Automatic extraction of drainage network in Digital Elevation Models of high spatial resolution
ISBN 978-85-88783-11-9
Authors
1Silva, L.; 2Francisco, C.
1INSTITUTO BRASILEIRO DE GEOGRAFIA E ESTATISTICA Email: luciana.silva
2UNIVERSIDADE FEDERAL FLUMINENSE Email: crinsf@vm.uff.br
Abstract
Drainage identification for Brazilian systematic mapping is done by photointerpretation from stereoscopic model restitution. The developments of Geotechnology allowed automatic extraction of drainage networks through algorithms applied to Digital Terrain Modelling (DTM). On the digital restitution, DTM may be constructed from the stereoscopic models of the aerial photographs. Examples of these models have been produced by the RJ-25 Project, developed by Instituto Brasileiro de Geografia e Estatística (IBGE), which aims to produce 1:25.000-scale topographic maps of Rio de Janeiro state from stereoscopic models obtained by aerophotogrammetric survey in 1:30.000-scale. This paper aims to analyze drainage patterns automatically extracted from a DTM with spatial resolution greater than 20m in three different topographic areas, comparing to the analogic mapping of the 1:25.000-scale maps of the Project RJ-25 area. Project RJ-25 DTMs with spatial resolution of 1.5m, 5m and 20m from two different test areas were used in this study. Drainage information was automatically extracted with Arc GIS Spatial Analyst extension. Results pointed that the drainage networks extracted from the three different resolutions DTM for a hilly terrain have achieved the requirements. The 5m-resolution model has presented a better result when comparing to the conventional process of generating drainage networks for 1:25.000 scale maps. However, in some areas vegetation height affected the results. On the flat areas, the experiments with the three resolutions haven’t achieved adequate results related the shape, position and density of the drainage. Skilled photointerpretation professionals pointed out that it is very difficult to depict drainage on this type topography, requiring specific knowledge on the area for this task. Hence, automatic extraction of the drainage shouldn’t be used on Cartographic Production. Photogrammetric restitution is still necessary for drainage networks extraction. Nevertheless automatic process may be useful for reviewing conventional work as well as preliminary and qualitative evaluation of the drainage patterns of the study area.
Keywords
digital elevation model; geoinformation; aerophotogrammetric restitutio