# 18 – Quick Review of GeoID and Digital Compass Clinometers


GeoID is a smart device app (available in iTunes, Google play, and CNET) which is a powerful tool for the field geologist, from student to experienced professional. It combines a variety of useful functions from a compass clinometer to plotting and analysis of 3D planes and poles. In this post I’m going to review some key features of the app, after having field tested it over two field trips in the North West Highlands of Scotland.

Background on the App


GeoID was developed by Jin Son, an independent developer and Energy Systems Engineering student based at Seoul National University. I’m not sure how long ago he developed the app, but it has to have been around more more than 12 months. It has not been rated at all in iTunes, and has had only a few ratings in Google’s App Store (4/5 stars).

Compass Clinometer Feature
There are already a range of apps out there that can effectively replace your traditional compass clinometer (e.g. GeoCompass, Strike and Dip), but none I have seen have the utility and design to match GeoID.

But the question to ask here is not which app looks better, but rather is a compass clinometer on your phone/tablet more accurate than a traditional compass-clino? Well the accuracy, and indeed precision, of the digital compass and digital clinometer is the product of two things: the hardware, and the coding. The compass part of the software uses both the in-built magnetometer AND the accelerometer. The magnetometer measures a heading from the Earth’s magnetic field, and combines this with data from the accelerometer on the orientation of the phone, to give you a direction of travel on your screen. Most compass applications on smart devices provide up-to-date corrections for magnetic vs. true north, so this shouldn’t be an issue with well coded apps. The general, better-informed, consensus in many online forums is that the accuracy of newer digital compasses is negligible compared with traditional needle compasses. This is based on direct comparisons between digital and analogue compasses reported online, and conducted by myself.

The clinometer seems to be more precise than analogue clinometers in most compass-clino’s. In a blog post I found, the iPhone’s clinometer was compared, by a carpenter, with a tilt box (a common, high precision clinometer used in many professional workshops). He wrote:

“Tried Clinometer last night and compared it to my tilt box, its most likely as accurate as the tiltbox – I used it as a reference to find out if two parts of a railing I am building were co-planar, the difference between the two planes was within 0.1 degrees between the tiltbox and the iphone app. On an absolute scale (i.e. I didn’t zero the reading on the first plane before moving it to the second plane), the two readings were within 0.1 degrees of each other, that’s probably as accurate as it gets in my shop.”

So it seems that the compass clinometer on a smartphone may well be a healthy rival to the conventional analogue device. Its power multiplied by the ease and speed with which it can make readings (which is not always a benefit, as I’ll discuss later).

GeoID further increases the power through clever coding. Dip/strike or Dip/Direction readings can be averaged over a given time interval to make readings more stable and precise. So when recording a surface there is small delay before a “stable” reading can be taken. If you record a reading before it is stable you are warned with a sound.


Data recording & real time plotting
So, the compass clinometer is a quick, accurate and powerful tool. On top of that, in GeoID the compass clinometer button allows you to quickly gather and record lots of structural data on poles and planes, all whilst seeing it plotted in real time onto a stereonet of your choice. Plus, if to have GPS in your device, each datapoint is geotagged!


I tested the app out on a thrust-related fold in Durness limestone on the shore of Loch Assynt, North West Highlands of Scotland. In under an hour I was able to collect 300 dip and dip-direction measurements. Although a really nice set of data, I noticed that the ability to gather such a large volume of data must be used with care. The limestone here is heavily carstified, and so measuring a large number of surfaces resulted in quite a large scatter on each of the fold limbs. Arguably, had GeoID an in-built averaging function this would have been less of a problem, but alas it was.

Once the data is collected, you can see the stereonet full-screen and change from equal-area to equal-angle projections. One thing that would be really useful here would be the ability to have layers of data so that planes may be fitted to each of the limbs to come up with a mean plane per limb, such that you could read off things such as the mean plunge and plunge direction.

I had also given my iPhone to another geologist to gather some extra data. Although smaller, it could be placed on a clipboard to average the bedding plane surfaces. The app allows you to then share the data via email, bluetooth, or export to file, however there is no ability to collaborate on the same project, so I was thus unable to amalgamate the two datasets.

I really like the GeoID app in its simplest form, as a tool for gathering dip/direction data quickly and accurately. I think that it has a lot of potential on the analytical side of things, although I appreciate the complexity in implementing such features into the program. What I think this app needs is more users, more rafters, and for us to give some constructive feedback to Jin Son on how he can make this app even more awesome!

– Compass clinometer is incredibly useful and accurate
– Ability to quickly gather and store pole/plane structural data
– Real-time plotting of data allows on-the-fly interpretation
– Very user friendly
– Easily send/export data

– Limited to one layer of data
– No structural analysis relevant to folding etc
– Cannot collaborate on, or amalgamate projects


One thought on “# 18 – Quick Review of GeoID and Digital Compass Clinometers

  1. Pingback: #19 Update: Should you trust your digital compass? | Darren Wilkinson

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