Jae-Hong Yom

Automatic recovery of building heights from aerial digital images

Recently in the field of telecommunication, there is much interest in geo-surface characteristics of urban areas. Geophysical properties of urban features are now incorporated with accurate positional information to model the telecommunication environment. In this study, three dimensional buildings are geometrically reconstructed from existing vector maps and aerial images. Accurate digital vector maps are easily available in Korea. However existing maps, which had been produced for GIS applications, do not have height information which is critical to three dimensional building reconstruction. Image matching techniques were applied to aerial image stereopairs to automatically extract the height information of buildings. Planimetric coordinates from vector maps were used as initial guides in the process. Future studies can be undertaken to link geophysical properties to the three dimensional spatial objects reconstructed from this study thus bringing the telecommunication environment model closer to reality

Telecommunication modeling by integration of geophysical and geospatial information

Both geophysical and geospatial data provide important information in the establishment of the optimal telecommunication systems especially in the mobile telecommunication environment. The objective of this study is to utilize geophysical properties and geospatial information in the analysis of the telecommunication environment through point-to-point wave propagation modeling. Geophysical properties associated with wave propagation parameters of the Earth surface were analyzed based on land classification using fused imagery of Landsat ETM+ and Ikonos images. Three-dimensional geospatial information was obtained by processing stereo aerial images. The results show that the accurate geospatial information and geophysical property of the surface improve the prediction of receiving power of the receivers located near corners of the buildings where diffractions occur. The wave propagation model developed from accurate telecommunication environment could be applied to cell planning

Automatic 3D Building Reconstruction by Integration of Digital Map and Stereo Imagery for Urban Area

Three dimensional model of urban areas is useful in several applications. In urban administration, perspective views derived from three dimensional model are used by city planners for landscape analysis. Three dimensional models are also used in modeling telecommunication environment. Building heights are important in searching for the optimal locations of transmission antennas especially in mobile telecommunication for cell planning. Furthermore, reconstructed 3D buildings are also essential in generating ‘true’ digital orthophotos where occlusion areas caused by tall buildings are eliminated. This paper introduces an automated method of building height and eventually 3D building reconstruction which involves the integration of existing 2D vector geodata (i.e., digital maps) and stereo aerial imagery. Accurate 2D vector geodata of major cities in Korea are available at the scale of 1/1,000. The vertical line locus method has been deployed to recover building heights. Building footprint in the 2D vector geodata is used in locating the vertical guideline along the building edges formed by building sides. Digital elevation model (DEM) was also generated from the contour layer which is included in the vector geodata. DEM values at the foot of the buildings were used as initial searching locations. At a preset incremental value of height along the vertical guideline, evaluation based on the cross correlation image matching technique was carried out to test if the top of the building has been reached. Buildings are reconstructed with flat roof surfaces that are typical shape of the buildings in the study site.

TRIFLE DIFFERENCE APPROACH TO LOW EARTH ORBITER PRECISION ORBIT DETERMINATION

A precise kinematic orbit determination (P-KOD) procedure for Low Earth Orbiter(LEO) using the GPS ion-free triple differenced carrier phases is presented. Because the triple differenced observables provide only relative information, the first epoch`s positions of the orbit should be held fixed. Then, both forward and backward filtering was executed to mitigate the effect of biases of the first epoch`s position. p-KOD utilizes the precise GPS orbits and ground stations data from International GPS Service (IGS) so that the only unknown parameters to be solved are positions of the satellite at each epoch. Currently, the 3-D accuracy off-KOD applied to CHAMP (CHAllenging Min-isatellite Payload) shows better than 35 cm compared to the published rapid scientific orbit (RSO) solution from GFZ (GeoForschungsZentrum Potsdam). The data screening for cycle slips is a particularly challenging procedure for LEO, which moves very fast in the middle of the ionospheric layer. It was found that data screening using SNR (signal to noise ratio) generates best results based on the residual analysis using RSO. It is expected that much better accuracy are achievable with refined prescreening procedure and optimized geometry of the satellites and ground stations.