Contour filling algorithm of spatial and temporal rainfall distribution based on multi trees in 3D virtual environment

A contour filling algorithm for visualization of spatial and temporal distributions of rainfall in a three-dimensional watershed virtual environment is put forward in this paper.A closed curve is constructed by using watershed boundary points and generating open contours,and a modified Simpson-area method is used to make all the contours in the same direction.The inclusion relations of contours are determined by a ray intersection method and the contour features,and after designing the contour data structure a multi-tree data structure is introduced to construct topological relations of the contours.The color bands of contours are selected by the number of contour levels,and the choice of filling color depends on the multi-trees relationship of contours.This algorithm of rapid vector filling is effective in the cases of any scale,attribute values and boundary conditions in three-dimensional simulation system.Application to visualization of the rainfall process measured in the upper Yangtze reaches verifies the proposed algorithm.