GENERATION OF DIGITAL ELEVATION DATA USING SPACE-IMAGERIES

Abstract

Digital Elevation Model (DEM) is subset of Digital Terrain Model (DTM) in which the terrain elevations are expressed against their planimetric positions. DEM is an important tool for many applications in CIVILENGINEERING as well as for generating many graphic products, such as perspective views, slope zones, profiles, cross-sections and contours. The data for generating a DEM may be acquired from either the existing maps, or ground surveys, including GPS surveys or aerial photographs. Now-a-days the availability of high resolution stereo-data products from satellites such as SPOT, MOMS etc. have given impetus to the possibility of deriving the elevation data from these, for the preparation of topographic maps as well as generation of DEMs. The launching of IRS-IC and IRS-ID satellites by India in Dec. 95 and Sept. 97 respectively has provided high quality stereoimages with spatial resolution of 5.86 m and a revisit of five days. Whereas some isolated efforts to generate spatial data from these imageries have been reported in literature a definite answer to suitability of these and achievable accuracy from these has not yet been conclusively reported. The main aim of this work was to examme the suitability of stereo images of IRS-IC for height determination and to develop a methodology, based on analytical photogrammetric principles, for the generation of digital elevation data using IRS-IC digital stereo images (panchromatic data), and to assess the accuracy of the generated digital elevation data. The methodology adopted in this research work is based on analytical photogrammetric principles. A modified Space Resection/Intersection method has been li developed to generate 3-D information from IRS-IC stereo data, for this research. Two areas, nearer to Roorkee one covering Dehradun and second Nainital in India for which digital stereo data was available, have been selected for investigations. The orbit models were created for both areas and from these elevation data for a number ofpoints were extracted. The accuracy ofthe generated elevation data was found out by analyzing the errors at the check points. DEMs were generated using MGE GIS software and contours were generated for stereo models of both areas. For the computation of various stages, programs have been developed in UNIX system using Fortran 77. The results for Dehradun area, which has moderately undulating terrain compared to Nainitial area, have been found to be fairly good and acceptable. It has been concluded that IRS-IC stereo data with proper control is suitable for topographic mapping at scales smaller than 1:50,000 in moderately undulating areas. The generated DEM from IRS-IC stereo data may be used to produce contour maps, perspective views, topographic maps, thematic maps, etc., to serve as base map for several GIS based applications. 111