Why is the GPS so stupid?

B

blackheartred14

New member
Trying to use the GPS in an area with no cell towers means that the stupid GPS takes MINUTES to find a position each time the power-save goes on.

Why can't it use the last known position as a starting point?

I was in Europe without a GSM phone, but I could just as easily have been in the woods somewhere without cell service.
 
Someone correct me if I'm wrong, but if there is no cell service, you should turn off the "use wireless networks" in the location settings, and make sure that "use gps satellites" is turned on. That way it will only use the satellites to track you - not the cell towers.
 
Count yourself lucky. In the mid 1990s it took about 15 minutes to get a lock, every single time.

Modern GPS systems are capable of getting lock pretty quick (under a minute) as they do use the last known location. However, this only works if they have up to date almanac information downloaded from the satellites. This becomes out of date in about 1 to 2 weeks, and needs a good lock with a clear view of the sky (no buildings, roofs, or tress in the way) for about 15 minutes to be sure it's updated.

If you do that (get a good lock for 15 minutes), then put the phone in standby and back again, how long does it take to establish a lock?
 
If there's no cell service, you should still leave wireless networks checked. In fact, I recommend folks leave both the GPS Satellites and the Use Wireless Networks checked.

Wireless networks could be any form of data, whether it be cell or wifi -- it's technically called AGPS.

GPS Satellites are excellent for finding yourself accurately within 5 feet. What Android does is it caches your last found location. It only will ask for the position again if it's outside of a defined parameter by the developer.

So, for my apps I typically say you need to be within a 1000 foot threshold. After the first look up from a position, any subsequent position after that look up but within the 1000 feet should be very quick (although less accurate). However, there's also a timed expiration. So if you haven't moved within the last 10 minutes from within the 1000 foot radius (for example), it'll probably do a fresh look up.

Using wireless networks is a faster look up, however GPS is more accurate but requires you have some view of the sky.

EDIT: And just a few years back a GPS lock on took about 30 seconds - 1 minute. My G1 for pure GPS is about 5 seconds.
 
GPS is dependent on whether you can see the sky clearly, and the weather conditions (rain, snow, etc). If you have GPS turned on, it should be relatively fast unless you're not within view of the sky. Using wireless networks, called A-GPS, is dependent on cell towers. So, if you are in the woods in the middle of nowhere, you should be able to find your position without the network as long as you can see the sky.
 
I think there's some confusion here as to what AGPS actually is.

AGPS, at least in the context of mobile phones (see the Wikipedia article on it for how AGPS can be used in other systems), is where the GPS uses the coordinates for the cell site towers you're currently using to provide a course location to the GPS system. This is then used to calculate which satellites should currently be visible to the phone, and hence it can prioritise looking for a signal from those satellites instead of wasting time trying to find the 30 odd others, so it gets a lock much more quickly. Some older stand-alone GPS systems used a similar system by asking you what country you were in on startup. This is equally effective, but not automatic. AGPS on Android phones doesn't use WiFi at all.

There is a system called SkyHook which both Android and apps running on Android can use for position location. This system combines the following three positioning systems, and is where WiFi comes into the picture:

* GPS (accurate outdoors, slow lock time, doesn't work well indoors)

* WiFi (locations of known WiFi locations by MAC address - fast, but only works very near to WiFi points that are known to Google/Skyhook)

* Cell tower location (only works if you have a phone signal, inaccurate, instant information)

This is not AGPS though. This is SkyHook.
 
Thanks for the informative post.

What apps use Skyhook? Is it up to the app developer?

Do you have any idea of the global nature of the MAC address database used by Google/SkyHook? Is Europe included? Asia?

In my little experiment in Europe I did not have WiFi turned on while I was wandering outdoors, but I did have an unobstructed view of the sky.

I will repeat the experiment here, getting a lock outdoors, then turning off wireless networks, put the phone in standby, then try again to get a lock ..
 
I wouldn't worry about turning WiFi off. If there's no WiFi around nothing will happen. If there is WiFi around you may get a reasonably accurate (30m or so) position.

It's up to the developer as to whether they use the SkyHook API or not. I know the app Locale does, but just about any positioning app could. It's not easy to tell from looking at the app. I only know Locale does because it allows you to submit unknown WiFi locations to SkyHook.

SkyHook is available in every country in the world, but it doesn't know about every WiFi point in every country. The Google StreetView cameras also recorded WiFi position information when they photographed the streets, so the places that have StreetView (at least more recently anyway) have full coverage. You can check the coverage of WiFi points here: http://www.skyhookwireless.com/howitworks/coverage.php

Android itself seems to have some relationship with SkyHook, as from 1.6 onwards the wording of the "Use wireless networks" option in the settings changed to include the bit in bold "Location determined by Wi-Fi and/or mobile networks". Also the option "Share with Google - Allow Google to use location for improved search and other services" appeared. I know that "other services" includes traffic information (if you and lots of other people are on a road and going 30mph less than the speed limit they know there's a delay, if you're stationary they know there's a problem) which they use on the traffic layer on Google Earth and Maps. They also add WiFi locations that are unknown to them if you are near a WiFi point that's not in their database and you get a GPS lock.
 
Looking at the map is mind-blowing -- look at Europe. Skyhook seems to have cached MAC addresses only west of the prime meridian! (exception: the sole of the Italian "boot"). I cannot imagine how that came to be...

Added - the abrupt cutoff at longitude 0 is a figment of the display. When it is zoomed up this boundary disappears.
 
The areas of high coverage are all areas (as far as I can tell) that have had more recent Google Street View cameras driving around them. There are other areas that are covered too - some hotel and restaurant chains that provide wireless access are shown. Also people may submit their own MAC addresses on the SkyHook website, so there are little dots that appear all over the place.
 
Look, bottom line? If you are traveling and want accurate, fast positioning, use a dedicated GPS device. I just got back from Qatar and was outside on a perfectly clear day, I with my G1, friend with his iPhone. We both simply gave up on waiting for a GPS hit. Could have turned on data but then I'm roaming so, no thanks. Even so, the network positioning on my phone has proved to be so inaccurate I will never trust it.
 
The GPS units in all Android phones and the iPhone are perfectly fine, and in most cases the same chipsets that most dedicated sat navs use. Of course, they can't see through the metal roof of your car, so you need a suction mount for them, just like a dedicated sat nav would use, so they can see upwards through the glass.
 
While there aren't enough satellites at the moment for the highest quality coverage in all locations, they orbit very fast. If you don't have great coverage one moment, you will 5 minutes later. You should still have good coverage (6 or more visible satellites) all the time. You only need 4 for a lock.
 
I am using Garmin XT on Nokia E71 - never had problems; it takes maybe up to 30 seconds to acquire satellites with or without internet and/or cell phone reception (network)... it simply acts like a stand alone navigation.
 
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