In the field: Is that an iPhone in your pocket?
Being avid Cartegraph blog followers, I know you’ve all read posts on how smartphones are assisting building better communities, and how tablet computing is redefining the way we view mobile computing. Smartphones and tablets are hot! And based on my totally unofficial statistical analysis, these technologies are going to have a 4,500% (+/- 4,500%) impact on how government operates.
So not being one to buck trends, I don my expertly crafted sheep-suit and offer up the following question to ponder: Are smartphones and tablets accurate enough to be used for GPS coordinate collection of your assets in the field?
Since we’re now all experts on the relative accuracies for GNSS(Global Navigation Satellite System) Handheld Computer / Receivers, how do smartphones and tablets measure up? The quick answer—they come up a bit short in comparison.
While smartphones and tablets have a bag of location tools they can draw upon (A-GPS, Wi-Fi positioning, and cellular network positioning), the technology has been designed to provide basic Location-Based Services, such as pinpointing the nearest Starbucks, or showing your office building on a map.
A quick summary of the methods an average smartphone or tablet employs to determine its location on the face of the earth may provide additional insight:
Assisted GPS (A-GPS)
A-GPS is essentially the same technology found in GNSS Receivers, but typically the GPS chips found in a smartphone are not of the same quality as those found in a GNSS Receiver. Nor is the GPS antenna of the same quality found in higher-end GNSS Receivers.
A-GPS gets a little more bang for its buck over its brother, plain old GPS, by using the inherent network connectivity of many smartphones and tablets to get information on GPS Satellite locations, precise time values, and locations of cell towers in use – all ingredients for a more accurate GPS fix.
Wi-Fi Positioning
Like it or not, large corporations like Google, Skyhook, and others have found that it’s very profitable to find Wi-Fi access points and determine their approximate location. Cellular providers leverage these inventories of known Wi-Fi Access points and coordinates, and use them as a fast way to determine location of a smartphone or tablet.
NOTE: If this information raises your eyebrows, check out WiGLE.net! If not, odds are the men in black are installing the surveillance cameras in your home as you read.
Cellular Network Positioning
The location for wireless towers is known, and those coordinates are typically highly accurate, so using a method called “multilateration,” based on the concept of triangulation, cellular providers can provide a third measurement of where the smartphone or tablet is located.
With this said, however, both software and hardware design give traditional GNSS Receivers an edge when it comes to GPS accuracy; it’s what they were designed for. This is not to say that if you happened to be in the middle of a wide open field, at a time of day with 12 GPS Satellites “in view,” with five Wi-Fi access points near you that Google got great coordinates on, and standing in-between four cellular towers , that you won’t get a fantastic GPS coordinate fix!
Everything has exceptions, and on average, the GPS points you collect with your smartphone or tablet will not be as accurate as a typical commercial grade GNSS Receiver.
At the end of the day, you need to ask yourself the question, “How accurate is accurate?” If your answer is, “Signs in the middle of the street is good enough. I need to find something for my GIS intern to do anyway,” then go smartphone!
If your answer is, “I’ve got guys digging holes in the ground based on these coordinates,” fret not. You have purchased a powerful tool that gives your field staff the ability at any time, from anywhere, to hone their Angry Birds skill set (which has an added bonus of increasing hand-eye coordination skills by 178% (+/- 177%)). And you’ll have that going for you, which is nice.
