Laser rangefinders and ArcGIS combined with three-dimensional photorealistic modeling for mapping outcrops in the Slick Hills, Oklahoma

Mohammed Alfarhan,Lionel White,Carlos Aiken,Dean Tuck

doi:10.1130/ges00130.1

Abstract

The mapping of geology is conventionally done visually in a hands-on fashion, and the data are recorded in a field book or with photography. An alternative technique that combines reflectorless laser rangefinders or high-speed terrestrial laser scanners, global positioning system, and the Environmental Systems Research Institute (ESRI) ArcGIS software platform has been developed that is effective for mapping geology at a distance and in three dimensions. Portable handheld reflectorless lasers are used to capture geologic features such as contacts and terrain and can be combined with digital elevation models in ArcGIS software. Fast terrestrial laser scanners capture an entire exposure at the detail and accuracy of (3D) photorealistic (virtual) models with the additional color information from image pixels. This latter method is expensive and complicated and requires significant amounts of field and processing effort. The laser gun approach is simple, portable, and cost effective. When integrated with ESRI ArcGIS software and a module, such as our recently developed ArcGIS extension 3DLT (laser tool), a simple yet sophisticated platform exists for mapping, visualizing, and analyzing outcrops in real time in the field. The potential of laser mapping is demonstrated in the Paleozoic outcrops of a structural geology teaching site in the Slick Hills, Oklahoma. Fast laser scanning and digital photography are used to build a 3D photorealistic model of an area of the anticline. The 3DLT is used for mapping specific detailed features such as contacts and faults. Three-dimensional quantitative information can be extracted from the geology with these methods. A laser rangefinder combined with 3DLT can image and display terrain and outcrop features in the field, in real time. Mapping with fast scanners requires several steps in processing of the point cloud data utilizing a variety of sophisticated and expensive software, but can capture an entire outcrop, such as a mountainside. The resulting model then can be analyzed in the lab. When combined with digital photography, virtual photorealistic models derived from point clouds can be even more effectively analyzed. The most appropriate method for digitally mapping geology depends on a variety of issues, such as cost, time, complexity, portability, and the project goals.

Highlights

Common methods for digital geologic mapping have included aerial photography, global positioning system (GPS), and the utilization of conventional laser and/or optical based surveying tools
Methods used for generating 3D photorealistic models have been developed at University of Texas at Dallas (UTD) using a series of nonlinear transformations to relate features in the real world of XYZ to the pixels on a photograph in UV space
With either a rangefinder in the field or with a cursor on a 3D photorealistic mesh model in the lab, which linear feature should be digitized in order to define the contact? For example, is ing)

Summary

Introduction

Common methods for digital geologic mapping have included aerial photography, global positioning system (GPS), and the utilization of conventional laser and/or optical based surveying tools. Digital geologic mapping of outcrops has been carried out with various combinations of GPS, cameras, high-speed laser scanners, and survey instruments (Xu et al, 2001; McCaffrey et al, 2005; Thurmond et al, 2005; Bellian et al, 2005; Pringle et al, 2006; Oldow et al, 2006). Terrestrial laser scanners (TLS) programmed to run at high speed (thousands to hundreds of thousands of points per second) generate dense point clouds (millions of points) at angle and range accuracies better than the handheld rangefinders. These scanners have been used to map geology, creating three-dimensional (3D) models that capture entire mountainsides (Thurmond et al, 2005; Bellian et al, 2005)

Methods

Conclusion