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.
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.
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.
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.
