Introduction to GIS.ppt

1、Introduction to GIS,Dr. A.K.M. Saiful Islam,Institute of Water and Flood Management (IWFM) Bangladesh University of Engineering and Technology (BUET),Presentation outline,Introduction to GIS Components of GIS Sources of geospatial data Geospatial databases ESRI Data models,Introduction to GIS,What i

2、s GIS ?An Information System that is used to input, store , retrieve, manipulate, analyze and output geographically referenced data or geospatial data, in order to support decision making for planning and management of land use, natural resources, environment, transportation, urban facilities, and o

3、ther administrative records,Why GIS is essential ?,Common problems of handing geospatial information:Geospatial data are poorly maintained. Maps and statistics are out of date. Data and information are inaccurate. There is no data retrieval service. There is no data sharing.,GIS Versus Manual Works,

4、Benefits once GIS is implemented,Geospatial data are better maintained in a standard format. Revision and updating are easier. Geospatial data and information are easier to search, analysis and represent. More value added product. Geospatial data can be shared and exchanged freely. Productivity of t

5、he staff improved and more efficient. Time and money are saved. Better decision can be made.,Basic Functions of GIS,Remote Sensing and GIS in Water Management Dr. Saiful Islam, IWFM, BUET,GIS as Multidisciplinary Science,Area of GIS Applications,GIS for decision support,Components of GIS,Key compone

6、nts of GIS are: Computer system, geospatial data, and users Sources of geospatial data are: Digitized maps, aerial photographs, satellite images, statistical tables, and other related documents,Computer System,Geospatial Data,Users,Figure: Key components of GIS,Classification of Geospatial Data,Grap

7、hical data (called geometric data)Attributes (called thematic data),Data Model,A set of guidelines to convert the real world (called entity) to the digitally and logically represented spatial objects consisting of the attributes and geometry.Types of geometric data modelVector Model Model uses discr

8、ete points, lines and/or areas corresponding to discrete objects with name or code number of attributesRaster Model - Model uses regularly spaced grid cells in specific sequence. An element of grid cell is called a pixel (picture cell),Example of vector based model,Vector model,Example of raster rep

9、resentation,256 color,more colors,Components of Raster model,Cell size- Each cell has a width and height and is a portion of the entire area represented by the raster,Cell location - The location of each cell is defined by its row or column location within the raster matrix.,Cell value - Each cell h

10、as a value.,Raster model, otherwise known as a raster dataset (image), in its simplest form is a matrix (grid) of cells.,Geometry and Topology of Vector Data,Geometry Spatial objects are classified into point object such as meteorological station, line object such as highway and area object such as

11、agricultural land, which are represented geometrically by point, line and area respectively Topology refers to the relationships or connectivity between spatial objects,Topological of Spatial Objects,Attributes,Attributes are often termed “thematic data“ or “non-spatial data“, that are linked with s

12、patial data or geometric data.An attribute has a defined characteristic of entity in the real world. Attribute can be categorized as normal, ordinal, numerical, conditional and other characteristics. Attribute values are often listed in attribute tables which will establish relationships between the

13、 attributes and spatial data such as point, line and area objects, and also among the attributes,Map Layers,Spatial objects in digital representation can be grouped into layers.For example, a map can be divided into a set of map layers consisting of contours, boundaries, roads, rivers, houses, fores

14、ts etc.,Sources for GIS data,Analog maps Aerial photographs Satellite image,Remote Sensing and GIS in Water Management Dr. Saiful Islam, IWFM, BUET,Ground survey with GPS Reports and publications,Data Acquisition Methods,Concept of Spatial Database,A spatial database is defined as a collection of in

15、ter-related geospatial data, that can handle and maintain a large amount of data which is shareable between different GIS applications. Required functions of a spatial database are as follows. - consistency with little or no redundancy. - maintenance of data quality including updating - self descrip

16、tive with metadata. - high performance by database management system with database language. - security including access control.,Design of Spatial Database,The following parameters should be well designed. storage media Volume, access speed and on line service should be considered. partition of dat

