If you have ever been involved with a GIS project that requires data collection using a handheld device there is no doubt that you at some point ask yourself "Is this spatially accurate enough?". Well here is some evidence that proves those little tiny GPS chips within those smart phones are actually pretty good.
We wanted to get some numbers for this idea so we took five different mobile devices (listed below) and tested their GPS accuracy against a known control point (NGS Point ID: DF4314). Our chosen devices were:
- iPad 4th Gen (16GB WiFi + LTE)
- iPhone 4S (3G)
- Motorola Droid Razr Maxx
- Garmin Colorado 300
- Trimble Geo XH 6000
What we discovered was somewhat surprising. As you can see from the list these devices vary in use from the simple smart phone for GPS navigation & driving directions, to the professional series Trimble Geo capable of providing survey grade GPS positioning. Below is a map showing the different precision & accuracy for each device in relation to the benchmark. We stood over the known control point and collected five GPS points with each device and averaged them and found the following observations as a result:
- When it comes to accuracy, you get what you pay for as it was no surprise that the Trimble unit provided the greatest accuracy when used with real time corrections.
- Most of the devices, such as the Motorola, had good precision but lacked in accuracy.
- All devices, except for the Trimble, missed the mark in the northwest direction.
- The uncorrected data from the Trimble provided very high precision but low accuracy.
- The iPhone was all over the place on its readings but came within 4 feet of the target when the points were averaged (that's outstanding!)
- In general, the iOS devices outperforms all of the competition when averaged except for the professional grade systems
So what does all of this show us? It proves that you still have to pay big dollars (+$10k) to get a "high accuracy" GPS device but you can make an awfully strong case for a $600 iPad with the right data collection app. Who knows, maybe the day of "survey grade" accuracy in a smartphone is in the very near future.
A pile of GPS mobile devices sitting atop our known control point.