FROM 3-D HYDROSTRATIGRAPHIC MODEL TO 3-D PRINTED AQUIFER MODEL

Three-dimensional (3-D) printing provides unique opportunities to transform conceptual or empirical models into digitally produced physical realizations. Here, we present a workflow for building a physical representation of a 3-D hydrostratigraphic model of the Mahomet aquifer using a computer-guided printing system. The Mahomet aquifer stretches from the Illinois River eastward to the Indiana State line, and supplies groundwater to nearly 1 million people.

The printing process began with determining the correct export file type that would allow grids of the hydrostratigraphy to be imported into the 3-D printing software. We found that GIS Triangulated Irregular Network (TIN) format was compatible with the STereoLithography (STL) format of the printer based on its triangular mesh grid structure. We then converted ArcGIS grids in TIN format to Virtual Reality Modeling Language (VRML) in WRL file using ESRI’s ArcScene™ software. The WRL files were next converted to STL files to construct a 3-D solid object models using the free software netfabb (http://www.netfabb.com) and Meshmixer (http://www.meshmixer.com).

Three processes were key to exporting the GIS data to WRL format and then finalizing it in STL format. First, 2-D grids were made to represent the top and bottom elevations of each unit. The grids were then converted to 2-D TIN files using ArcScene. The vertical exaggeration was set to best represent the gridded data with enough detail when projected in 3-D. ArcScene was used to export the 3-D TIN to WRL format for each stratigraphic surface. Second, the virtual reality models of all top and bottom surfaces in WRL format were converted to STL format with netfabb. This conversion was necessary to produce a 3-D solid object for each stratigraphic unit that would be ready for actual 3-D printing. Meshmixer was used in the final process to construct each stratigraphic unit by integrating the top and bottom surfaces.

Through testing, we found that printing the model in different orientations had a significant impact on the printed resolution, as well as the stability of the model during the printing process. The prototype 3-D model of the Mahomet aquifer was printed vertically with the east side aligned along the base of the printer. With 3-D printers, extremely realistic models can be produced quickly and cost efficiently.