Question about GPS accuracy and the iPhone 4

[TheBlindGeek]

Hello,

I've been an iPhone 4 user for just about a month now, and noticed something that I'd consider a bit odd... When I use apps that need to know my location, the information I get back from my iPhone 4 seems to vary a bit at times. I'll give an example... I was traveling from downtown Seattle to my house in the southwestern part of the city, and since the bus I was riding on didn't have a properly functioning automatic stop announcement system (it calls out most stops with a recorded voice, useful for a blind or visually impaired person like myself or those unsure of the stop they might need), I used one of the navigation apps I had installed to make sure I got off at my stop. For the majority of the trip, nothing seemed amiss, but once I got close to my house (within 300 feet of the corner nearest my house), I noticed that the information I got from the app was slightly inaccurate. Instead of informing me that I needed to turn in 300 feet or so to arrive on my street, it told me to turn immediately to the right to arrive on my street... which if I had followed the iPhone's directions blindly (no pun intended), I would have wound up in someone's front yard. I did continue to what from what limited vision I do have, what would be the intersection and made the turn down my street toward my house, but before I could get more than a few feet down my street, the iPhone informed me that my destination was on the left. Of course, this was wrong, as consulting the Compass app when I got home, I discovered that my house is actually 219 feet from the corner, roughly about mid-block.

I'm not sure if Navigon was at fault here, or the GPS hardware in the iPhone isn't working right, but I do have to ask, since apps like Foursquare seem to be a bit more accurate most of the time. I wonder if it could be the way I'm holding my iPhone, a misbehaving GPS chip, or some weird fluke of my neighborhood in Seattle (it's fairly close to a small airport, but sits considerably higher in elevation). Anyone else out there having issues with the accuracy of information their iPhone gives them when using GPS, or is it just me?

 

[kch50428]

The accuracy of a GPS receiver in a phone, or a stand alone unit for that matter - is going to be plus or minus 10 feet or so in the best of circumstances and often is more like 30 feet or more.

Often, iPhones use "Assisted GPS" in addition to the phone's hardware receiver - the assisted function will use a wifi node's location to assist in giving the phone and apps location data...this is where errors can creep in - if you are connected to a wifi node who's known location is not accurate - your location will appear off. Cell phones can also use location data derived from the cell phone network - which can also be a source for inaccuracy as the cell network may not be properly set up to deliver accurate info as well... and yet another source for inaccuracy is how GPS apps determine a specific address on a given block - they know the address range on a street, and kind of guess where a specific address is on a street.

 

[icebox93]

I've found when watching the gps at the most detailed settings on the map will occasionally show we're riding off the road when that is not the case. And the GPS mapping function in the Map My Ride app will occasionally show me off the bike path when that is not the case either. But these sorts of errors are of the 10 to 15 feet variety, certainly not 100-200 foot errors. I haven't ever had my phone report that much of an error.

 

[macsethi]

GPS works perfectly. Its very accurate and almost error free. The absence of clear sky might make the app use wi fi or data connections to estimate the local which surely causes errors.

 

[kch50428]

GPS works perfectly.

There's no such thing as perfect in GPS hardware in cell phones. There are inherent issues to overcome that would make the cost of a cell phone prohibitive to average consumers too make a cell phone with the capabilities to as much as is possible overcome those inherent issues.

 

[stevesmart]

The technology just isn't as good as it will be in 10 years, sadly. There is an element of assumption when using the Maps app - if you're following a road, the iPhone will usually keep your location locked onto that road for "convenience".

 

[Engire]

I use the Mapquest app and it seems to function well. I will confess that I did know where I was going and use it more for experimental purposes but it seemed fairly accurate.