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I was wondering how accurate is the GPS is in my HTC Desire Android compared to a dedicated hand held GPS unit or in car satnav?

The reason I ask is that I have read articles complaining that the iPhone's GPS is not very accurate and wondered if it applied to all mobiles.

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Also note that apps like Google Maps give you an (in)accuracy circle on the screen. When Google Maps doesn't have a very accurate location fix it will expand a blue circle out to cover the area that you could be in. When it reverts to just a blue dot then it has a good fix. –  GAThrawn Jul 20 '10 at 15:04
    
I don't think that the iPhone's GPS is less accurate. I am pretty sure what you are reading is that the Apple Maps app is not accurate. –  ZnewmaN Jan 28 '13 at 18:39

3 Answers 3

The GPS chip used in the Android devices (usually SiRF Star 3/4) are of civilian grade. Civilian grade chips has some deliberate limitations in par with military grade chips. The civilian chips does have some intentional errors called "Selective Availablity".

Hence, whether it is Android or iPhone or Bluetooth GPS receiver or a dedicated unit which could be handheld or the one in car comes under civilian category which cannot be more accurate than 20 meters under the best possible satellite lock (of course, with AGPS it can be improved). Please check the Wikipedia article which says "...improving the precision of civilian GPS from 100 meters (330 ft) to 20 meters (66 ft)."

iPhone uses BroadCOM's BCM4750 chip and Android phones (Samsung Galaxy S2) uses SiRF Star 4.

Interestingly, a web page claims "The published steady state position accuracy of the BCM4750 is 2m.", which in my opinion could not be correct. In this research publication it is said as "iPhone 4 exhibits an offset (of about 20 metres)", which seems to be more scientific and correlates with the Wikipedia page.

However, all these talks are about hardware aspect only. It is the software that reads the input from chip, processes it and displays. If it is not doing a good job, well, still it spoils the show.

So, finally my answer would be again be a question "If all these civilian GPS devices cannot be accurate by more than 20 meters, does it mean anything to say X is good and Y is bad? ;-) "

Update Thanks to @Ropo I observe that Selective Availability is indeed removed. Here is the official statement, which says:

Selective Availability (SA) was an intentional degradation of public GPS signals implemented for national security reasons.

In May 2000, at the direction of President Bill Clinton, the U.S government discontinued its use of Selective Availability in order to make GPS more responsive to civil and commercial users worldwide.

The United States has no intent to ever use Selective Availability again. In September 2007, the U.S. government announced its decision to procure the future generation of GPS satellites, known as GPS III, without the SA feature. Doing this will make the policy decision of 2000 permanent and eliminate a source of uncertainty in GPS performance that had been of concern to civil GPS users worldwide.

Please take a look at a question at StackOverflow as well.

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Nice, thank you for leading me to this answer! +1 –  Zuul Sep 12 '12 at 10:55
    
Just to mention that Selective Availability was removed in 2000. –  user27477 Jan 28 '13 at 16:23

I have an HTC Kaiser (AT&T Tilt) that I had Google Maps installed on. Google maps gave me the number of satellites that it could see in parentheses at all times. When I used my phone's internal GPS, I would get about 4 satellites, when I would use an external Bluetooth GPS, I would get about 12 satellites. When I use my TomTom, I get about 7. The number of satellites is the biggest deal for getting good location; the more the better. I never tried an external GPS antenna on my HTC Kaiser to see if it was just the antenna that was the issue or if it was something else.

The program called "GPS Status" available from Google Play Store, will show you how accurate your GPS is at any given time. The number of bins with green bars in them is the number of satellites that your phone can "hear/see" at any given time and then it also gives you the accuracy in meters on the display.

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+1 for "GPS Status" –  Jonas Jul 21 '10 at 22:04
    
My FreeRunner could see about 7-12 satellites most of the time, depending on cell tower signal (it has AGPS) and location. –  Broam Aug 9 '10 at 16:37
    
@Broam is that a gta02? What distribution? –  ott-- Jan 29 '13 at 13:37

Assisted GPS (AGPS) chips that you find in most cell phones require some assistance from the cell phone network (the towers) to get an initial fix. No matter how accurate they are, they won't work well without a cell tower in range compared to a stand-alone GPS chipset.

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Assisted-GPS is a fully standalone GPS chipset; it does not require the cell network to get an initial fix (though the existence of cell network will be used to improve the time to first fix). –  Lie Ryan Nov 12 '10 at 2:09

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