Ground Control: Elevation Correction for your GPS Device
27 January 2008With the release of WKO+ 2.2, we also released a not so obvious new service that we call Ground Control. A common problem of today’s GPS devices is less than desirable elevation accuracy. This is an inherent problem that plagues GPS devices which is caused by the simple fact that GPS satellites are only above you, and a proper “fix” can never be obtained below you (through the earth) resulting in accuracy that’s roughly 1/2 as good as the horizontal position. What does that mean? Elevation is the least accurate component of a GPS position.. leading to obvious inaccuracies in your data files.
Have you ever done a workout, and as you leave your door note that the elevation reads 5010 ft, when you get back to your house 45 minutes later the elevation reads 5095? Or, you do an out-and-back course on the bike, only to view the graph afterward and note that the hills have different elevations depending on which direction you were going?
Ground Control was developed to help correct this problem. We’ve supplied Ground Control with multiple data providers, the USGS and a compilation of higher resolution data collected from multiple sources, including the National Elevation Data set, and worldwide SRTM data (collected from the Space Shuttle). Suffice to say, there are literally hundreds of gigabytes of terrain information at your disposal so you can correct your GPS files based on your horizontal position.
The service is now integrated into WKO+ 2.2. You must be a TrainingPeaks.com subscriber to access the Ground Control service, but you can also use the USGS data set to get improved data even if you are not a TrainingPeaks subscriber. To access the feature, simply right click any range on the Graph page when viewing a workout in WKO+.
Right-click any range to access the “Fix Elevation Profile using GPS…” option
A dialog box appears and allows you to submit the workout to the web service for correction. After a few seconds (using Ground Control) or a minute or so with USGS, you’ll get a corrected set of data points back. You can choose to accept or decline the corrected elevation data. Most of the time, you’ll want to keep it, especially if you live in a moderately populated area, where Ground Control data is most accurate. You can also choose to just edit sections of your workout at a time. Do this by highlighting a given “range”, then right-click the range to access the Fix Elevation feature.
After the correction has been completed, you can compare the results of the corrected data (yellow) to the original elevation data (orange).
Another very cool feature of WKO+ 2.2 is the ability to manually override the grade/elevation of a range in a workout. This is particularly useful when you use a treadmill and wear a heart rate montor or GPS device that has barometric altitude. Barometric altimeters are subject to fluctuating pressures, and thus, even while inside you’ll see a highly fluctuating elevation despite going nowhere. GPS devices don’t work at all for elevation indoors, so it’s a very handy feature to be able to select your workout and simply set the whole workout’s elevation to xxxx feet. After all, you just spent 45 minutes on a treadmill, you can be pretty sure your elevation was constant during that period! If you ran at a particular grade on the treadmill, you can set that too!
Here you can select any range, then manually “fix” the altitude and grade as you wish. Great for treadmill workouts that are flat or at a constant grade.
Why all the elevation correction tools? With the release of WKO+ 2.2, we have introduced a revolutionary new parameter called Normalized Graded Pace, and Running Training Stress Score. In essence, NGP is able to tell you that while running up a hill at 12:00 pace, your equivalent pace on the flats would be 10:15. Running TSS (rTSS) provides an overall “score” for your workout which gauges in a single number how much stress you put on your body for a particular workout. NGP is sensitive to elevation, thus, having the best elevation data possible is very important for getting accurate NGP and rTSS values.
These tools are valuable with both GPS based devices like the Garmin Forerunner, as well as barometric altimer devices like the Polar RS800. You can’t use Ground Control unless you have a GPS device, but NGP and rTSS work great with non-GPS based speed and distance devices.
Raw elevation from a Garmin EDGE on an “out-and-back” course. Note the elevation differences in the first hill climb.
Here it is after it is corrected with Ground Control . Note the “mirror-image” of the file which is what is expected.
To use Ground Control from within WKO+, make sure you have entered your TrainingPeaks.com username/password into the appropriate boxes on the Athlete Home page as shown below.
While you are at it, you’ll also note that you can export your GPS workout to Google Earth and fly around your workout. Fun stuff for sure, but incredibly powerful at the same time.
Enjoy!
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