GISdevelopment.net ---> AARS ---> ACRS 1992 ---> Mapping from Space DEM Generation and Orthophoto Production With SPOT Imagery Kim Eui-Hong, Nah Bang-Hyun Systems Engineering Research Institute, KIST Park Hong-Gi Kyungwon University, Korea Abstract Digital Elevation Model (DEM) is basic and important for various fields which manages existing Geographic Information System (GIS) and remotely sensed data. In general, there are two kinds of method to generate DEM, one is to do by computerized algorithm only and another is using analytic plotter. The software package for DEM generation using SPOT Stereo image has been developed by the lab, in SERI and consists of bundle adjustment, image matching and spatial interpolation. In this paper, the exterior orientation parameters are acquired in the bundle adjustment procedure. And using these parameters, DEM are generated and orthophoto are produced. Although the systems has not yet been optimized, the results shows the high accuracy of the generation of image registered into a map. The acquired DEM data base will used for the layers of integrated GIS. Introduction Topographic mapping from SPOT stereo imagery has become possible on an operational basis. Many of the authors have studied the possibility of base map revisions and the accuracy of resulted ground coordinates (Konecy et al.. that the SPOT imagery is suitable for 1:50,000 to 1:100,000 topographic map. Bundle adjustment and image matching algorithms have been developed in SERI/KIST (Kim and Lee. 1991) to determine orthophoto position of SPOT imagery. Exterior orientation parameters can be estimated by scan linear or time function. To enhance the accuracy of orthophoto position of SPOT pixels, some modification of Bundle adjustment was needed and additional parameters were intrduced to correct geometric distortion. Also the ground coordinates of 23 control points were acquired by the conventional ground surveying. And image coordinates (line/column numbers) were measured to sub pixel level. After the GCP’s, geometric correlation was performed the matching points of two rectified images were found. Then DEM and orthophotos were produced. Characteristics of used SPOT imagery main exterior parameters of used SPOT stereo imagery are described in Table 1. Test Area TM (Transverse mercator) coordinates were used centered at (N380, E1270). The coordinates of upper left corner and lower right corner is (N316000, E228000) 501 pixels (5km) around Dae-Duk Science town. Bundle Adjustment Space resection for SPOT images requires the initial approximate values of the exterior orientation parameters. As initial values of h0 dp0 w0 image orientation (P) the angle of incidence (µ) were used zero respectively. Also the positional data from auxiliary data were interpolated to estimate initial position value of satellite position. In this study the coordinates of satellite position by WGS84 geocentric coordinates system were transformed to TM coordinates. The flow diagram for coordinates transformation is showed in figure 1. As additional parameters for correction of geometric distortion, 2nd order polynomials were used in two collinearity equations. DEM Generation DEM generation is performed by image matching algorithm. Histogram equalized imagery were used to enhance matching quality and efficiency. For area correlation matching the matching points were determined using 13 x 13 window matrix. With the corresponding pixel list ground coordinates were computed by space iintersection and generated DEM was randomly distributed. Finally regular gridbase of DEM with 10m x 10m resolution was produced from randomly distributed elevation data by interpolation method. Table 1. Parameters of SPOT Stereo imagery Figure 1 . Coordinate information of satellite position Orthophoto production The exterior orientation of SPOT image was obtained by bundle adjustment and DEM of the corresponding area was constructed by the DEM generation method. Then the X, Y position image was calculated according to collinearity equations. Figure 2 is the generated orthophoto of test area. Conclusion The software for bundle adjustment, DEM generation and orthophoto production with additional parameters to correct geometric distortion improved simultaneously. The results show the high possibility of the generation of image registered into a map, although test are is not large (5Km x 5Km) This study is respected to investigate the effect of different weight condition in bundle adjustment and to improve matching efficiency and accuracy in DEM generation. Figure 3 show bird-bye view DEM overlaid by the produced orthophoto images. Reference Chen. L. – C.L. H. Lee and S.C. Lee, 1988 DTM Generation using SPOT Digital Data”. ISPRS COM, 111, pp. 100-109. Gugan, D.J. and I.J. Dowman , 1988. Accuracy and Completeness of topographic mapping from SPOT Imagery”, Photogrammetric Record. (12 (72), pp. 787-796 IGN, 1988, Cartographic Production from SPOT Data at 1/5000 Scale”, IGN. Kim. Eui-Hong and Lee. Jong-Hun, 1991, DTM Generation and Orthophoto Production with SPOT imagery, ARCS, H-1-8. Konecny, G. et. al. 1987 Elevation of SPOT Imagery in Analytical Photogammetric Instruments”, P.E. & R.S.Vol. 53, No. 9, pp. 1223-1230. Li Deren and Cheng Jiyan, 1988. bundle Adjustment of SPOT imager” ISPRS. COM III, pp. 449-455.