Application Name: eGEO Compass
Description: Geological compass; measures direction and orientation of steepest slope; logs that with GPS coordinate data
Publisher’s website: eGEO Compass
Cost: Free basic version; 10 euro registration adds ability to export data, display it in Google Maps interface
Version/date reviewed: v.1.0.2 / 12-4-10
Phone/OS: Droid X / Android 2.2
eGEO Compass was mainly designed as an electronic version of a geologist’s transit. Lay it on a flat surface, and it will measure the angle and direction of the steepest slope; with a GPS fix, it will also display the coordinates. This makes it useful for mapping the angle and direction of geological strata, but that slope/direction data might also be useful to geomorphologists, archaeologists, solar panel installers, and others.
Figure 1: Start up the app, and it will prompt you for a name to save measurements under. All measured points are saved in the same data list, but can be differentiated by entering different names here. You’ll then get the display at left, that shows the direction of the steepest slope first, followed by the angle the slope dips down from horizontal (you might have to tap/shake the phone a bit to get the measurement to register correctly). Up at top are the current location from GPS, latitude/longitude. Tap on the Save button to log this data. (long-click for overturned) is mainly of use to geologists, for indicating a strata that has been flipped over by geologic/tectonic forces.
One nice thing is that it will measure the steepest slope regardless of how the phone lies on the surface. In other words, you can just the lay the phone flat down on the surface without worrying about the direction it’s pointed in.
Figure 2: To see saved data points, go to the starting screen, and go to Menu => Show Data Table. The list will only show the slope measurements, along with the date/time they were taken. Tap on a measurement …
Figure 3: … and you’ll see the full data, including GPS position. You can also add a note to that measurement point.
Figure 4: From the startup page, there’s also a Menu => Registration option that brings up this screen. This implies that registration is free, and apparently for while it was. The author now requires a 10 euro fee (about $13) to register the app; visit his Donations page to find out how to do this.
Figure 5: Registration lets you export the data table in CSV format, as well as plotting the data in a Google Maps interface.
Other issues: The app gives the slope angle relative to horizontal, which is zero for flat and 90 degrees for vertical. For some applications, it would be nice to have the slope normal to horizontal, i.e. 90 degrees for flat and 0 degrees for vertical. You can figure that out easily enough by subtracting the measured angle from 90 degrees, but a direct readout would be more convenient. Some geologists plot the angle of geological data using “strike” which is 90 degrees west of the measured slope angle; again, easy to calculate, but the option to display that number directly would be useful. Finally, the direction is given in magnetic, not true, so you’ll have to correct for your local magnetic declination.
Does what it says it will; not useful for everyone, but very useful for a few. Biggest issue I have with the app is the price; $13 for an app with this limited functionality seems a little steep, if you’ll pardon the pun. The author’s own map of registered copies indicates that only about 7 copies have been registered to date at that price. But if you plan to create multiple datasets out in the field, and need to export them to a spreadsheet/GIS friendly format like CSV, it might be worth it.