iOS / Android - GPS Accuracy

[ajnunley]

What kind of horizontal accuracy can be expected using the iOS Application?

I have seen different GPS ranges online for different iPhones, but can't find anything official and was hoping yall would know.

Are these really the error ranges I should expect?
3G iPhone w/ A-GPS ~ 8m
3G iPhone w/ wifi ~ 74 m
3G iPhone w/ Cellular positioning ~ 600m
iPhone4 = ?

What kind of accuracy should be expected when the ESRI Android App comes out? (even a broad range would be helpful) Thanks!!

[admahrou]

The iPhone 4 is equipped with the Broadcom BCM4750 chip. This chip is by design is high-sensitivity and low power consumption. Which means you will get a GPS fix in the toughest environments, but the quality of that fix is not the best. At best I would imagine you could get 7+ meters accuracy (in the wide open) with the on-board receiver.

[pml]

I can speak a little on the iOS side. This requires a bit of testing that I really need to do but have not done yet so I will pass along to you how the testing might be done. The iOS API has a locationManager object that you can use to test and verify the accuracy of it's GPS module. Look for a sample xcode project that uses locationManager (not sure, maybe it has been superseded). Then you can use locationManager's horizontalAccuracy method to get a number representing what the device thinks the accuracy is. Display that number in a UITextField as you use the iPhone or iPad. You'll also want to get the latitude and longitude - might as well put them in a couple of UITextFields as well. The latitude and longitude should be checked against an NGS monument or other known control point. Now we can calculate the accuracy on our own.

Typically the locationManager object will report an accuracy of 5 to 10 meters if there is little canopy cover and the device has had 10-15 seconds to acquire a location. That does not mean this is the accuracy - check the latitude and longitude which your device is reporting against a known location and calculate the accuracy yourself.

[rmartin4]

To extrapolate on what Paul was saying, you might want to look at the Core Location Accuracy Constants. These allow you to request a minimum accuracy (from 10m to 3km) which the device will do its best to deliver.

Core Location Constants Reference

Cheers,
Robert