Abstract: CAD, DTM and GIS Tools for Mapping, Modeling and Analysis of Geologic Data: Coastal Erosion and Satellite Tracking of El Nino

Peter J. R. Buttner

Geology is the study of the rate and scale of change; for depiction and analysis, the products of change are represented by geologists as data on maps. These data take the form of points (e.g. coastline survey stations), lines (e.g. formation contacts or high tide lines) and polygons (e.g. areal distribution of a coastal barrier bar system). Software that provides assistance with the assembly, management, analysis and display of such spatially-distributed, three-dimensional geographic data has been developed for desktop microcomputers. Geographic-base and feature-attribute data used in geological studies are derived from two man types of compilations: raster or bit-mapped images produced by electronically scanning paper maps and photographs; and, vector images generated b electronically digitizing maps and various aspects of photographs Unlike the vector data, raster images are scale limited and restricted to narrow ranges of magnification. A common attribute of these desktop software tools is the ability to represent spatially-distributed data as vectors within a Computer-Assisted-Drawing or "CAD" framework. To some degree each of these software tools (e.g. ARC/INFO^TM and Auto CAD^TM) provide the mathematical procedures for defining the relationships between the point, line and polygons of a spatially-distributed geological data set. These relationships identify the topology of the data set.

One group of CAD software called geographic information systems, or GIS, provides a specialized setting for the organization of logical collections of spatial, image and tabular information on geographical features (e.g. geometry of barrier components) into geological themes (e.g. morphology and dynamics of a barrier island). Several types o GIS software are available: "stand-alone" (e.g. ARC/INFO^TM, PC ARC/INFO^TM, MapInfo^TM and ArcView^TM); "add-in" (e.g. ArcCAD^TM and LANDMARK^TM; both are "added-in" to AutoCAD^TM); and, "hybrid "packages that provide analytical preparation of data set for use in GIS (SOFTDESK^TM and EasySurf^TM DTM's that run inside AutoCAD^TM; CAD Overlay ESP ^TM raster to vector software that also runs inside AutoCAD^TM; MapExpert^TM which will export TIGER-based maps; SURFER^TM DTM which will "talk" to EasySurf^TM and AutoCAD^TM; and, CorelDRAW^TM and Micrografx Designer which will condition TIFF files for GIS registration).

Adoption of these tools for geologic studies is, in many cases, difficult, costly and time-consuming. To the initial co of the programs must be added periodic software maintenance and training expenses together with the cost of a well-endowed computer workstation. The learning curve for any reasonable stand-alone GIS is steep and long but the results are usually rewarding, enlightening and beyond expectation.

AAPG Search and Discovery Article #90954©1995 AAPG Eastern Section, Schenectady, New York