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Archive for the 'geology' Category

Map Point Slopes And Directions With Rocklogger

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.

Steepest Slope And Its Direction With eGEO Compass

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


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

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.

Final thoughts:

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.

Locational Soil And Vegetation Data In Android With SoilWeb

Application Name: SoilWeb

Description: Pulls up NRCS-NCSS soil, geology and vegetation data for a location.

Publisher’s website: SoilWeb

Cost: Free

Version/date reviewed: v.1.1  /  9-21-10

Phone/OS: Droid X / Android 2.1


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

If someone asked me to demonstrate apps that showed the true potential of Android-based portable geography tools, SoilWeb would be one of my top examples. SoilWeb queries US government soil survey data based on a GPS-derived location, then displays it on your Android’s screen. The intro screen gives basic instructions, as well as an example of the kind of data it will retrieve (Figure 1):


Tap on “Get My Location” to start up the GPS, and determine the coordinates for which data will be retrieved. Since the app only allows 30 seconds for position acquisition, it’s probably a good idea to run some other GPS app beforehand to “warm up” the system. Ironically, my house is in one of the few areas in the country with no data coverage; the app will tell me that, as well as bringing up a link to a US data coverage map (Figure 2):


However, I was in an area of New Mexico last week that does have data, and was able to fully exercise the app. After getting my location, the app retrieved two soil columns for the area I was in (Figure 3):


Tapping on the link at the top of the column brings up a description of it (Figure 4):


Tapping on the soil column itself brings up tabular data for both the soil, and vegetation types typical for that soil type and the climate of the area (Figure 5):


Awesome stuff, and I hope to see more apps like this in the future. I hope to try and bang out a few myself, but am unlikely to make one as good as this one. Kudos to Dylan Beaudette of the California Soil Resource Lab for putting this app together, and making it freely available.