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Figure 1. Virtual rock created with SketchUp and geolocated at collection site, Rheems Quarry, Pennsylvania, USA. Online version can be rotated, and is available
at http://dx.doi.org/10.1130/GSATG257.S1. ©2016 Google Inc. Image: Landsat. Inset: Photographing hand specimen at arm’s length. Background is irrelevant as
it will be cropped.
images in a KMZ archive. COLLADA (Arnaud and Barnes, 2006)
is the format used to display 3D buildings, bridges, etc., on the
Google Earth terrain, but De Paor and Piñan-Llamas (2006) and
De Paor and Williams (2006) discovered that they could create
much larger crustal models that can be made to emerge from the
subsurface (De Paor, 2007) with a slider control (see also Chen et
al., 2008; De Paor and Whitmeyer, 2011; Blenkinsop, 2012; Boggs
et al., 2012; Karabinos, 2013; St. John, 2014).
Slab-Shaped COLLADA Models
Consider a rock, which we here define as the verilith (Latin for
“real rock”) with two parallel sides and minor thickness, such as
slate, shale, flagstone, or any hand specimen sliced thinly by a
rock saw. Figure 1 shows a sample collected from a limestone
quarry near Rheems, Pennsylvania, USA (De Paor et al., 1991; De
Paor, 2009). Photographs of the flat sides were applied to a rectan- proof-of-concept by De Paor (2007) and implemented on a large
gular block in SketchUp (Fig. 1 inset) following the method of De
Paor and Piñan-Llamas (2006; see also De Paor, 2007), and the
later rediscovery of the method by Van Noten (2016). Model
construction is explained in detail in the GSA Supplemental Data
Repository (see footnote 1), but the process can be summarized as
the digital equivalent of gluing photographs to plywood and
cutting object outlines with a jigsaw. The Rheems model was
exported to Google Earth and placed at its collection site. A KML
file was scripted to make the specimen rotate about a vertical axis
in response to the Google Earth slider. (The COLLADA models in
the online versions of all figures respond to mouse drags or touch
swipes—see the GSA Supplemental Data Repository [footnote 1]).
In lab class, students can clearly see that the limestone bridges
crossing calcite veins are not identical in shape on either side of GSA TODAY | www.geosociety.org/gsatoday
the specimen, and they are challenged to visualize the complex 3D
forms in the specimen’s interior, which was the purpose of the
exercise in this case.
Ovoid- and Hemi-Cylinder–Shaped COLLADA Models
A similar approach was taken with ellipsoidal, or ovoid, and
hemi-cylindrical specimens, as illustrated by KMZ downloads
accompanying this paper. Six photographs were draped over a
model of an ovoidal beach pebble in the ± x, ± y, and ± z direc-
tions. To represent cut drill core, cylinders were extruded from
circles in SketchUp, then sliced longitudinally, with core photo-
graphs applied as textures. When imported into Google Earth,
such specimens can be made to rise out of the subsurface at their
drill site in response to the slider control. This was done as a
scale using Big Data IODP repositories by St. John (2014).
COMPLEX SPECIMENS AND 3D SCANNERS
It is possible to create complex models with SketchUp, but for
intricate specimen shapes, 3D scanning is less tedious. A relatively
inexpensive NextEngine (2016) scanner was used to model pseu-
dotachylite from Vredefort, South Africa—Earth’s oldest and
largest known impact structure (De Paor et al., 2010; Fig. 2). Rock
specimens had been collected during legacy graduate student
mapping by Simpson (1978) before the region became a protected
World Heritage Site. Specimens were retrieved from long-term
storage and scanned. Open-source software (MeshLab, 2016)
(zBrush is a sophisticated, albeit expensive alternative [Michael,
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