Application Name: Rocklogger

Description: Map slopes and which direction they’re facing.

Publisher’s website: RockGecko

Cost: Free evaluation version limits you to 3 measurements every two minutes; $9.22 fee unlocks this restriction.

Version/date reviewed: v.1.01  /  3-27-11

Phone/OS: Droid X / Android 2.2


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

A while back, I reviewed eGeo Compass, an app that maps slope and slope direction. The primary use is for geological mapping, but it could be used by anyone who has similar mapping needs (geomorphologists, archaeologists, gardeners, etc.). I thought eGeo Compass was pretty good, but the demo version was limited in functionality, and the registered version was a bit expensive at $13. Rocklogger offers the same basic functionality, the free version does more, and the registered version is cheaper, but it has some drawbacks as well.


App starts with the barest of screens. Tapping on Start new traverse brings up the option to name the data file, and also associate additional information. Unlike eGeo Compass, the free version of Rocklogger will let you export data in CSV format for use in mapping programs. If you’ve already stored a data file, you can also select it, and append new data points.


In measurement mode, the app will fire up the GPS to get your current position, and then display your current coordinates, along with your choice of three kinds of measured data:

  • Dip angle and direction: The slope in degrees, and the compass direction of that slope (you can choose true or magnetic direction)
  • Dip/strike: Commonly used in geological mapping. Dip is as above, but strike represents the orientation at which a geological strata intersects the ground surface; usually it’s 90 degrees less than the dip direction.
  • Magnetic field mode: Measures and records the magnetic magnitude vectors (XYZ), and the absolute magnitude

When you’re ready to make a measurement, lay the phone on the surface you want to measure, oriented so that the long axis of the phone (up/down) lies along the steepest slope).


Tapping on the Plane Type dropdown brings up a preprogrammed list of geological features you can assign to the point. However, you can add your own types (including non-geological ones), and subtract ones currently on the list, customizing it to your own requirements. The Settings section lets you reset this to the default. The Setttings section also implies that the app can save Rock Type input and let you choose from suggestions, but I couldn’t get that to work, possibly because I’m not using the default Android keyboard.

Pressing the Save incl. sensors button saves your current position and the measured data into the current data file; Save excl. sensors saves only your current position. You can set the app to require a long press to save data, to prevent accidental data recording. The evaluation version limits you to no more than three measurements in two minutes; the registered version allows unlimited measurements within any time frame.


Use the Back button to stop measuring, and bring you back to the startup screen; there now should be a listing for the new data file. Tapping the listing for that file name brings up the option to add more points, delete it, email it (useful for backup in the field, or exporting it to your computer for additional analysis), or open it in a compatible app for viewing/editing.

Other issues: Unlike eGeo, Rocklogger doesn’t currently have the option in either the free or paid version to plot recorded data in a Google Maps view, though the author indicates this is coming. Having latitude/longitude displayed in degree-minute-seconds, without the option to view it in decimal degrees, is annoying; fortunately, positions are saved in decimal degrees in the data file.

The biggest issue for me is that, unlike eGeo,  you have to have the phone aligned so that its long axis lies along the direction of steepest slope, in order to get an accurate measurement. The app really needs to be set up so that it will automatically determine the direction and magnitude of steepest slope automatically, regardless of which way the phone is laid on the surface; that would not only improve accuracy, but speed up measurement time. I’ll monitor the app to see if this is implemented.

Final thoughts: I started out biased towards Rocklogger because its evaluation version allows data recording and export; you need eGeo Compass’s registered version to enable that. I do like the additional recording options, and multiple data inputs, especially the customizable dropdown. And unlike eGeo, you have the option to record the true direction, not just magnetic. But Rocklogger’s requirement that you have the phone oriented along the direction of steepest slope is a dealbreaker for me; it reduces accuracy, and slows down the overall recording time. If this were fixed, I’d give the edge to Rocklogger; but as is, eGeo Compass is currently the better app.

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