CONSTRUCTING GEOLOGIC CROSS-SECTIONS, FENCE DIAGRAMS AND BLOCK DIAGRAMS WITH CAD/GIS APPLICATIONS

The visualization of stratigraphic and structural relationships is often best accomplished through geologic cross-sections, fence diagrams, and block diagrams. Traditionally these diagrams are constructed during courses in stratigraphy, structural geology and field geology. Unfortunately, many aspects of constructing these types of diagrams are relatively tedious and time-consuming. Current CAD/GIS software applications, such as AutoCAD Map, Surfer, and ArcGIS, provide the necessary tools and environment that can dramatically lessen the time taken to construct these types of diagrams.

User-defined coordinate systems (UCS) are the key to rapidly constructing geologic cross-sections from geologic base maps. Markers are inserted into the base map along the line of the cross-section where contacts and/or contour lines of interest cross. The markers are “snapped” to the cross-section line, however, the elevation is entered interactively so the user can match the elevation. One end of the cross-section line is designated as the UCS origin, the other end as the positive x axis, and the z axis of the world coordinate system is designated as the positive y axis. This UCS system contains the plane of the cross-section with the inserted markers forming the topographic profile. The remainder of the cross-section is sketched as if it were a typical geologic map.

Fence diagram and block diagrams are constructed in a similar fashion except that custom application programs and/or scripts are utilized to automate the input of subsurface data. CAD may be used to view the fence or block diagram from virtually any perspective. With ArcGIS 3D analyst the fence or block diagram surfaces may be assigned any level of transparency in order to visualize the overall structure. Block diagrams may also be “cut”and viewed from any perspective point.