Smart Phone GPS are they Accurate Enough?

If you are considering smart phones or tablets for field data collection you probably have this question. You should also be be asking how much accuracy you need in doing your job, and is this better than your current method.

Trimble GPS R8

Survey grade GPS, like this Trimble R8 above, has accuracies of about 2 cm and a price tag of thousands of dollars. Fortunately this level of precision is not needed for most field jobs. I you are trying to locate a utility pole, map the boundaries of a wetland, map facility locations or locating addresses accuracy of 5 – 10 meters is probably adequate.

How Accurate is a Smart Phone GPS

I have seen many claims on the internet that cell phone GPS receivers had accuracies no better than 10 meters. Those claims are out of date and misinformed. Most modern smart phone GPS receivers come with several advanced features that improves speed of acquisition and precision. They also use WiFi to indoor positioning.

First a little background about GNSS systems.  A GPS receiver calculates its position by measuring the distance between several GPS satellites. The technique used to measure the distance is called satellite ranging, in which the distance is computed from the elapsed transmission time. The receiver then triangulates a position.

There are many sources of errors in GPS the largest being the ionosphere and troposphere distortions (refractions) of radio-signals. The total error for an uncorrected signal is 10-15 meters.

Cell phones use differential corrections to improve accuracies. Most incorporate SBAS (Space based augmentation systems) such as WAAS and ENGOS for corrections. Most modern cell phones also support GLONASS and other GNSS constellations. The additional space vehicles improves the satellite geometry reducing the Geometric Dilution of Precision. Cell phones GPS receivers are assisted, which means that the satellite ephemeris data is uploaded through the internet which results in convergence in seconds rather than minutes. The accuracy of cell phone GPS is 2-4 meters.

GPS Accuracy is 2-4 meters in most current models.

Future of GPS in Smart Phones

For smart phones a major obstacle to sub meter precision is the antenna. Smart phone manufactures have restrictions on size and budget for GPS antenna. Better patch antenna could reduce sign db loss and multipath error. An improved antenna could improve accuracies 1-2 meters. Texas researchers have developed software that could reduce multipath errors from the antenna. The European GNSS system Galileo will improve GPS position to sub-meter. Precision Point positioning (PPP) technologies could become available to smart phones improving precision to decimeter range. Increase by drone, VR and autonomous vehicles will push development of centimeter precision GPS. Prices currently for L1 centimeter precision has dropped below $500.00.