RESEACH ON A GIS-BASED AUTOMATIC GENERATION ALGORITHM 
FOR RIVER BOUNDARY ADAPTIVE IRREGULAR MESHES 
Jiang Zhijun ^" , Li Deren *, Wang Wei *, Li Lan ? Yao Jing © 
? State Key Laboratory of Information Engineering in Surveying, Mapping and Remote Sensing, Wuhan Univ., China, 
430079,ziliujiang@sohu.com, dli@wtusm.edu.cn, wangwei@wtusm.edu.cn 
? School of Hydraulic and Electric Engineering, Wuhan Univ., China, 430072,lilan@163.com 
* School of Remote Sensing Information Engineering, Wuhan Univ. , China, 430079,cuckooyao@yahoo.com.cn 
PS WG 1V/6 Landscape Modelling and Visualization 
KEY WORDS: GIS, Hydrology, Integration, DEM/DTM, Representation, Algorithms 
ABSTRACT: 
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. INTRODUCTION not good at expressing the irregular variation of the river way, 
such as GRID. Triangulated Irregular Network (TIN) is 
In the case of doing numerical calculations in hydrodynamics characterized by the power to adapt the variation of land surface, 
and other mechanical or physical field, it is necessary to but can only be used in those hydrodynamic models based on 
generate some computation meshes in general need. For the finite-element method because of its irregular data structure. 
convenience of handling problems relating boundary of the 
object in research, such meshes are required to be boundary- A GIS-based algorithm of automatically generating these 
fitted or even volume-fitted, so they are named Volume-Fitted Volume-Fitted meshes is introduced in this paper; after this 
meshes in general speaking, which are usually made up of a set introduction, general principle of the algorithm is introduced in 
of irregular quadrangles (Lin Chaogiang, 1994). chapter 2; details of the algorithm are discussed in each sub- 
chapters in chapter 3; evaluations and conclusions of the 
Structured volume-fitted meshes have been widely used in computation results are provided and explained in the last 
different kinds of hydrodynamic models as well as hydro- chapter (chap. 4). 
mechanical models (Tang Yi, 1996). However, construction of 
such meshes in the research of natural rivers is not so efficient 2. PRINCIPLE OF THE ALGORITHM 
and automatic yet, many of the work are still need to be done 
by hand. In general, existing algorithms used to generate these volume- 
fitted meshes can be divided into three classes: algebraic 
Digital Elevation Model (DEM) has been well known for the method, angle-preserving transformation method and partial 
capability of spatial representation (Wang Jiayao, 2001); difference equation method (Lin Chaogiang, 1994), these three 
nevertheless, existing DEM data with regular data-structure are classes of algorithms have their own advantages and 
  
© 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). 
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