GPS Accuracy

Because you can't fake accuracy...

You can fake your way through a lot of things in life.  For example, you may be able to fool some folks into thinking you are a baseball expert by coaching a little league team.  Make sure they know the steal sign, teach 'em to catch the ball, and not to swing at anything above their chin... and somehow everyone thinks you're some kind of pro.

So you don't necessarily have to be incredibly knowledgeable about the game or have pitched in the minor leagues to navigate your team through the season.  But there are some things you can't fake, and one of them is GPS accuracy...

Like most GIS folks, you need a good quality GNSS receiver that connects to your mobile device via bluetooth?  Most GIS folks don't need extreme sub-inch accuracy for their mapping project but they do want something that's better than the 8-10 feet they might see from their smartphone or tablet.  Something in the middle like 3-4 feet would be nice (this area is shown to be a missing option as seen in this former post on GPS accuracy).

So let's take a look at some of the latest devices out there available in this realm...

The Trimble R1 GNSS receiver packs a lot of punch into such a small box.  With Bluetooth capabilities for even more versatility.

The Trimble R1 GNSS receiver packs a lot of punch into such a small box.  With Bluetooth capabilities for even more versatility.

1. Trimble R1 GNSS Receiver-  a rugged, compact, lightweight GNSS receiver that provides professional-grade positioning information to any connected mobile device using Bluetooth® connectivity.  Cost =. $2500

2. SXBlue II GNSS- The SXBlue II GNSS is a palm-sized receiver that delivers real-time, high accuracy performance using GPS/GLONASS satellites and free SBAS corrections.  Cost = $2895.

3. EOS Positioning Systems Arrow Series 100 -The Arrow series 100 provides submeter accuracy for comparing with these other models but their line also includes the 200 model which claims to be the world’s first GNSS receiver able to provide 1cm real-time accuracy directly to your Android, iOS and Windows mobile device when connected to an RTK service or base station.  Cost = $2995.

There are many different combinations and ways that you can collect high-accuracy GIS data with mobile devices.  If you're looking for something that is lightweight and filled with performance, one of these units might be just what you are looking for.  We hope to provide some more specific examples and possibly some accuracy reviews (nothing fake) in a future post.


So what's my accuracy??? Mobile Device GPS with iPad, iPhone, & Android

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:

  1. iPad 4th Gen (16GB WiFi + LTE)
  2. iPhone 4S (3G)
  3. Motorola Droid Razr Maxx
  4. Garmin Colorado 300
  5. 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:

Click here for map of plotted points

  • 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.