17、a Choice of administrative boundaries, map sheets, watersheds etc. will be made in consideration of GIS applications standards Format, accuracy and quality should be standardized. change and updating Add, delete, edit and update should be well controlled by the database manager. scheduling Data avai

18、lability, priorities, data acquisition etc. should be well scheduled. security Copyright, back up system and responsibilities should be well managed.,partition of data,Spatial Data Models,Hierarchical Relational Object oriented,1. Hierarchical Model,Stores data as hierarchically related to each othe

19、r. Record shape are tree structure.,BUET,Faculty of Civil Engineering,Faculty of Architectural,CE,WRE,URP,Archit,(Contd),Advantages High speed access to large databases Easy to update- (to add or delete new nodes)Disadvantages Links are only possible in Vertical Direction (from top to bottom) but no

20、t for horizontal or diagonal unless they have same parents. For example, it is hard to find what is the relation between URP and DCE from this data model.,2. Relational Model,Based on two important concepts:Key of relation - one to one, one to many, many to manyPrimary attribute which cant be duplic

21、ate,Course table,Employee Table,Employee Table,Course Table,*,*,Many to many relationship,Find the relationship between this two tables in the BUET Library,Book Table,Students Table,One to one Many to Many One to Many,?,Structural Query Language (SQL),SQL is used to perform query in relations databa

22、ses.For example, find the name of the employee who have spend more than 10,000 this year to attend different courses.SELECT Employee.Name, Course.Fees FROM Employee WHERE Employee.CourseID = Course.CourseID AND Fees = 10,000 The answer is : Rahim,3. Object Oriented Model,BUET,Departments,Institutes,

23、CE,WRE,DCE,IWFM,URP,AIT,Faculty, Staff, Students,Attributes:,Is a,Is a,Is a,Is a = Inheritance Part of = association,Part of,Part of,Object Oriented Database,An Object Oriented model uses functions to model spatial and non-spatial relationships of geographic objects and the attributes.An object is a

24、n encapsulated unit which is characterized by attributes, a set of orientations and rules. An object oriented model has the following characteristics. generic properties : there should be an inheritance relationship. abstraction : objects, classes and super classes are to be generated by classificat

25、ion, generalization, association and aggregation. adhoc queries : users can order spatial operations to obtain spatial relationships of geographic objects using a special language.,ESRI Data models Advancements in GIS,Vector Data models Shape file Coverage Composite Data model TIN Regions Route Data

26、base Geodatabase,ESRIs models,Shapefiles as non-topological data format. Shape file treats points are pair of x, y coordinates, a line as a series of points and a polygon as a series of lines. Can be displayed more rapidly on monitors. Interoperable among other software.Coverage as topological based

27、 vector data format. A coverage can be point coverage, line coverage or polygon coverage. Connectivity: Arcs connect to each other at nodes. Area definition: An area is defined by a series of connected arcs. Contiguity: Arcs have directions and left and right polygons,Data models for composite featu

28、res,TIN Triangulated irregular network data model approximates the terrain with a set of non-overlapping triangles.Regions is defined here as a geographic area with similar characteristics. A coverage feature class that can represent a single area feature as more than one polygon.Routes - is a line

29、feature such as highway, a bike path, or a stream but unlike other linear features, a route has a measurement system that allows linear measures to be used on a projected coordinate system.,Triangulated Irregular Network (TIN),TIN,TIN & Contour,Triangulated irregular network. A vector data structure

30、 used to store and display surface models. A TIN partitions geographic space using a set of irregularly spaced data points, each of which has an x-, y-, and z-value.These points are connected by edges into a set of contiguous, non-overlapping triangles, creating a continuous surface that represents

31、the terrain.,Components of TIN,The nodes originate from the points and line vertices contained in the input data sources. Every node is incorporated in the TIN triangulation. Every node in the TIN surface model must have a z value.Every node is joined with its nearest neighbors by edges to form tria

32、ngles which satisfy the Delaunay criterion. Each edge has two nodes, but a node may have two or more edges. Because edges have a node with a z value at each end, it is possible to calculate a slope along the edge from one node to the other. Each triangular facet describes the behavior of a portion o

