blankblank blank




Accurate Altitude Data In Android With Get Altitude



Application Name: Get Altitude

Description: Queries webserver for accurate altitude data for a location.

Publisher’s website: room.404

Cost: Free (adware)

Version/date reviewed: v.1.2.3  /  9-28-10

Phone/OS: Droid X / Android 2.2

ga_qr
Android Market link (mobile app only)
Android Market link (browser)


GPS is capable of determining your location reliably with about 3 meters of inaccuracy, roughly 10 feet. But GPS elevation measurements are nowhere near as accurate; they can easily be tens of meters off, and I’ve seen them off as much as 100 meters (~325 feet) from the true value. The Get Altitude app queries a web service with a location you select in a Google Maps interface, and returns the altitude for that spot. I’m not sure which web service it’s using, but I believe it uses the Google Maps elevation API. If that’s the case, elevation data has a horizontal resolution of about 10 meters for most of the US, but probably worse than that for the rest of the world.

ga_1

Figure 1: Starting up the app also starts up the unit’s GPS, and plots you current location in a Google Maps interface; you have the option of either the map view (seen here), or the satellite view. Oddly enough, there’s no option to directly query the altitude at your current location.

ga_2

Figure 2: Tapping on the map brings up standard zoom buttons, but you can also pinch to zoom as well; tap and drag to scroll. A long press on the screen at your desired location brings up a pop-up window with your current location, and the altitude from the web query. Using the “Share” function, you can export this data to associated apps (e.g. Email, Facebook, etc.).

How accurate is the data? The 6800-ft. contour line on the USGS topo map is right on my property, at the edge of a steep drop-off, so that seemed like a good reference point to use for comparison. At this contour line, I measured the elevation with three different GPS units (Garmin 60Cx, Holux M-1000 Bluetooth, and the Droid X’s built-in GPS), then queried the altitude using Get Altitude (position determined by Bluetooth GPS paired to the Droid X for maximum accuracy).


Elevation source Elevation (ft.)
USGS Topo Map (true value) 6800
Garmin 60Cx GPS (WAAS) 6838
Holux M-1000 Bluetooth GPS (WAAS) 6778
Droid X built-in GPS (no WAAS) 6893
Get Altitude data (from webserver) 6795


Clear winner in accuracy was the Get Altitude app, only 5 ft. off from the topo map value, and that’s likely within the error range of both the map’s precision and the GPS position accuracy. The two GPS units with WAAS weren’t half-bad, but still well 20-40 ft. off the true value. The Droid X’s built-in GPS did the worst, almost 100 ft. off. Keep in mind that the elevation returned by Get Altitude is ground level; it won’t be accurate if you’re in a building and want your height there.

Additional program options include setting the elevation units (feet/meters), coordinate format (DD/DM/DMS), and a search function to locate geographic features.

Other Issues: Had absolutely no problems with the app.

Final thoughts: If you’ve got a good data connection, and an accurate GPS position, Get Altitude can potentially give you more accurate elevation data than your built-in GPS can. Just remember that the accuracy of the returned data will be determined by both your GPS position accuracy and the resolution of the elevation database used by Get Altitude.


Looking for something else? Enter some keywords below, then click "Search".    




2 Responses to “Accurate Altitude Data In Android With Get Altitude”


  1. 1 ruidh

    Over water it apparently gives the depth of the water. Not entirely helpful for me.

  2. 2 Winfried

    I like this app and often use it. Last time I measured the altitude in the middle of a lake in northern Germany. It showed -3 m, the correct height is +1 m above sea level. How is this to explain? Is it the normal incertitude or has it to do with “water”, may be the app measures from the bottom of the lake?