colorado.edu/geography/gc...gps/gps_f.html
And here, the first sentence under GPS Receiver Acquisition Time. Probably the exact match for the only sentence that will apparently appease you. Quote: All GPS units require a certain amount of time to acquire 4 satellites, the minimum number needed for fixing a position (3 for space, 1 for time).
http://firebug.sourceforge.net/gps_tests.htm
Very interesting. I have to note that there is disagreement between the first two regarding the maximum number of satellites visible at once. The first link says up to 12, but the second said up to 8, which as far as I know, is the correct number. I was going to work it out mathematically, but honestly, I decided it wasn't important enough to bother with. Possibly the difference comes from the 24 that were first used, and the 32 or so that are supposed to be in place now?
Both articles do say that three satellites can be used for position data in a 2D space, which, again is expected. The forth, which gives greater accuracy by computing the time data errors, also gives the Z position. What we're talking about as to our disagreement, is whether modern receivers are satisfied with using three, or will only work with four or more. I would imagine that now, they will only use four, unless there is some extreme reason not to do so. But for older models, three was common.
Thanks. I guarantee that I never fully understand anything, but at a basic level, GPS is not that complicated. One further observation regarding elevation is that due to the geometry of the earth and the GPS constellation, not all spatial dimensions are equally resolved. The best reception at any given time will be from satellites that are well above the horizon, which makes elevation the least well resolved. That is why, even with more satellites locked, horizontal accuracy typically exceeds vertical.
Right again. Vertical position errors (elevation) are commonly several times that of horizontal errors.