tailieunhanh - Practical GIS Analysis - Chapter 8

Cho đến bây giờ, bạn đã làm việc chủ yếu trong thế giới vector của các điểm, đường, và đa giác. Đây là những tính năng riêng biệt đại diện bởi X, Y tọa độ, và tính năng từng có một số nhận dạng duy nhất. Lưới là khác nhau bởi vì họ có thể đại diện cho một bề mặt liên tục thay vì các tính năng riêng biệt. Nhìn chung, mô hình lưới dữ liệu GIS có một số lợi thế tương đối so với mô hình vector dữ liệu GIS điểm, đường, và đa giác: . | Chapter 8 Grid Analysis INTRODUCTION GRID AND VECTOR GIS WORLDS Until now you have worked mainly in the vector world of points lines and polygons. These are discrete features represented by X Y coordinates and each feature has a unique identification number. Grids are different because they may represent a continuous surface instead of discrete features. In general the grid GIS data model has several advantages relative to the vector GIS data model of points lines and polygons Grids allow for faster analysis especially for any overlay type analysis Grids allow for modeling continuous surfaces such as wildfire or oil spill spreads or determining the optimal path through a surface. Grid is the natural model for many data sources in natural resources such as digital elevation models scanned maps and land cover data derived from satellite data. Grids allow you to represent the world as a fuzzier system. For example in the vector world vegetation polygons are often assigned a vegetation type from visual interpretation of aerial photographs. Typically relatively large polygons are delineated because of an arbitrary minimum mapping unit criteria used during the air photo interpretation. With land cover grids the minimum mapping unit is the size of the grid cell and therefore heterogeneous areas can be better represented. In the vector world polygons are assigned as one homogeneous land cover class. In the grid world the same area may be several land cover classes and the probability of correct classification of each grid cell can also be stored. The vector model of points lines and polygons does have some advantages over the grid model Since features are stored as X Y coordinates it usually takes less disk space to store points lines and polygons relative to grids that have the same precision of spatial detail. The vector model allows for modeling of linear networks and the incorporation of measured events via dynamic segmentation. The vector model is a natural model for