of stereo Ikonos imagery shows that 5-to 10-m contour lines can Recent high-resolution satellite images provide a valuable new be derived with the highest topographic standard (Toutin et al., data source for geospatial information acquisition. This paper 2001). As for geospatial feature extraction for topographic mapaddresses building extraction from Ikonos images in urban ping, Baltsavias et al. (2001a) and Fraser et al. (2001; 2002) presareas. The proposed approach uses the classification results ent results on building extraction from Ikonos stereo images. A of Ikonos multispectral images to provide approximate locacomparative study with the results obtained from aerial phototion and shape for candidate building objects. Their fine graphs concludes that about 15 percent of the building areas, as extraction is then carried out in the corresponding panchromeasured in aerial images, cannot be modeled using Ikonos matic image through segmentation and squaring. The ECHO images. An assessment based on 19 GPS surveyed check points classifier is used for supervised classification while the ISODATA at roof corners suggests that the Ikonos-derived building model algorithm is used for unsupervised classification and subsecan reach an accuracy of better than 1 meter both in planimetry quent image segmentation. The classification performance is and elevation (Baltsavias et al., 2001a). Sohn and Dowman evaluated using the classification confusion matrix, while the (2001) used a local Fourier transformation to analyze the domifinal building extraction results are assessed based on the nant orientation angle in a building cluster and extract rectilinmanually delineated results. A building squaring approach ear building outlines from Ikonos imagery based on a binarybased on the Hough transformation is developed that detects space partitioning tree. Dial et al. (2001) present an investigaand forms the rectilinear building boundaries. A number of tion on automated road extraction in wide suburban roads. sample results are presented to illustrate the approach and Regarding the fundamental methodology in geospatial feademonstrate its efficiency. It is shown that about 64.4 percent ture extraction from aerial and space images, abundant experiof the buildings can be detected, extracted, and accurately ence has been gained in the past few years. A collection of stateformed through this process. Remaining difficulties are high of-the-art articles can be found in the periodical proceedings percentage false alarm errors caused by the misclassification edited by Grü n et al. (1995), Grü n et al. (1997), and Baltsavias et of road and building classes as well as occlusion and shadows al. (2001b). Mayer (1999) presents a comprehensive survey on that may mislead the extraction process. the techniques used for image-based building extraction. These collections and surveys suggest a common understanding that Recent successfully launched satellites (Ikonos, EROS, Quick-multiple data sources and external knowledge or models about the buildings a...

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A suite of geometric sensor and platform modeling tools has been developed which have achieved consistent subpixel accuracy in orthorectification experiments. Aircraft platforms in turbulent atmospheric conditions present unique challenges and have required creative modeling approaches. The geometric relationship between an image point and a ground object has been modeled by rigorous photogrammetric methods. First and second order Gauss-Markov processes have been used to estimate the platform trajectory. These methods have been successfully applied to HYDICE and HyMap data sets. The most important contributors to the subpixel rectification accuracy have been the first order Gauss-Markov model with control linear features.