Emmanuel P. Baltsavias

A comparison between photogrammetry and laser scanning

A comparison between data acquisition and processing from passive optical sensors and airborne laser scanning is presented. A short overview and the major differences between the two technologies are outlined. Advantages and disadvantages with respect to various aspects are discussed, like sensors, platforms, flight planning, data acquisition conditions, imaging, object reflectance, automation, accuracy, flexibility and maturity, production time and costs. A more detailed comparison is presented with respect to DTM and DSM generation. Strengths of laser scanning with respect to certain applications are outlined. Although airborne laser scanning competes to a certain extent with photogrammetry and will replace it in certain cases, the two technologies are fairly complementary and their integration can lead to more accurate and complete products, and open up new areas of application.

3-D Building Reconstruction with ARUBA: A Qualitative and Quantitative Evaluation

Reliable and accurate 3-D reconstruction of man-made objects is essential for many applications using digital 3-D city models. Manual reconstruction of buildings from aerial images is time consuming and requires skilled personnel, hence large efforts are being directed towards the automation of building detection and reconstruction. In this paper we present ARUBA — a framework for automated 3-D building reconstruction. After highlighting our strategy and concisely describing the framework and its modules, we evaluate the reconstructed roofs relative to accurate reference data based on three criteria: completeness, geometric accuracy and shape similarity. Finally, we interpret the results of the performance evaluation and make suggestions for improvements.

Orthophoto generation using IKONOS imagery and high-resolution DEM: a case study on volcanic hazard monitoring of Nisyros Island (Greece)

Georeferenced high-resolution satellite images can be used for acquisition of topographic information, navigation and visualisation for various environmental studies. The present study is part of the multidisciplinary EU project GEOWARN related to monitoring, warning and emergency planning for volcanic hazards in the island of Nisyros, Greece. Here, the main aim was the orthorectification of a 1-m resolution pan-sharpened IKONOS Geo image of Nisyros island. For the orthorectification, a digital elevation model (DEM) with a cell size of 2 m and an RMS accuracy of ca. 3.5 m was used, as well as 38 selected ground control points (GCPs) measured with differential GPS. An object-to-pixel space transformation using the ground control points was computed using two different models, a relief-corrected affine transformation and the polynomial mapping functions of Kratky. These transformations were used for orthorectification and the orthophoto accuracy was evaluated using GCPs as check points. Postprocessing for radiometric improvement of the orthophotos was applied. The orthophoto and the DEM served as basic tools for subsequent base mapping and visualisation. D 2002 Elsevier Science B.V. All rights reserved.

Spatial decision support systems for the management of informal settlements

Abstract Informal settlements are characterized by rapid, unstructured expansion, poorly constructed buildings, and destruction of the local ecosystem. The improvement of living conditions in informal settlements is best tackled at the local level. Effective local planning and management, however, can only be made through access to adequate geo-spatial data. This paper considers a number of promising trends in the realm of spatial information and the contribution which each of these may make to greater capability, validity and accessibility in an Interactive Decision Environment (IDE) for urban planning and management. The potential development directions reported in this article offer increased capabilities for frequent data update, new directions for modeling and visualization, and wider data accessibility and dissemination. We examine the role of Geographic Information Systems (GIS) for managing living quality improvement in informal settlements. Data capture options are then explored with emphasis on the potential of imagery derived from low-cost digital aerial imagery. Developments towards automatically generating two- and three-dimensional settlement models from this imagery using remote sensing and digital image analysis techniques are outlined. We conclude with an examination of the integration of visualization technologies in IDE and their role in the dissemination of spatial (and other) information for urban planning.

Macro to Micro Archaeological Documentation: Building a 3D GIS Model for Jerash City and the Artemis Temple

Digital photogrammetry and geographic information system (GIS) techniques have a direct and major role for fast and accurate measurements to generate 3D object models and perform reverse engineering. Hence, these techniques can be favorably employed also for archaeological documentation and preservation. This work serves as a pilot project to illustrate the capabilities of such techniques and also aims at generating some expertise for a longer-term objective of a national project that can be carried out in cooperation with the Department of Antiquities, Jordan. The main objectives are threefold. The first one is to build a 3D virtual reality model of the Artemis Temple that will serve as an important documentation of the Temple. It was never documented as such before. The second one is to construct a GIS model of the Jerash City. Finally, the Artemis model will be incorporated in a 3D GIS model, which will conclude Phase I of this project. The documentation is in fact very important as all temple areas will be modeled with very accurate measurements and detailed texture, which can allow visualization, preservation and reconstruction of the temple.

Integration of ortho-images in GIS

Digital ortho-images provide great advantages in comparison to their analogue counterparts, especially with respect to flexibility, production of derived products, and combination with other data sets. Today, production of digital ortho-images has become more operational due to the development of more powerful computers with sufficient resources, easier acquisition of input data, increased generation of digital data, development of many commercial ortho-image production systems, and new application areas, particularly in connection to GIS and digital mapping. Different aspects of integration of ortho-images in GIS and the related requirements are addressed. The paper focusses on the different extensions and possible uses of ortho- images in a GIS. Today digital ortho-images are primarily used either for visualization or as a backdrop. However, ortho-images offer many, to a large extent unexploited possibilities, especially for the update of digital maps, automated mapping, and the generation of new data bases. Different modes for the extraction of 3-D information and object classification are presented. The paper concludes with an outline of future trends in research and development.

Geometric and radiometric performance evaluation of the Leica/Helava DSW200 photogrammetric film scanner

In this paper geometric and radiometric investigations performed with two Leica/Helava DSW200 scanners will be presented. Good quality test patterns and accurate processing methods for their performance evaluation have been employed. The geometric tests include global and local geometric errors, misregistration between color channels, geometric repeatability, and determination of the geometric resolution. Efforts were made to separate the contribution of various error sources (especially mechanical positioning, electronic errors and lens distortion) on the total error. The radiometric tests include investigation on noise, linearity, dynamic range, spatial, temporal and spectral variation of noise, and artifacts. After a brief description of the scanner, details on the above investigation, used analysis methods and achieved results will be presented. The most important errors, especially for organizations employing the scanner in production, are nonrepeatable geometric errors that are due to mechanical positioning inaccuracies and vibrations. This causes whole CCD image tiles (4 million pixels) to be systematically shifted with respect to their neighboring tiles, with obvious negative influence on any subsequent measuring task.

Trinocular vision for automatic and robust 3D determination of the trajectories of moving objects

An automatic procedure for tracking signalised points on multiple, differently moving surfaces will be described. The practical tests involve tracking of points on a person walking within a calibration frame. Three simultaneously acquiring CCD cameras, which are oriented using control points, provide the input data. For implementation, the hardware (H/W) and software (S/W) of a digital photogrammetric system have been used. The procedure includes extraction of the signalised points and finding corresponding points in all three images, thus providing 2-D and 3-D coordinates and tracking using the information in both image and object space. Reliability aspects such as occlusions, multiple solutions and different backgrounds will be analysed. The effect of a third image on reliability will be analysed.

OrthoviewTM--a softcopy orthophoto system: concept, production, and application

This paper presents the concept, production, and application of a softcopy orthophoto system. Although OrthoView is a commercially available computer software package, the paper concentrates on its overall design and functionality, especially its unique advantages in implementation which ensure a production environment in the production of softcopy orthophotos (called digital orthophotos in the rest of the paper). The goal and implementation of OrthoView is emphasized on commercially available, off-the-shelf computer hardware. OrthoView is a powerful, flexible, complete, fully tested, and low cost digital orthophoto workstation which is one of the very few stand-alone commercial products available to many potential users now.