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Archive for the 'elevation' Category

Measure Distances, Get Elevation Profiles With Survey

Application Name: Survey

Description: Distance and elevation profile tool

Publisher’s website: sys-irap

Cost: Free (ad-supported)

Version/date reviewed: v.0.7.3  /  6-23-11

Phone/OS: Droid X / Android 2.3

survey_qr

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


The Survey app is an odd mix of different functions, some of which work well and are useful, others less so.

survey_menu

Start up the app, and get three options: Measure, Short distance, and Long distance.

measure

“Measure” brings up the view from your camera (not visible in the screenshot above), along with a graduated on-screen scale and slider. The idea here is that if you know the distance to an object, you can set it using the slider, and the scale will adjust to measure the true size. Not really sure how useful this is, as it only works out to a distance of 5 meters max, and fairly small sizes. Seems to me it would be easier just to pull out a tape measure.

short_distance

The “Short distance” option brings up another camera view, and a superimposed ground line (red) and ground mesh. The idea here is that if you’ve entered the camera’s height above the ground in the Settings section, and if you put the ground line at the base of an object at the same ground level as you, you can determine the distance to the object, and use the vertical scale to determine the height. It works, sort of, but only to about a distance of 75-80 meters, and not very accurately at that. The Smart Measure app works in a similar fashion, but is easier to use and is marginally more accurate.

survey_1

 

The “Long distance” function is substantially more useful. Select this option, and you’ll get a Google Maps view with your current GPS location plotted as a base location. You can tap and drag this icon to set a different base location; unfortunately, there doesn’t seem to be an easy way to reset it to your current GPS location without backing out of this screen. The icon control at top left toggle between Google Maps/Satellite views (right icon), while the one at right centers the view on the current base location.

survey_2

A long press on a different location on the map creates a “survey point” at that location, marked with a camera icon. Press the “Survey” button at the bottom …

survey_3

… and get coordinates/elevations for base location and survey point, and the distance from the base point to the survey point. “G.H.” stands for “ground height”, and is determined by GPS for the base location, and always set to 0 for the survey point. You can adjust the ground height for either location with the button controls to the right.

point1

Tap on the camera icon, and get an augmented reality view through your camera, with the arrow telling you which direction you need to rotate the camera to have it oriented towards the survey point.

point2

When oriented correctly, the survey point will show up as a blue dot, labeled with the distance.

profile

Tap the other icon from the map screen, and get a plot of elevation from the base location to the survey point in orange. It’s not clear from the app what the green and red lines are; I believe they’re elevation plots and direct point-to-point sight lines that include the curvature of the earth’s surface, but I’m not sure.

Other issues: This app really needs better documentation; it’s not entirely clear how some of these functions work. The app description also implies that you can take geotagged camera shots of various screen views, but I couldn’t figure out how to get that to work.

Final thoughts: There’s the kernel of a good app here, and it’s worth taking a look at. But I prefer Smart Measure for distance/height measurements, and AltitudeProfiler for elevation profiles (though the latter has data download limits).




Graphic Local Elevation Displays With AltitudeProfiler

Application Name: AltitudeProfiler

Description: Displays elevation profile graph in one compass direction, graphic display in all directions.

Publisher’s website: AndroidPit

Cost: Free, but with daily data limit; paid version gives you data priority, and supports the program.

Version/date reviewed: v.1.02  /  2-28-11

Phone/OS: Droid X / Android 2.2

ap_qr

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


Altitude Profiler downloads local elevation data, and plots/displays it in several different ways.

ap_main

Main screen displays local coordinate data and heading at the top. In the data box are:

  • True heading (not magnetic – yay!)
  • Magnetic declination at your location (?N)
  • The pitch angle and percentage slope (“/”); lay the phone flat on a surface to get its slope.
  • The view rotation angle (“R”), showing the twist angle of the phone
  • Latitude, longitude and elevation at your current location.

The slider sets the distance over which elevation data will be downloaded and displayed. Default is 6 km, and unless you have a really good reason, you should leave it there, or set it even lower. While the app lets you select a distance up to 200 km, this will involve downloading lots of data, and the app developer is paying for this (not to mention your own data download time and costs).

The 6 buttons in the lower part access various data and function screens.

ap_graph

The first button shows you the elevation profile in the direction you’re facing, for the specified distance. Green vertical lines marked the locations of highest and lowest elevation in the profile.Your current position is plotted in a Google Maps view in the lower half. Move the slider to the right …

ap_points

… and the map scrolls to the corresponding position. Markers are plotted every 1 km.

ap_colors

The second button brings up a 360-degree graphic representation of slopes in every direction; the display rotates with your heading. Reddish colors are up-slope, while greens are down, and the intensity reflects the steepness of the slope.

ap_least

The third button brings up this odd display, sort of similar to the previous one in intent. Here, it’s displaying the “difficulty of travel” in every direction; the fastest way to travel is to move in the direction with the minimal amount of yellow overlay (here, W is the easiest path, with SE a close second).

ap_airplane

Fourth button brings up an augmented reality view, with an airplane-like HUD overlaying a camera view (which you can’t see due to the limitations of screenshots). Heading, roll and pitch are displayed. IMO, the least successful and useful screen.

ap_map

Fifth button brings up a Google Maps view, with your current location plotted as the starting point. Scroll the map in any direction …

ap_scroll

… and see a line of points plotted from your original location to a new one. Press the middle button at the bottom (the square with the zig-zag in it) …

ap_local

… and see the elevation profile over that plotted line of points.

ap_scrolled

If you scroll the map to another point, and press the “select” button at the bottom, the center of the map will be designated as the start of a new elevation profile, and marked in red; just scroll the map again to set the end point. This way, you can find elevation profiles anywhere, not just from your current location. Pressing the “GPS” button will bring up back to your current location.

ap_settings

Final button brings up a panel to turn the GPS on/off (toggle the top button), and set the distance units to miles or km (toggle the bottom button).

Other issues: Lot of mixed comments on the Android Market on this app; some people complain about its interface, while others couldn’t get it to work. I didn’t have any issues with the interface, and it worked fine on my Droid X running Froyo.

Final thoughts: I reviewed an app called Elevation and Sea Depth a while back that offered similar functionality. While AltitudeProfiler doesn’t do sea depths, it offers a better display and more options for terrestrial elevation profiles. Unless you absolutely need the sea depth data, I’d recommend AltitudeProfiler as the superior app.




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.