Key Techniques And Applications Of Spatial Visibility Analysis

The ability of spatial analysis is one of the most important implementations of GIS, which is widely regarded by many scholars in the world. However, it is still a weak part in most GIS systems. The objects of GIS, geographic objects, depend on geospatial regional differences. The regional differences are limited by human being's perception and visual scope even though the modern technologies can help us to some extent. We always observe, cognize and modeling geographic environment through our visibility. The observation and cognition of geographic environments are the primary contents in spatial visibility analysis, which emphasize on the geospatial visibility extend and resolution in methods. This is fundamental for perceiving and analyzing geo-space. Based on the research of geo-space, this paper discusses visual and psychological space, and advances the concepts and classification of visibility. The concepts are used to interpret the essence and internal relations of visibility.As a principal part for natural space, human are the fundamental parts in spatial visibility analysis. The paper first discusses the human visual physical enginery, and furthermore analyzes conception and cognition in visibility analysis, as they are the root of the way that we conceive the geo-space. Though they are different in the process approaches, the viewshed and resolution in spatial vision are especially fundamental in the study of spatial visibility. In certain extension we can say spatial visibility analysis includes all the contents of visual geospatial analysis. And we will discuss the above contents in chapter 2.Spatial visibility analysis is expressed as spatial extension and spatial resolution in the quantitative analysis, which is in the scope of spatial scale. The paper discusses in detail about spatial scale in the field of geographical information science. The problem of spatial scale is the confusion but fundamental aspect in GIScience. The issue of spatial scale is present in all forms of spatial analysis and has been identified as one of the most ubiquitous and fundamental aspects of spatial research. Scale provides the required link between what is studied and the observation. The core of the problem is the nature of scale dependency and scale-linkage. Any research dependent on scale is constrained by the spatial extension and resolution of the observed objects. The objective of the study is to conceptualize, characterize and interpret scale effects in spatial visibility and cartographic representation, to reveal the essence of linkage between of spatial of scale and cartographic generalization. The definitions and meanings involved in the scale discussed in this paper are delivered, such as cognitive scale, spatial extend, spatial resolution and map scale. Then it discussed the content and relationships of scale from different analytical levels.The main calculations of spatial visibility analysis are visibility and viewshed. On a plane they refer to viewshed analysis in the polygon environment and as it is described as surveillance problem in practice. Due to different position, route, movement and polygon environment of viewpoints, plane surveillance can be expressed in many formats. The paper discusses the description and solution methods of the vertex supervisor in typical art gallery problems (AGP) for example. The core problems of AGP are polygon segmentation and vertex coloring, difficulty and particularity lie on its solution for optimize the worst. The paper concentrates on the problems about vertex supervisor and internal supervisor, and discusses polygon segmentation problem based on the sight movement, presents key events method about channel and even its concrete solution, which can effectively explore the viewshed in the polygon environment. And finally we simplydiscuss dynamic and route planning.Terrain is another important study object of GIS spatial visibility. The calculation methods and approaches of 3D relief visibility analysis are different because the differences in the factors and complexities about the terrain characteristics. The chapter 4 will firstly analyze the objective and subjective factors of terrain visibility analysis such as relief characteristics, fundamental elevation data, the choice of viewpoint and capture methods of elevation values, the characteristics of LOS, the characteristics of numerical value, visual parameters control and so on. Those factors will be deal in the practice combined with different circumstances. Terrain visibility calculation consists of LOS calculation and viewshed calculation. Generally speaking visibility calculation is the foundation of viewshed calculation and still there are many new approaches to calculate viewshed directly such ad multi-agent simulation. The paper discusses the principle of visibility and viewshed calculation. The paper delivers an incremental method to calculate terrain visibility with comparison of elevation difference using increments base on grid size. The method is more simple, lower complexity and easier to realize.Visibility analysis depends mostly on the methods that we process data, so the result will be a little different. In this paper the fuzzy and accuracy of the result will be discussed. LOS visibility and viewshed is the basic visual expression of relief, and we provide different analytical results through different visibility analysis to satisfy different demands and take their implementations in martial affairs as examples. In chapter 4 we also discussed the relationship between terrain visibility analysis and perception and behavior decisions. And after analyzing the relationship between visibility and terrain characteristics, we found they are non-high correlation.Spatial visibility analysis is tightly relative to human vision, and the techniques of visibility analysis are used to plan, analyze and evaluate the visual landscape, such as urban landscape, road landscape, scene landscape and archeology landscape. The paper takes Mt. Mo resort as an example in fifth chapter, calculates the viewshed of viewpoints in Mt. Mo to estimate the scope, characteristics of viewshed to see whether it can browse other viewpoints and scenes. The paper uses the integration of GIS data to estimate the connectivity of viewpoints. In order to stand out the effects of viewpoints and give us the personally perceptions on the scene, we construct the virtual Mr. Mo landscape system, through which we can browse the beautiful scenes. Landscape system is an efficient tool to predict and estimate urban landscape system, and the paper uses the spatial visibility analysis to protect mountain landscape during urban construct and discusses the estimate methods of urban landscape based on visibility analysis.When the results of spatial visibility analysis feed back to human, they will affect our behaviors and decisions, which is related with human cognition. In urban space, we move in streets and the results of visibility can be presented in two ways: how much we can see and how long we can see. And naturally we may have certain trend to move or take direction. Spatial visibility analysis is a novel method in urban morphology and spatial configuration, which is an important tool in space syntax. The paper first discusses the concepts of visibility centricity, and quantifies the parameters of visibility analysis on viewpoints to explore urban morphology of street network with pedestrian movement. The paper takes wuhan zhongnan district as an example. This method of pedestrian flow with visibility can be expended to other urban group, such as car flow, bike flow. Urban morphology determines the urban flow, and urban group affect inversely the configuration and layout of urban infrastructures, such as garden, plaza.Since spatial scale is foundation of spatial visibility analysis, which mainly embodies in spatialextend and resolution, what is the coherent constraints and what is the intrinsic relationships between them, how do they response to geographic space? We discuss these content about visibility analysis and multi-scale in seventh chapter. The paper first make known that spatial resolution of visibility is the criterion when we percept and cognize our geographic environment. We have different cognition level with different resolution, then gain different spatial pattern, which is the essence of scale in map generalization geographic landscape. The paper discusses constrains between extend and resolution is the potential standard of analysis and process of geodata, which is completely accord with human vision system.