33、f the TINs surface. The x,y,z coordinate values of a triangles three nodes can be used to derive information about the facet, such as slope, aspect, surface area, and surface length. The hull of a TIN is formed by one or more polygons containing the entire set of data points used to construct the TI

34、N. The hull polygons define the zone of interpolation of the TIN. Inside or on the edge of the hull polygons, it is possible to interpolate surface z values, perform analysis, and generate surface displays. Outside the hull polygons, it is not possible to derive information about the surface. The hu

35、ll of a TIN can be formed by one or more polygons which can be non-convex.,Nodes,Edges,Triangles,Hull,Delaunay Triangulation for TIN,A method of fitting triangles to a set of points. The triangles are defined by the condition that the circumscribing circle of any triangle does not contain any other

36、points of the data except the three defining it. It is a method which produces triangles with a low variance in edge length. The resulting triangles may be used as an irregular tessellation for interpolation of other points on a surface.,Region and polygon -1,Polygons do not overlap and completely c

37、over the area being represented (do not contain any void areas).In a region, the polygons representing geographic features can be freestanding, they can overlap, and they need not exhaust the total area.,Region and polygon -2,Another premise of polygons is that each geographic feature is represented

38、 by one polygon. This is extended for regions, so that a single geographic feature can be represented by several polygons.,Region and polygon -3,As with points, lines, and polygons, each region is given a unique identifier. As with polygons, area and perimeter are maintained for each region. Constru

39、cting regions with polygons is similar to constructing polygons from arcs. Whereas a polygon is a list of arcs, a region is simply a list of polygons. One important distinction exists: the order of the polygons is not significant.,Route,In ArcGIS, the term route refers to any linear feature, such as

40、 a city street, highway, river, or pipe, that has a unique identifier and a common measurement system along each linear feature.,A collection of routes with a common measurement system is a route feature class. Each route in the feature class will also have a unique identifier. Line features with th

41、e same unique identifier are considered to be part of the same route:,Route feature classes are created and managed as line feature classes in the geodatabase. You can also use route feature classes from ArcInfo coverages and polyline shapefiles that include route identifiers and measured features.,

42、Point events along Route,Point events occur at a precise point location along a route. Accident locations along highways, signals along rail lines, bus stops along bus routes, Wells or gauging stations along river reaches, pumping stations along pipe lines, Manholes along city streets and valves alo

43、ng pipes are all examples of point events. Point events use a single measure value to describe their location.,Line events along Route,Line events describe portions of routes. Pavement quality, salmon spawning grounds, bus fares, pipe widths, and traffic volumes are all examples of line events. Line

44、 events use two measure values to describe their location.,Polygon events along Route,Locating polygon features along routes computes the route and measure information at the geometric intersection of polygon data and route data. Once polygon data has been located along routes, the resulting event t

45、able can be used, for example, to calculate the length of route that traveled through each polygon.,Examples: Soils, spillways, areas of inundation, or hazard zones along river reaches Wetlands, hazard zones, or town boundaries along highways,The route feature class for streams provides measures alo

46、ng the streams using river reach mile. Point and line event tables record the route ID and location along each river reach. These event tables can be used to locate point and line events.,Example of Route,Hydrologists and ecologists use linear referencing on stream networks to locate various types o

47、f events,Route system,A collection of routes with a common system of measurement is called a route system. Route systems usually define linear features with similar attributes. For example, a set of all bus routes in a county would be a route system. Many route systems can exist within a single cove

48、rage. For example, school bus, truck, and ambulance route systems could exist in a coverage of a city. Route systems are built using arcs, routes, and sections, and can accurately model linear features without having to modify the underlying arc-node topology. The route below is defined using four a

49、rcs. Notice how the routes endpoints fall along the arcs. Routes need not begin and end at nodes. Sections, as shown below, are the arcs or portions of arcs used to define each route. They form the infrastructure of the route system. The diagram below shows an example of attributes containing distan

50、ce measurements, such as milepost numbers or addresses, which can be used to locate events, such as accidents or pavement quality.,Dynamic segmentation,Dynamic segmentation (DynSeg) is the process of computing the map location (shape) of events stored in an event table.Dynamic segmentation is what allows multiple sets of attributes to be associated with any portion of a linear feature.,