3-D Modeling Workflow of McHenry County, Illinois
The ISGS has also been using a suite of software packages to develop a workflow aimed at 3-D geologic mapping from raw data to a final product. Key to this workflow is the ability to visualize and interpret geologic data in the 3-D environment, which at this point, has been achieved using custom tools in ArcGIS. These tools simply integrate the built-in toolsets in ArcGIS, but they allow for rapid 3-D visualization of attributes associated with the data (e.g. lithology, color, stratigraphy, downhole geophysical logs, combinations of attributes). Furthermore, these tools allow for “on the fly” geologic interpretation in the 3-D environment such as water-well record “picks” and interpolation of geologic contacts. In McHenry County, using these tools, more than 11,000 stratigraphic interpretations have been made in the water-well records since the start of the project (2008).
(Left) Regional 3D Geologic Surfaces created in ArcGIS. (Right) 3D Visualization of data in ArcGIS.
However, as versatile and efficient as these tools are, inherent limitations within ArcGIS constrain their application to 3-D geologic mapping. For example, the efficiency and stability of ArcGIS are dependent upon the RAM capabilities of the workstation. Detailed land surface models (e.g. LIDAR), large borehole datasets and other 3-D visual datasets (cross sections, downhole geophysics) can significantly limit processing efficiency. Therefore, a second software package, Geovisionary, has been used as a supplemental 3-D visualization tool. Geovisionary is capable of displaying high resolution datasets (e.g. LiDAR, aerial photography) in full resolution in a 3-D visualization environment along with other subsurface geologic data (well records, geophysical profiles). For example, these visualization capabilities have allowed for the highest resolution of geomorphic relationships to soil types/geology than ever before in McHenry County (e.g. lithologic facies within glacial outwash fans). However, the ability to build and record geologic interpretations in Geovisionary is limited to strictly digitization at land surface. Furthermore, subsurface digitizing functions in both ArcGIS and Geovisionary are extremely limited or absent.
Subsurface Visualization in Geovsionary
Building a 3-D GFM based on interpolation of individual 2-D surfaces is often painstakingly tedious and may often underrepresent the sedimentological nature of the geologic contacts (e.g. erosional scour relationships). Thus, GSI3D is also being incorporated into the workflow as a final model-building tool and client-user interface. GSI3D is a 3-D geologic mapping software package developed by Insight, GmbH and the British Geological Survey that constructs 3-D maps from cross sections and allows for versatile digitization in a stratigraphic context. Borehole interpretations and interpolated surfaces that are iteratively generated from ArcGIS and Geovisionary can be viewed in GSI3D and incorporated into interpretations, and the cross section-based approach allows the geologist to further incorporate sedimentological relationships between stratrigraphic units (e.g. erosional, depositional, etc). In McHenry County, 32 key cross sections, which incorporate the highest quality data drilling and geophysical data, were used as an initial framework for the 3-D model. Many additional sections have been included to further delineate geologic complexities at both county and local scales.
Fence diagram of cross-sections in GSI3D
GSI3D User interface