GIS Fundamentals. Mohamed M. Mostafa, GIS Department Manager - ITI ITI

Transcription

1 GIS Fundamentals Mohamed M. Mostafa, GIS Department Manager -

2 Introduction to GIS

3 CONTENTS Preface Definitions GIS Components Spatial Data Representation Data Types Spatial data Attribute Data GIS Framework And Capabilities Spatial Data Acquisition Spatial Data Modeling & Storage Spatial Data Queries Spatial Analysis Network Analysis

4 Preface DataBase (Modeling the World) Database Features and Relationships Spatial Aspect of DB

5 GIS DEFINTION a powerful set of tools for storing and retrieving as well, transforming & displaying spatial data from the real world for a particular set of purposes (Burrough, 1986) This definition uses non-scientific terms in describing the science as (powerful), (at well), (set of purposes), which of course couldn t define the technology accurately

6 GIS DEFINTION Another Definition of GIS: Automated system for the capture, storage, retrieval, analysis, and display of spatial data (Clarke, 1995)

7 Simply We can define Geographic Information System as (a computerized system that facilitates the phases of data entry, data analysis and data presentation especially in cases when we are dealing with geo-referenced data).

8 GIS COMPONENTS Software Hardware GIS Data People Methods

9 HARDWARE Data Input HW Data Processing/Storage HW Networking/Communication HW Data Output HW

10 SOFTWARE Desktop SW Professional SW Internet SW Extensions Stand alone developer SW

11 DATABASE Layers Data model Tables/relations Physical directories Meta data

12 PERSONNEL Qualifications Background Training Specialization Data entry operators Data conversion operators SW operators GIS specialists System analyst Programmers and Developers Project Managers

13 METHODS & APPLICATIONS System analysis System design System implementation Development / Programming Easy to use Less training Integrated to real work

14 Spatial Data Representation How can GIS organizes spatial data? GIS Represent the Real World In Abstract Form Layers

15 different types of data values nominal or categorical data values establish an identity (e.g. residential, institutional, industrial) ordinal data values can be put in natural sequence or order (e.g. population density categories low, medium, high) interval data natural sequence of values with equal intervals but with arbitrary zero point ratio data values have a natural zero point and allow for computation

16 What makes data spatial? Grid co-ordinate ordinate Placename Latitude / Longitude Description Postcode Distance & bearing Characteristics of spatial data: (Location, Geometry, Topology)

17 geographic fields (which have a value everywhere ) continuous fields changes in field values are gradual (e.g. elevation) discrete fields mutually exclusive bounded parts, all locations in one part have same field value (e.g. geological classes) step from continuous fields towards geographic objects (bounded, but assigns value for every location, not typical for objects)

18 a bit more on geographic objects normally do not study geographic objects in isolation collections of objects are viewed as a unit different objects do not occupy the (exact) same location collections objects can represent phenomena at higher aggregation level trees from forests parcels form blocks, districts and so forth roads from a road network

19 the notion of boundary relevant when shape and/or size matters (point features are exception) location, shape, size and orientation fully determined by the boundary of geographic object boundary can adequately represent geographic object crisp boundary boundary can be determined with precision degree of precision depends on data acquisition technique fuzzy boundary the area of transition is more of a continuum, not a discrete line e.g. coastline

20 DATA TYPES Spatial Data : is the kind of positional data that is related to earth s surface as a reference(positional Data) (describes geographic phenomena) Attribute Data : All information that are related to certain geographic feature.

