Reseach on a Gis-based Automatic Generation Algorithm for River Boundary Adaptive Irregular Meshes

Volume-fitted meshes have been widely used in different kinds of hydrodynamic models as well as in many hydro-mechanical models. A new method based on geographic information systems (GIS) has been presented to generate such irregular meshes automatically, which is also derived from classical algebraic methods on generating such meshes in hydrodynamics. Main inputs of the algorithm are DEM grids and centreline data of the river, a principle was put forward to express the variable flow direction numerically in a close approximation at the beginning, which is necessary to make sure those generated meshes be boundary-fitted in two dimensions; partitioning sections vertical to the flow direction throughout the river is the most key characteristics of classical algebraic methods on generation of hydrodynamic computation meshes, which is also one of the essential part of this algorithm, An assumption is made beforehand that slope value between each two adjacent nodes of the centreline could well approximate the flow direction everywhere thereby, thus provides a measurable means to express the variable flow direction at anywhere, as well as the direction of the section; a smoothening method is worked out to prevent overlapping sections from coming into being, also. Elevation computation using interpolation method is another important part of the algorithm, through which landscape model of the river could be reconstructed; a uniform relationship between the sampling direction and the flow direction at anywhere should be guaranteed in order to eliminate “wresting” phenomena in output results and “right-hand” rule has been applied here; another principle on judging the sampling direction from each two ending-point in every section has been introduced in detail, too; at last, a Bi-Linear Multinomial Interpolation method have been used in the computation of elevation value for each sampling points. Results of the algorithm in files and pictures have also been provided and explained at the end of this paper, which has proved the algorithm to be a good implementation of the pivotal interface for the integration of GIS and hydrological models. 1 Jiang Zhijun, Candidate of PhD in State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing(Lies-mars),Wuhan Univ., China. His main interest in research is Integration of “3S” (GPS, RS and GIS).