Book Review: Airborne and Terrestrial Laser Scanning
Professional Surveyor Magazine - February 2011
George A. Maalouli
Laser scanning technology has matured and developed in the past two decades to become a leading surveying technology for the acquisition of spatial information. A wide variety of instruments with various capabilities are now commercially available. The high-quality data produced by laser scanners are now used in many of surveying’s specialty fields, including topographic, environmental, and industrial. These data include raw, processed, and edited dense point clouds; digital terrain and surface models; 3D city models; railroad and power line models; and 3D documentation of cultural and historical landmarks.
This book complements information already available in published textbooks and from online sources describing the general concepts and applications of laser scanners. The sections logically flow from describing basic principles to explaining data extraction and manipulation to discussing applications in various geospatial fields. Researchers and interested readers will appreciate the ample references at the end of each chapter.
The contents are fairly technical but neither complex nor confusing, and they can serve as a good reference for under- and post-graduate students. The book is also informative and helpful for practitioners who work with laser scanners to provide products and services.
Airborne and Terrestrial Laser Scanning is organized into nine chapters grouped into three distinct topics. The first is a detailed description of principals of laser scanners, light-measuring methods, components and properties of a laser scanner, operational considerations, data handling and storage, and system geometry and calibration. The second topic describes existing filtering and algorithms used for the data extraction, classification, and manipulation to generate client-specific products such as DEMs, building footprints, and the like. The final topic touches on applications currently using laser scanners.
Chapter 1 contains good information for specialists and non-specialists alike, defining the basic concept of light measurement and measuring techniques. It differentiates between 1) the time-estimation time-of-flight and phase measurement methods widely used by mid- to long-range scanners and 2) the “triangulation” method that is based on distances and angles and uses known baselines between the light source and observation point.
Also defined are the integrated components that make the system work. They include the scanner assembly, airborne GPS antenna and receiver (ABGPS), inertial measurement unit (IMU), control computer and recording units, and flight management system. Operational considerations are briefly discussed, while bathymetry and terrestrial scanning are also mentioned in a cursory manner.
In the next chapter existing methods and algorithms to convert and visualize collected point-cloud data are discussed. In most cases, it is necessary to convert from dense, true 3D multiple scans to a more manageable and visually appealing format such as raster elevation grids, which can be visualized as grey or color-based shaded images.
The authors mention intensity images created by recording the amplitude of the reflected laser pulse, but with few details. Point-based visualization is usually boring and requires some form of point exaggeration for better visual interpretation, such as the splatting method described by the authors. Various data structures are discussed, including the simple standard image raster, Delaunay triangulation, K-D tree, and Octree. For better point-cloud data interpretation, grouping of points that belong to some criterion is usually achieved through segmentation algorithms. The book describes most existing segmentation methods well, but they may be confusing to the non-specialist.
As a photogrammetrist, I enjoyed Chapter 3 because it closely relates to photogrammetric concepts. The authors define the geometric relation between the ground hit and the laser pulse as it leaves the sensor. The rotational elements, observation equations, and transformation models for laser scanners are well presented. Trajectory determination, systematic error sources, data artifacts, registration and calibration sections make easy and interesting reading but will be of more interest to the practitioners and researchers than the average non-specialist.
Chapter 4 is devoted to the data extraction, filtering, and modeling for both discrete and full-waveform sensor types. Detail is provided for filters such as morphological, progressive, surface-based, and segment-based. If the reader is interested in general performance of various filters, the filter comparison section highlights the findings of the ISPRS test, which studied eight different filters with airborne laser scanners of different characteristics.
Chapter 5 deals with current methods and algorithms for building footprint extraction from laser-scanner datasets. This long and detailed chapter describes the various current modeling methods including their strengths and weaknesses.
Chapters 6 to 8 provide a good reference for lidar applications. The first of those three chapters discusses forestry applications in the fields of forest inventory, forest management, carbon sink analysis, biodiversity characterization, and habitat analysis. The next deals with engineering applications in the field of 3D site reconstruction, structural monitoring, and corridor mapping. Chapter 8 then provides interesting examples of using laser scanning for the conservation and documentation of historical and archaeological sites around the world.
The book’s final chapter is devoted to a brief but informative description of mobile mapping and mobile systems. Highlighted modes of data collection include stop-and-go and on-the-fly. This chapter also summarizes system design for a mobile system. The discussion of railroad-track-based and road-based systems is thorough and informative.
In general, this book is a comprehensive collection of information from existing publications covering a large segment of laser scanner technology, ranging from basic concepts and system characteristics and components to various applications and techniques for data use, modeling, and storage. It can serve well as a basic text for laser-scanner specialists and practitioners, as well as under- and post-graduate students and as a solid reference for surveyors and other earth scientists.
About the Author
George A. MaalouliGeorge Maalouli, M.Sc. is vice president and chief technical officer of the Seattle division of Aero-Metric, Inc. He holds a M.Sc. in aerial surveying from the International Institute for Aerospace Survey and Earth Sciences in the Netherlands and has been actively involved in photogrammetry for 18 years.
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