GIS Programming - Participation Assignment #2

This assignment was to find and summarize a technical/professional article relating to Python or GIS. The article I am reporting on is:

Visualizing structural geology: From Excel to Google Earth

T.G. Blenkinsop, 2012: Computers and Geosciences v. 45, pp. 52 – 56.

Link to article introduction at DeepDyve.com

This article is of particular interest to me for my work in structural geology and minerals exploration and especially for small companies like the one I work for, which may not have access to expensive GIS software like ArcGIS.  This system uses a virtual globe, specifically Google Earth Pro, and Excel enabled for macros.  (Google Earth Pro used to cost, but now it’s free.)

   The ability to visualize geologic elements in 3D is essential for structural analysis of the Earth’s crust.  An understanding of the deformational and tectonic history of regions and even continents is mad possible when the various planar and linear structures are brought together and their spatial relationships examined.   Measurements done in the field are normally entered into an Excel spreadsheet, with spatial coordinates and/or latitude and longitude, as well as measurements of the orientations of elements such as the limbs and axes of folds, lineation, cleavage and stratigraphic bedding.  The orientations are expressed in terms of the azimuth of a plane’s slope or a line’s direction of plunge, and the degree a linear feature’s plunge or the dip (slope) of a planar feature.  Relationships between various elements’ orientations can help determine how many generations of deformation an area has experienced, and in what order. 

The author has combined a library of 3D symbols such as rods and flat prisms of various shapes and colors, with an Excel workbook called 52K .  The Excel macro uses Visual Basic for Applications to convert field data measurements of the structural elements into a KML (Keyhole Markup Language) for Google Earth Pro.   Any field measurements recorded by hand in the past can be fairly easily entered into Excel spreadsheet form, incorporated into other structural data sets, and presented in a nicely intuitive form on top of a Google Earth landscape, viewed in the 3D mode.  This method also allows structural principles to be presented to students and novices of structural geology, to allow easier understanding of the 3D concepts involved. 

The authors present an example (pictured below) of how, by  measuring very small localized features in numerous locations across an area, general large trends can be represented alongside the Google Earth landscape and compared to other planar and linear features.  In the case of the author’s example, the consistent orientations of various types of structures indicate that the area was deformed in a single event.  This view also helps us to intuitively visualize structures which are not obvious from the field.

In this figure (from Blenkinsop’s 2012 article),  white planes are stratigraphic bedding and red planes are schistosity, or planar deformational parting of the rock fabric. The blue rods represent the hinge or bend of a fold.  The red rods represent the intersection between the two types of planes.