Page 7 - i1052-5173-26-8
P. 7
Figure 3. Structure from Motion model of a mantle xenolith from Salt Lake (Āliamanu) Crater, Hawaii. Caldera marked in red. Verilith provided by Mike Bizimis.
©2015 Google Inc. Online version can be rotated, and is available at http://dx.doi.org/10.1130/GSATG257.S4.
reduce the 4 MB raw scan down to less than half a MB without GSA Today cover image(see http://dx.doi.org/10.1130/GSAT GSA TODAY | www.geosociety.org/gsatoday
losing any resolution on the cut surface. Peridotite mineralogy is G257.S3 for interactive online version). This is the best option for
easily identified by most students in the final model despite its viewing on mobile devices. By rotating lattice models with a
modest resolution. touchscreen swipe, students can see non-intuitive symmetry
elements, such as a cubic crystal’s three-fold axes, and the back-
The downloads include a KMZ model of Acasta Gneiss, the ground image adds context. The process of displaying interactive
oldest whole rock ever dated, at 4.03 Ga. Its verilith was loaned by COLLADA models in HTML 5 is far from self-evident, but this
Sam Bowring, MIT, and the model created with 123D Catch can paper’s sample file, using a 3D library from GitHub (2016), can be
be viewed in the source location in Northwest Territories by thou- downloaded and modified. Readers can simply search for “files/
sands of people who will never go there in person. Instructors can halite.dae,” and replace that URL with another file of their choice.
use these and other models that are shared by colleagues in
SketchUp’s 3D Warehouse (2016), the 123D Catch Gallery (2016), VIEWING VIRTUAL SPECIMENS IN WEB BROWSERS
SketchFab (2016), Thingiverse (2016), and other digital reposito-
ries. For example, the author downloaded fossil models from Manipulating virtual rocks using the Google Earth desktop
Brain (2016), processed them in MeshLab, and geolocated them in application is tedious due to the limitations of KML, an
Google Earth. Figure 4 shows a virtual ammonite from XML-based scripting language that has changed little in a decade
Semington, Wiltshire, England, and the downloads include a and lacks basic programming features such as do-loops. Google
model of Gryphaea arcuate from Hock Cliff, England. Earth was available as a more versatile web browser plugin and
application program interface (API), but that has been deprecated
Sometimes, people may want to display interactive specimens effective December 2015. A plugin-free API is expected in the not-
not linked to a particular location—for example, when the loca- too-distant future; meanwhile, an alternative approach is to
tion is not known. There are three approaches: First, COLLADA convert models for viewing on the web-based Cesium virtual
models can be viewed with software such as Adobe PhotoShopTM globe (Cozzi and Ring, 2011) using the glTF file format. A glTF
or Apple PreviewTM. Second, Google Earth version 6.0 (or earlier) version of the Vredefort specimen may be viewed at GEODE
can be downloaded from a legacy software portal such as (2016) using the Chrome web browser (Chrome is the only
FileHippo (2016). In early versions of Google Earth, the Primary browser that currently handles models in Cesium flawlessly). See
Database could be selected and made transparent with a slider, the GSA Supplemental Data Repository (footnote 1) for technical
hiding the surface imagery. The accompanying KMZ downloads details. Viewing in a web browser has distinct advantages because
include a rotatable, zoomable apatite crystal in Google Earth v. models can be manipulated with several JavaScript controls, such
6.0. The third approach is to embed a COLLADA model directly as radio buttons, numeric text fields, and multiple horizontal and
in a web page as in the case of the halite crystal lattice in the
7
