Virtual globes represent a paradigm shift for geoscience education. (…)
[they allow] to combine multiple 2-D images into one 3-D image with topography. Models viewed in Google Earth® are more intuitive for visualizing 3-D geological structures than traditional paper maps and cross-sections.
Google Earth® and other virtual globes have only been available for a decade, yet they represent a significant paradigm shift for geoscience education.
Virtual globes emerged at the close of the last millennium (Bailey 2000). Gore (1998) strongly endorsed this technology and predicted that vir- tual globes would revolutionize spatial visualization and data analysis for geo- science research and education.
Earth-Browser was the first working digital globe application to appear in 1998, followed by other ‘first generation’ vir- tual globes until 2004. Development of the XML-based markup language ‘Keyhole Markup Language’ (KML) by Keyhole Corporation in the early 2000s made virtual globes easily extensible. Google Earth® was released in 2005 as the newly named KML-based geo- browser (after Google Inc. purchased Keyhole Inc.). Google ensured the success of Google Earth® by releasing control of KML to the Open Geospa- tial Consortium in 2008, thereby estab- lishing KML as the standard for inter- active digital globes. KML is now the scripting language for all major virtual globes such as ESRI’s Arc Explorer, Bing Maps 3-D (formerly MSN Virtual Earth), Google Earth®, and NASA’s World Wind (Wilson et al. 2007, 2008; Wernecke 2009; Whitmeyer et al. 2010; De Paor et al. 2010; De Paor and Whitmeyer 2011).
Novice students and non- professionals typically experience diffi- culties when attempting to visualize 3- D geological structures with paper geo- logic maps and cross-sections (Piburn et al. 2002; Kastens and Ishikawa 2006). As emphasized by Whitmeyer et al. (2010), interactive geological maps in Google Earth® communicate 3-D geological data more intuitively than the traditional format of separate
paper maps and cross-sections. Drap- ing geological maps over topography combined with creating emergent cross-sections permits students to remove much of the cognitive barrier involved in trying to piece together 2- D paper maps and paper cross- sections.
The main purpose of this paper is to highlight the practical and accessible nature of Google Earth® when combined with SketchUp, COLLADA, and WxAzy- gy®, and the ability to create engaging 3-D interactive models from geological maps and cross-sections constructed by students or professionals.
Thompson used an early version of the Grotto Creek model to create a Youtube video (Thompson 2011) illus- trating the difference between the >3 km apparent map thickness of the green Palliser Formation limestone and the ~250 m true thickness observed in the cross-sections (Fig. 5A, B). This illustrates one powerful capacity for these Google Earth® models for edu- cation purposes.
This Grotto Creek Google Earth® model will be used in intro- ductory geology courses to illustrate the ‘rule of Vs’ and why inclined con- tacts are not always straight lines. The terrain overlay combined with the topography in Google Earth® greatly enhances what may be difficult for some students to visualize with only the topographic contours on topo- graphic maps.
Thompson’s Youtube video (Thompson 2011) will be used in the introductory field school, and structural geology courses to graphical- ly illustrate the difference between true and apparent thickness. The vertical and horizontal sliders will be used in these courses to illustrate how folds and faults can develop and how to construct proper cross-sections. Both concepts can be troublesome for novice students.
pretation and are built into Google Maps but strangely not into Google Earth®. We devised four methods for adding contours to the Google Earth® terrain.
In the first method (Fig. 8A) a screen shot of the region of interest is taken in Google Maps with its terrain feature switched on. This is imported into Google Earth® as a ground over- lay and draped over the matching topography. This works well because Google Maps and Google Earth® share the same DEM (if a map from a different source were draped onto the Google Earth® terrain, the resultant contour lines might be far from hori- zontal). A disadvantage of this method is that paths or polygons drawn with Google Earth® tools will be covered by the ground overlay image (paths and polygons cannot be given a higher KML draw order). However, if the transparency of the image is adjusted, map features beneath become visible. This approach is the fastest and it pro- duces acceptable visual results if the region of interest is not too large – on the order of 10 km2 – otherwise, the contours become too dense and the
image file becomes very large.
The second method (Fig. 8B)
involves manually tracing the contours using the Google Earth® ‘Add Path’ tool. Here, the first step is to create a rectangular polygon similar in size to the region of interest. When the alti- tude mode of this rectangle is set to ‘absolute’ (the height is 1800 m in Fig. 8B) the contact with topography can be seen (indicated with the white bold line) and traced out by hand. This process is then repeated for all the desired altitudes.
For the third method, the DEM from Google Earth® is import- ed into SketchUp using its ‘Get Cur- rent View’ tool (Fig. 8C). Once the DEM is imported, by intersecting it with a set of equally spaced horizontal planes, contours can be produced and exported back into Google Earth® as a 3-D model. Two disadvantages of
this approach include the limit of ~4 km2 for the area that can be imported and the large file size.
