Research paperTouchTerrain: A simple web-tool for creating 3D-printable topographic models
Introduction
Terrain has a profound influence on many Earth processes and human activities, such that a thorough understanding of it is vital to many geoscience and engineering disciplines. Despite this importance, the nature and scale of terrain often places it outside simple comprehension, which leads to difficulty in the classroom when students are asked to make qualitative and quantitative measurements using traditional topographic maps (Tversky, 2003, Taylor et al., 2004, Ishikawa and Kastens, 2005, Rapp et al., 2007). 3D-printed models can overcome this problem by putting data directly into the hands of students, educators, citizens, and stakeholders (Hasiuk, 2014, Hasiuk and Harding, 2016). The goal of the TouchTerrain project is to overcome the most technically challenging barriers to more widespread adoption in the classroom by providing a web application for easily generating 3D-printable terrain model files of any area on Earth.
Elevation data is widely available in digital elevation models (DEMs) derived from remote sensing techniques with meter-scale accuracy or better (Bellian et al., 2005). DEMs can be visualized in a variety of ways (Buckley et al., 2004; Mach and Petschek, 2007; Mitasova et al., 2012). Traditional 2D visualizations include contour lines, color sequences/ramps, and hillshading. To trained geoscientists, the spacing between the lines also suggest the slope, i.e., smaller gaps indicate a steeper hill; however, students often find it difficult to make the leap from reading a contour map to visualizing a terrain's 3D shape.
Visualizing terrain data in 3D leads to additional visualization techniques (Johnson et al., 2006, Mach and Petschek, 2007). 3D viewers, such as ESRI's ArcScene, and digital globes, such as Google Earth, combine visualization of terrain properties in 2D space with interactive viewpoint navigation to enable users to explore terrain data in ways that they cannot in the real world. However, it is still not clear for what use-cases 3D maps are best suited (Schobesberger and Patterson, 2007, Popelka and Brychtova, 2013). Augmented reality sandboxes allow students to move sand and witness the resulting effects on topographic maps digitally superimposed on the sand and updated in real-time (e.g., Woods et al., 2016).
The intuitive and material nature of 3D-printed terrain models give them advantages over 2D maps and 3D computer visualizations. Actions such as zooming and rotating are accomplished via hand positioning of the model, and surface details are easily discerned. The models can be directly annotated with pens and can help visually-impaired users to comprehend terrain (Wild et al., 2013). Although the use of 3D-printed terrain models as instructional material is still in its infancy, early research has shown that such models have value, either on their own, or in concert with 2D and 3D terrain visualization methods (Rule, 2011, Williams et al., 2013, Horowitz and Schultz, 2014, Hasiuk and Harding, 2016).
As the equipment, software, and material costs for printing 3D models have come down, the greatest cost lies in generating a 3D model file of the chosen area that reliably prints well on a specific type of 3D printer. The expertise and time required to do this, along with the specialized software which may be required, is a hurdle to widespread use of 3D terrain models. The TouchTerrain project aims to remove this barrier, empowering educators to use 3D-printed terrain models from any area on the Earth as a basis for novel teaching methods in the classroom and the field.
Section snippets
3D printers
A 3D printer is designed to take information from any digital 3D model and make a tangible 3D model (Pham and Gault, 1998). “Fused Filament Fabrication” (FFF) is one 3D printing method that uses plastic filament with a small circular cross-section (often 1.75 mm or 3 mm in diameter). The filament is heated to a semi-molten state and then extruded through a nozzle with an orifice smaller than the original filament diameter (e.g., 0.4 mm). After the filament is added to a model, it quickly cools
TouchTerrain architecture and Google Earth Engine
TouchTerrain has a client-server architecture (Fig. 3). The server is written in Python and, in conjunction with Google Earth Engine (GEE), performs heavy computations that would not be feasible to run on the frontend, in the client's browser. The client is a webpage written with JavaScript which communicates with both the server and GEE.
We use Google Earth Engine (GEE) to access and process a variety of DEM rasters. Unrelated to Google Earth, Google Earth Engine is a development environment
Conclusions
We explored creating of digital 3D terrain models suitable for 3D printing on personal 3D printers. After initially hand-crafting the digital models via a complex, manual workflow utilizing several software tools, we created a web-application that hides much of the complexity from the end-user. As result, the user receives 3D-printable, multi-tiled model files that cover the requested area.
The TouchTerrain server can be used at http://touchterrain.geol.iastate.edu. Open-source code can be
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