土地定级中定级因子扩散算法研究

定级因子扩散用来计算定级因子对定级单元的作用分值,是整个土地定级的关键.GIS在土地定级中的应用提高了土地定级的效率,但是当用传统GIS方法计算定级因子对定级单元的作用分值时,一般采用定级因子直线距离衰减方法,这种方法忽略了定级因子与定级单元之间自然地物和人文地物阻隔的影响.考虑了阻隔物对定级因子扩散影响的基础上,提出了两种不同扩散方法以避免空间直线衰减扩散方法的不合理性.一种是带通道表的桥扩散方法,通过自动生成土地通道表,能在多阻隔块和多座桥的情况下快速地进行定级因子扩散,提高了计算效率;另一种是实际道路最短到达时间扩散方法,使定级因子扩散的结果更加合理.接着通过实例对所有3种扩散方法进行了比较,分析后两种方法的合理之处.最后总结了所有3种方法的优缺点和适用场合,指出了在实际应用中,应该根据各自的特点和具体的要求选择合适的方法.

A Algorithm of the Grade Factors' Diffusion in Land Grading

The grade of land is affected by nature,society and communication conditions.The purpose of land grading is to quantify and synthesize these conditions that are called grade factors and to classify the land units under the diffusion of these factors.Therefore,the grade factors' diffusion calculates the effect value of the grade units affected by the grade factors and it is the key to the land grading.GIS can make powerful spatial analysis and work with the database.With its application,the process of land grading speeds up.In land grading,as the distance between the grade factors of same kind and the grade units increases,the grade factors gradually loose their effect on the grade units in a mathematic rule.Traditionally,the spatial line distance between the grade factors and the grade units is adopted to calculate the effect value of the grade units affected by the grade factors.So in graph,the effect value is represented by a series of contours with attenuating value.But this method ignores the impact of the blocks such as rivers,lakes,railways and highways.In order to avoid the irrationality of spatial line distance attenuation and consider the impact of the blocks,two different factors' diffusion methods are given.At the same time,the principles and the algorithms of the two methods are introduced in detail.One of the factors' diffusion methods is to diffuse through bridge.Here a way to create the land's path table automatically is put forth,and it advances the calculation speed of the effect value of the grade units affected by the grade factors greatly when there are more than two blocks or bridges.Another one of the factors' diffusion methods is to diffuse by the shortest access time on the real road,which is more reasonable and consistent with the real price of the land.After that,an example including all these three factors' diffusion methods is given and the graphs calculated by these three different methods are compared and the reasonability of the last two methods is analyzed.Finally,both the advantages and disadvantages of all these three methods are concluded.It is pointed out that suitable methods should be chosen according to their characteristics and particular requests in application.