The fourth method (Fig. 8D) is a derivative of the second method. Instead of tracing the intersection of the rectangular polygons with the DEM, the rectangles are made 90% transparent (10% opaque) and stacked by copying them while increasing their altitudes. Then a solid colour base rec- tangle is clamped to the ground under this stack. Here the base colour is blue and the altitude ascends from blue toward white because the base layer is covered with more rectangular planes at each elevation. This method can be completed fairly quickly and can extend over large regions (subject to the effect of Earth’s curvature).
The above discussion demonstrates the potential for Google Earth® to be used for visualizing complex geologic structures and processes. Additional steps can be taken to show under- ground geologic structures in situ (meaning in their original locations) as shown in Figure 9. These KML objects were created using image processing tools to 1) capture a surface image tile, and 2) remove sections of that tile which would obstruct the user’s view of the cross-sections. In version 5 of the Google Earth® desktop applica- tion, surface tiles are made transparent by highlighting ‘Primary Database’ in the Layers sidebar and then moving the transparency slider all the way to the left (see ‘A’ in Figure 10). In Google Earth® version 6.2, the pri- mary database is always opaque; instead the Radar item in the Weather Layer must be made transparent. The cut-away tile is reinserted as a ground overlay and is draped on the terrain. An obvious next step would use the line drawn along the surface (the yel- low line in Fig. 9) to define the cross- section(s) and perform the surface image tile cut-away. The image tile cut is also a split, where the two resulting sections of the ground overlay can be used to view the cross-sections in situ from opposing directions.
The ultimate goal for future Google Earth® models expanding upon the Grotto Creek model presented here is to create a series of 3-D interactive VFTs through the Canadian Cordillera. As mentioned by Whitmeyer et al. (2010), these interactive Google Earth® geological maps are more intu- itive for non-professionals than tradi- tional paper maps and cross-sections. It is also hoped that VFTs employed as a supplemental introduction to real field experiences will greatly decrease the overwhelming nature of first field experiences (as summarized in Mogk, 2011). In the future, this pilot Google Earth® model will be expanded to include the extensive mapping and structural analysis outlined by Clark (1949), Balley et al. (1966), Price (1970), Dahlstrom (1970), Price and Mountjoy (1970), Monger and Price (1979), Price (1994), McMechan (1995), and Simony in Spratt et al. (1995).
Google Earth® and SketchUp were used because they are well inte- grated with each other, supported by multiple platforms, relatively simple to use, widely available, and free. For
most geosciences tasks, SketchUp is sufficiently powerful; however it can- not wrap a texture around a sphere or draw a line on a curved surface. There are free Ruby plug-ins available for SketchUp that enable these tasks. Other software is available that could create similar models to the one pre- sented here, such as Gplates from Earthbyte, Layerscape from Microsoft, Move software from Midland Valley, NASA World Wind, GEON, Open Topography, etc. SketchUp was used because the others are either not free, not cross platform, or have a steep learning curve. However, with the sale of SketchUp to Trimble Navigation Inc., the future of free SketchUp is unclear.
Google Earth® APIs. Once again, these were used because they are well integrated, supported by multiple plat- forms, relatively simple to use, widely available, and free. While there are many other possibilities for creating 3-D models such as LightWave 3-D, Maya, 3ds Max, many of these are heavy weight modelling applications with steep learning curves that would be underused for geoscience model- ling.
Finally, Google Earth® Layers were adjusted and manipulated using WxAzygy® to create a queryable ’cut- away’ transparent view of in situ geolo- gy. One powerful application of WxAzygy® is that it provides a con- venient platform for creating COLLA- DA and KML directly in Google Earth®. Unfortunately, Google Earth® recently announced that it will no longer support the GE COM API, which makes the creation of transpar- ent tiles much more difficult.
Google Earth® and other virtual globes present excellent media for analysis of surface data such as geolog- ical maps draped over topography.
The addition of Google Earth® API, KML, and COLLADA has greatly enhanced the 3-D visualization capaci- ty for Google Earth® models. COL- LADA models retain azimuthal orien- tations (unlike placemark icons), while KML permits users to add custom data in a variety of formats, and the Google
Another significant application for Google Earth® models is the abili- ty to immediately ‘fly and explore’ fea- tures embedded within the text of papers such as this. Regardless of the potential for assisting students in acquiring the necessary spatial cogni- tive skills during their voyage from novice student to professional geolo- gist, most people are engaged by this incredible technology.
Further Google Earth® appli- cations introduced here include the use of vertical sliders to create emergent cross-sections capable of sliding through topography, horizontal sliders that reconstruct a structural recon- struction model, and queryable ‘cut- away’ cross-sections embedded into topography.
Virtual globe programs allow for integrating multiple two-dimensional (2-D) images into one three-dimensional (3-D) image with topography. Immediately after their their emergence in the late 1990s, they were recognised as a technology that would reshape spatial visualisation and analysis of data in the geoscience research an education fields (Gore, 1998 in Boggs, et al., 2012).
The first working digital globe application was the Earth-browser, released in 1998. It was followed by the first generation virtual globes, which were made