Proceedings International Workshop on Mobile Mapping Technology

li, rongxing

Bibliographic data

Monograph

Persistent identifier:: 856671290

Author:: Li, Rongxing

Title:: Proceedings International Workshop on Mobile Mapping Technology

Sub title:: April 21 - 23, 1999, Bangkok, Thailand

Scope:: 1 Online-Ressource (Getr. Zählung [ca. 400 Seiten])

Year of publication:: 1999

Place of publication:: London

Publisher of the original:: RICS Books

Identifier (digital):: 856671290

Illustration:: Illustrationen, Diagramme, Karten

Language:: English

Usage licence:: Attribution 4.0 International (CC BY 4.0)

Publisher of the digital copy:: Technische Informationsbibliothek Hannover

Place of publication of the digital copy:: Hannover

Year of publication of the original:: 2016

Document type:: Monograph

Collection:: Earth sciences

Chapter

Title:: [Session 6A: Applications (2)]

Document type:: Monograph

Structure type:: Chapter

Chapter

Title:: IMPROVED DEM EXTRACTION TECHNIQUES - COMBINING LIDAR DATA WITH DIRECT DIGITAL GPS/INS ORIENTED IMAGERY. Charles K. Toth and Dorota A. Grejner-Brzezinska.

Document type:: Monograph

Structure type:: Chapter

6A-4-2 achieved by using iteratively rectified images; it serves as a natural starting point in our investigation on integrating stereo imagery and LIDAR data for surface extraction. The Center for Mapping has been a pioneer in developing modern mapping technologies. The most recent mobile mapping system developed by the Center is the Airborne Integrated Mapping System (AIMS™) - a tightly coupled GSP/INS integrated positioning system supporting primarily digital sensor-based image data collection (Grejner-Brzezinska et. al. 1998). The prototype system currently employs a 4K by 4K imaging sensor (Toth 1998), and recently, test flights were combined with a LIDAR sensor. Based on the initial experiences, the sample data from these flights illustrate the implications of integrating laser range data with stereo-imagery and provide an early insight into future multisensor fusion- based surface extraction techniques. 2. SURFACE EXTRACTION METHODS Past surface extraction techniques have evolved around the use of predominantly analog film-based aerial photography. The usually large-format aerial camera- recorded films have been scanned at various resolutions, ranging from 30 to 5 microns, resulting in image sizes from 10K by 10K up to 30K by 30K. The radiometric representation is generally on 8 bits, or 3 x 8 bits for color; however, the effective resolution is typically not more than 6-7 bits. The large image sizes posed almost unmanageable difficulties for the early systems (which were unable to handle several hundreds of Mbytes of data). Apart from memory and disk limitations, the rather modest processing power was the main obstacle in developing surface extraction systems on general-purpose computers. Therefore, the first systems built by military mapping specialists (Helava 1989) were based on hardware implementations and were ultimately limited to perform only simple image correlations. With rapidly advancing generic computer hardware and software technologies, the implications of the inadequate computer processing power have completely disappeared by now. From an algorithmic point of view, existing surface extraction techniques have gone far beyond simple image correlation, although that function is still an integral part of the methods. Current systems can usually handle only fully oriented stereo pairs with monochrome image data. To minimize the number of operations, the massive amount of image data is handled at various resolutions. Forming an image pyramid, the matching procedure usually starts at a coarse resolution, typically at 512 by 512, and then by establishing an approximate registration, the search space is gradually narrowed down as the processing moves to the next higher resolution level of the pyramid. By tracing down the conjugate image primitives from the coarsest to the highest resolution, not only are the computational savings enormous, but also this scale- space approach makes the whole procedure reasonably robust. There is diversity among the leading techniques concerning the choice of the image primitives used to find conjugate elements in the images. Typical image features (primitives) are points, edges and regions, and a variety of interest points and edge extraction operators are also available with numerous segmentation techniques. Once the image features are matched at the highest level of resolution, an area correlation or a least squares matching is performed to refine the conjugate image locations. The performance of existing surface extraction techniques can be adequately measured since these systems have been widely used in production. Although different systems may deliver very different results for identical image data sets, some generic conclusions can be drawn (Gruen 1998). For smooth, rolling terrain at small and medium scale performance is usually good. However, it decreases rapidly for more complex scenes and with a larger scale, such as steep terrain, lush vegetation and dense urban areas with a variety of man-made objects. A comprehensive review of the large variety of surface extraction techniques is beyond the scope of this paper. Instead, recent relevant trends impacting the surface extraction process are listed here. Direct GPS/INS Orientation Data. The availability of exterior orientation parameters has always been assumed, since such parameters are the primary tool to provide the basic object space constraining for the matching process. However, in many cases, the orientation data determination process itself provides a large number of surface points, for example, automated relative orientation or automated aerial- triangulation. Then these object points can be used as seed points for the consecutive surface extraction procedure. With the recent development and widening use of GPS/INS-based direct orientation systems (Schwarz 1995; Grejner-Brzezinska 1997), points are no longer available for such purposes. Epipolar Geometry. The use of epipolar geometry provides a computationally efficient technique to reduce the otherwise two-dimensional search space into a more manageable one-dimensional matching problem. Obviously, confining the search space to a line may severely impact the robustness of the matching process. Inspired by the somewhat modest accuracy of the early experimental GPS/INS positioning systems, techniques have been developed to perform 1.5-D matching along epipolar bands. Direct Digital Imagery. Recent rapid technological developments have finally reached the imaging sensor - the last bastion of analog mapping techniques. CCD- based sensors have long been used in space and on the ground, but now they have started to penetrate the airborne surveying market. Since the size of the focal- plane CCD arrays currently falls short of the large- format aerial film dimensions, CCD frame sensors produce rather small footprints to maintain the

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