Take the 2-minute tour ×
Android Enthusiasts Stack Exchange is a question and answer site for enthusiasts and power users of the Android operating system. It's 100% free, no registration required.

I was in London last week (which is outside my country, so I did not use roaming to connect to the internet to be able to use the maps application from Google). In stead , I used Mapdroid to find my way around the center there.

Mapdroid, for those who don't know this program, lets you download maps and than use them without data connection. The only thing you need to do is turn on the GPS.

This works great apart for the fact that it can take between 5 and 10 minutes for the program to mark you location. If it does, it can track you fine , and it keeps tracking you on the map.

But I am just wondering why it takes so long before Mapdroid knows where you are.

Is it a hardware thing (I have a Samsung Galaxy S phone running Froyo).

share|improve this question
    
I think this is a GPS-thing. They are slow when you start up on a new location. –  Jonas Feb 8 '11 at 9:11
    
It's most probably a hardware problem. See this question on the i9000's GPS quality: How can I fix the GPS on my Samsung Galaxy S? –  ce4 Sep 4 '12 at 18:50
add comment

3 Answers 3

up vote 11 down vote accepted

This shows the difference between AGPS and GPS. AGPS (Assisted GPS) uses a small amount of mobile data to establish a rough location fix (about 1km-100m accuracy) based on the cell towers near you. This gives a faster initial location fix than just GPS. Since you had roaming disabled, AGPS wasn't available and getting a location fix on just GPS can take a while, especially on some firmware versions of the Galaxy S.

share|improve this answer
    
5-10 minutes seems awfully long. Using a GPS receiver like a Garmin in a car takes maybe a minute at the most. Usually they only take longer if line of sight is poor. I tried Mapdroid in Vancouver and it took quite a while to sync up. It never took me 5 minutes or more though. –  Bob Feb 8 '11 at 13:39
    
Exactly right. The SGS has GPS problems up the wazoo. –  Matthew Read Feb 8 '11 at 15:10
1  
Most GPS devices (including Android) "cheat" by using their previous known location to get faster first fix. If you turned off your GPS device, and then moved to a very far away place, and turn it on there, the GPS have to locate from zero information and it will take about 5 minutes for any GPS device to get a another first fix. –  Lie Ryan Feb 10 '11 at 7:46
add comment

I've actually been writing an application that uses GPS, so I can shed some light on this. onik is correct about the AGPS vs GPS. Additionally, though, GPS can be affected by a number of factors which can reduce accuracy or the ability to receive a signal at all:

GPS accuracy is affected by a number of factors, including satellite positions, noise in the radio signal, atmospheric conditions, and natural barriers to the signal. Noise can create an error between 1 to 10 meters and results from static or interference from something near the receiver or something on the same frequency. Objects such a mountains or buildings between the satellite and the receiver can also produce error, sometimes up to 30 meters. The most accurate determination of position occurs when the satellite and receiver have a clear view of each other and no other objects interfere.

As well with AGPS is DGPS (Differential GPS). (But I do not believe phones have this, only AGPS).

Like the AGPS, the DGPS uses a fixed GPS location (such as a cell tower) to send information to the GPS receiver. DGPS, however, looks at both the satellite and the fixed location adjusts for any difference between the two, and then sends that information to the receiver. DGPS is particularly helpful when atmospheric conditions interfere with reception.

Source/more information.

In short, make sure you are outside and have a clear view of the sky. The initial lock will sometimes take quite a bit of time, but subsequent locks shouldn't be nearly as bad.

share|improve this answer
add comment

Galaxy S has a notoriously bad GPS. I Changed from S to now S3, and there is a HUGE difference. The S3 is extremely fast to get a GPS lock, and incomparably more precise. So don't expect wonders from a Galaxy S.

share|improve this answer
    
See android.stackexchange.com/a/25533/15713 –  ce4 Sep 4 '12 at 18:56
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.