Analysis of orthoretification process in a Worldview II image
ISBN 978-85-88783-11-9
Authors
1Colman, T.; 2Ferreira dos Santos, D.; 3Cintra, D.P.; 4Fernandes, M.C.
1UNIVERSIDADE FEDERAL DO RIO DE JANEIRO Email: thiagocolman@gmail.com
2UNIVERSIDADE FEDERAL DO RIO DE JANEIRO Email: sirdeivison@gmail.com
3UNIVERSIDADE FEDERAL DO RIO DE JANEIRO Email: danilabgis@gmail.com
4UNIVERSIDADE FEDERAL DO RIO DE JANEIRO Email: manoel.fernandes@ufrj.br
Abstract
The present study is located in Vale do Cuiabá, Itaipava District, Petrópolis, RJ, which has a basin circular type in the form of "shell". This fact exacerbates the risk of overflowing rivers in the region after high intensity rains, when several tributaries that "focus" their flow in a short time interval. This fact causes the greatest problems of waves and flood risks to health and life of the population located in the lower part of the basin. For this work was used an image obtained by the satellite Worldview-2, which passed through orthorectification process. When working with high-resolution images, especially in mountainous regions a good orthorectification procedure is essential, since these images are in an oblique view, which aggravates the distortion caused by the terrain relief. This process consists in the elimination of distortions caused by image acquisition process and by the relief. After the orthorectification process, the image can be considered geometrically reliable for the generation of cartographic documents and exact calculation of areas and distances. To make the image orthorectification, were pre-selected 32 points. For choosing these points some criteria were followed as primarily acquire points that were easily identified in the image itself and on the field. A local base station was installed in Trevo de Bonsucesso, Itaipava, Petrópolis with a Differential Global Positioning System (DGPS), Promark II device. The points were collected using Promark II and Promark III, with the same settings as the base unit. At each point, DGPS were allocated between 30 and 50 minutes, depending on the PDOP (Positioning Dilution of Precision). In the case of very high PDOP's the point was discarded from the analysis or collected in another time of day. After collection of points, the data were processed and corrected in Ashtec Solutions program. In order to validate a better method to orthorectify a high-resolution image in rugged terrain condition that reach the highest standards of National Cartographic Accuracy Pattern (PEC), were tested zero to five Ground Control Points (GCPs) to generate them. For the geometric accuracy assessment, Root Mean Square (RMS) was calculated using 21 permanent Independent Check Points (ICPs). The RMS value obtained for the model using only the RPC was 4.52 m and 0.74, with the use of Digital Elevation Model (DEM) of TOPODATA and Digital Elevation Model Hydrologically Consistent (DEMHC), respectively. As we expected the value of RMS decreases as increasing the number of GCP's. Thus, the orthoimages had better evaluation on National Cartographic Accuracy Pattern (PEC). Though increasing the number of GCP's caused a high geometric distortions that were noticed analyzing the borders of swimming pools and tennis court. Hence we decided that the best orthoimage was generated with three GCPs and using the DEMHC.
Keywords
Cartographic Accuracy Pattern; Vale do Cuiabá; TOPODATA