Accuracy assessment of an IKONOS derived DSM over urban and suburban area

(2007)

The availability of IKONOS stereo pairs has made it possible to generate Digital Surface Models of IKONOS data. Though it is possible to obtain a DSM from two images with a different viewing angle on the ... [more ▼]

The availability of IKONOS stereo pairs has made it possible to generate Digital Surface Models of IKONOS data. Though it is possible to obtain a DSM from two images with a different viewing angle on the same area, it is preferred to work with products ordered as stereo. Such stereo pairs have images that are made in the same orbital pass, resulting in a much better geometry of the stereo model. In this paper the accuracy of an IKONOS derived DSM of urban areas is assessed, based on DSMs from aerial photography and laser scanning. The quality and accuracy of a DSM derived from IKONOS stereo pairs has been assessed for test zones in two cities, Ghent and Liege. The test zones are characterized by a typical urban morphology (city center, residential, industry). The accuracy has been assessed for each of the different types of urban morphology in the study areas. An error surface is obtained by calculating the difference between the generated IKONOS surface models and reference surface models. This surface is used as a measure for the accuracy of the IKONOS surface model. Reference surface models from different origins are used (aerial photography, lidar, large scale 3D database). For the test zones in Liege, the relation between the DSM accuracy and different land cover types is studied in detail. Also the relation between DSM error and the topography will be investigated. [less ▲]

Generation of digital surface models and orthophotos of urban areas with IKONOS stereopairs

(2004)

The purpose of the presented research project is to investigate how present-day EO-technology can support local and regional decision-making, particularly in Belgium, and to develop prototype versions of ... [more ▼]

The purpose of the presented research project is to investigate how present-day EO-technology can support local and regional decision-making, particularly in Belgium, and to develop prototype versions of value-added products that fulfill some of the actual information needs, as expressed by Belgian authorities at the local and at the regional level. One of the technical research modules is focussing on the geometrical aspects of VHR data processing. Due to the capability of the IKONOS sensor up to an angle of 26° off-nadir, the satellite can take stereo image pairs. An IKONOS stereo pair consists of two images of the same location taken from two different perspectives on the same orbital pass. Although it is possible to obtain a stereopair from two images from different orbital passes and with a large time interval, it is proved that the stereopairs ordered from Spaceimaging or resellers gives better results (2004, Taillieu et al.). This paper describes the method applied for DSM generation from an IKONOS stereopair, over an urban area. The geometrical accuracy of the DSM is compared with the accuracy of a DSM, derived from aerial photography at scales of 1:12000 and 1:4000. The satellite-derived DSM is used for ortho-rectification of VHR imagery. The accuracy of the ortho-rectified images is compared with ortho-rectifications of the same images, based on the aerial photo DSM. [less ▲]

Improving spatial information extraction for local and regional authorities using Very-High-Resolution data - geometric aspects.

in International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences (2003), 34(XXX),

The purpose of the presented research project is to investigate how present-day EO-technology can support local and regional decision-making, particularly in Belgium, and to develop prototype versions of ... [more ▼]

The purpose of the presented research project is to investigate how present-day EO-technology can support local and regional decision-making, particularly in Belgium, and to develop prototype versions of value-added products that fulfil some of the actual information needs, as expressed by Belgian authorities at the local and at the regional level. To accomplish this goal the proposal addresses both technical and user-oriented issues, and builds on the experience of five research teams, each with its own background and particular know-how. The most important objectives of the project are: - to define optimal methods for improved spatial information extraction from high- and very-high resolution data, based on innovative processing techniques; - to identify useful EO-applications at the level of local and regional decision making that are made possible by applying the information extraction methods that will be developed; in this case especially 3D information - to define and develop value-added core data products that will support these applications, and that can be consulted with easy-to-use, widely available IT-tools (CD-ROM, Internet, …). One of the technical research modules is focussing on the geometrical aspects of VHR data processing. In terms of spatial resolution, VHR data have the required level of detail to resolve individual objects in the landscape, in a similar way as airborne data. As such, they have the potential of becoming a useful data source for the extraction of detailed, object-related information, and for the production of large-scale cartographic reference data. The geometry of VHR sensor data, however, completely differs from the geometry of aerial photographs (Bethel et al., 2001). Research is going on to evaluate the geometric qualities of present and future VHR standard data products, from the moment they become available, and to examine what level of geometric accuracy is attained with these data, depending on image parameters, processing strategies, and terrain characteristics (Zhou and Li, 2000). The main objectives of the research module on geometric aspects of VHR data processing are: a) to define an optimal procedure for the derivation of envelope DSMs (Digital Surface Models) and ortho-photoplans from VHR data; b) to develop a theoretical model to study the effect of the oblique viewing angle of VHR data on image displacements caused by building height and relief; c) to evaluate the geometric accuracy of satellite-derived envelope DSMs and ortho-corrected image data in comparison with similar products obtained by means of large-scale aerial photography. The module about geometrical aspects is divided into six specific tasks. a) GPS database creation b) Creation of reference envelope DSMs based on aerial photography c) Ortho-rectification of VHR images and aerial photography based on reference DSMs d) Evaluation of the quality of VHR geo-referenced data e) Modelling of displacements caused by terrain morphology and sensor viewing angle f) Development of envelope DEMs from VHR stereoscopic imagery The project is now in the stage where the quality of the georeferenced and orthorectified data is evaluated. [less ▲]