Tips for GPS Improving Accuracy When Running
August 2, 2010 by Bryon Powell · 18 Comments
Through the years, we’ve heard more than our fair share of gripes about accuracy of wrist-mounted GPS devices. We’re not buying most of them. Sure, some of the earliest models, such as the Garmin Forerunner 201/301 were quite finicky, but most models introduced in the last half decade or so are more than capable… if you treat them right. Here are some tips to help you get the most out of your GPS.
First off, make sure the unit has the latest software for both the unit and the GPS chipset. For Garmin products, these are two different updates.
Before setting out on your run, leave the unit in clear view of the sky for 2 or 3 minutes. If you can check the status of the satellite connections, do so before you run. [More for Garmin 205/305 users] Sometimes you can reorient the device to pick up additional satellites that you wouldn’t have acquired had you simply laid out the device. Even though a GPS unit will “acquire satellites” based on four satellites, locking additional satellites improves accuracy and reduces the chances of fully losing your GPS signal under trees or among sky-obscuring terrain.
Check on the GPS satellite status during the course. If possible, pick up new satellite locks en route. Do this especially after passing through forested areas or canyons or when a particular peak has obstructed a large portion of the sky for a while, such as when traversing the side of a steep mountain. You can do this by consistently holding the unit’s antenna toward the sky will moving… or repeating tip 2. The latter is easier and, if you still have some satellite locks, takes less time than before heading out.
If you are able to view a graphic representation of locked and unlocked satellites on your unit, use this screen to help out picking up lost signals by orienting the unit’s satellite toward the direction with the most non-locked satellites (unless there’s a huge obstacle blocking that direction). Be aware that even with a clear “view” of a satellite signal, it can take the better part of an uninterrupted minute to obtain a lock, so be patient.
While it won’t make your GPS more accurate, you can sometimes force a GPS unit to take measurements more often. For instance, a number of Garmin’s wrist top units, such as the popular Forerunner 205 and 305 models, allow you to set the unit on (1) “smart recording,” which varies the measurement rate based on speed, rate of direction change, etc, or (2) to take a measurement every second. Smart recording usually takes a point every couple seconds, while the other option is self-explanatory. Generally, smart recording is plenty accurate and the “every second” option only useful to a race director measuring a course or a similar, but uncommon usage.
If the “every second” method is used, it would be wise to run the data through a smoothing algorithm afterward or slight data variation in GPS points will lead to extra distance. Variation from a unit with great accuracy, say +/- 10 feet, adds up quickly. Note that a unit’s memory fills up much more quickly in “every second” mode, so be sure you need those extra points.
Once you’re back at home, software can further improve your data. For instance, if you upload the data to Garmin Connect, the “Elevation Correction” algorithm does a great job of cleaning up the elevation data. Garmin Connect has automatically applied Elevation Correction to all workouts uploaded on or after April 1. You can manually apply the correction to previously uploaded workouts via selecting “Elevation Correction” under “Additional Information” in individual workouts. This can make a HUGE difference. For example, Elevation Correction reduced an all-day snowshoe outing from 3,991′ of elevation gain to 669′. Those who used Motionbased.com prior to its merger with Garmin Connect might know this feature as “Gravity Correction.”
Call for Comments and Questions
Have you had any frustrations using a GPS during your runs? How about the opposite – has a GPS ever come in particularly handy on the run? Do you have any tips for improving the accuracy of a fitness oriented GPS-unit?
- Hit the mode button;
- Press down twice and hit enter to select Navigation;
- Press the up arrow once and hit enter to select Satellite;
- You will now see a visual representation of which satellites are or are not locked and where each is located in the visible sky. Locked satellites are a filled oval, while an empty oval is a non-locked satellite. A flashing oval means that the unit has recently received a signal from a satellite, but has not yet acquired a lock. This screen can be useful in aiming the unit to pick up additional satellites.
- Hit either the up or down arrow to see a bar chart of satellite strength. As with the sky view above, a black bar means there's a lock; however, an empty bar means the unit has received a signal, but is not yet locked. A number at the base of the chart with no bar above it means that the particular satellite is in the visible sky, but the unit has not recently received a signal. The top of the chart also shows the unit's current accuracy. If you see tall, but empty bars that don't disappear, keep your unit oriented in the same direction to pick up the satellite(s). However, if you've had you unit on for a minute or more with no bars (or no new bars) visible, move the unit or orient it toward another portion of the sky.]