21 Spatial Data Modeling Vector B B C C A B A Points Lines Polygons Raster

22 GIS Data Are Intelligent Because I know I am polygon #103, I am next to polygons 102, 104, 105 & 106, my area is 42.3 ha, I have low value for agriculture, high cut slope stability.etc I.D. Area (ha) Soil Type Ag Value Cut Slope Stability Erosivity Etc Nar LcT M L L H L H Zax Rnl H L ML ML MH MH Alb Nri ML Mh H L H L Rhi L ML ML Mjs Fak H Mh L H L H Graphics are linked to the Tabular Data That Describe What They Are

23 raster vs. vector model Raster model Vector model Simple data structure Easy and efficient overlaying Compatible with Remote Sensing imagery High spatial variability is efficiently represented Simple for programming by user Same grid cell definition for various attributes Inefficient use of computer storage Errors in perimeter and shape Difficult to perform network analysis Inefficient projection transformations Loss of information when using large pixel sizes Less accurate and less appealing map output Complex data structure Difficult to perform overlaying Not compatible with RS imagery Inefficient representation of high spatial variability Compact data structure Efficient encoding of topology Easy to perform network analysis Highly accurate map output

24 topological model The main elements of topology are the connectivity relationships between nodes, lines and polygons c B A D G F E Topological A inside B D connected to B C disjoint from B G overlaps E Proximal C near B D far from E Directional G east of C C north of D

25 Spatial relationships Everything is related to everything else

26 Building a GIS Building any geographic information system should take the following sequence: 1. Problem definition and user needs assessment 2. System analysis and conceptual design 3. Data collection 4. Data entry and editing 5. Data Modeling & Design 6. Data Manipulation and Processing 7. Data Display and Output (GUI)

27 Data Capturing

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29 Remote Sensing The Remote Sensing Process: 1. Energy Source or Illumination (A) 2. Radiation and the Atmosphere (B) 3. Interaction with the Target (C) 4. Recording of Energy by the Sensor (D) 5. Transmission, Reception, and Processing (E) 6. Interpretation and Analysis (F) 7. Application (G)

30 The Electromagnetic Spectrum The light which our eyes - our "remote sensors" - can detect is part of the visible spectrum The visible wavelengths cover a range from approximately 0.4 to 0.7 mm. The longest visible wavelength is red and the shortest is violet

31 Satellite Digital Images

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33 Survey costs Field Type Scale Imagery Cost (/km2) Agriculture Phenol. change 1:1,000,000 Landsat 80$ Forestry Forest mapping 1:250,000 Landsat 6$ Reg. Planning Feasibility Study 1:50,000 Spot SX 40$ Environment Risk zone 1:50,000 KFA $ mapping (5-12m) Topography Base map 1:10,000 aer. photo 2,000$ Cadastre Survey map 1:2,000 aer. photo 10,000$ Urban Planning Cadastre, utilities, topography 1:500 aer. photo 40,000$

34 Global Positioning System GPS The Global Positioning System (GPS) is formed from 24 satellites and their ground stations. GPS uses these man-made stars as reference points. The GPS is a passive system. GPS Elements: The Space Segment The Control Segment The User Segment Velocity * Time = Distance

35 1- Space Segment: The segment consists of the GPS satellite. These space vehicles (SVs) send radio signals from space 21 satellites with 3 operational spares 6 orbital planes, 55 Degree inclinations 20,200 kilometer,12 hours orbits

36 2- Control Segment: The Control Segment consists of a system of five tracking stations located around the world. (Hawaii, Ascension Island, Diego Garcia, Kwajalein, and Colorado Springs)

37 3- User Segment: The GPS User Segment consists of the GPS receivers and the user community.

38 Different GIS DATA SOURCES Field Survey: (Total stations Levels..) Photogrammetry Remote Sensing GPS Laser Systems Paper Maps Documents Files: (Auto Cad Sound Video Excel Multimedia) Videos and Images.

39 Introduction to GIS Lecture (2)

40 CONTENTS GIS Analysis Functions GIS Applications Geo Referencing Data

41 GIS Spatial Analysis Where is.? What is at? How does spatial pattern look for? What is near to / within? How many in? What if?

42 GIS Analysis Spatial Operations Format Conversion Geometric Transform. Object Generation Integrated Operations Measurement Operations Overlay Operations Neighborhood Operations Connectivity Operations Attribute Operations Attribute Editing Attribute Query

43 Operations on vector layers: Spatial Data Query (based on location or attributes) Ex: Areas < km2 and population > capita - point-in-polygon - line-line - polygon-polygon

44 GIS Analysis Deriving new information from existing data There are many types of geographic analysis. While this course cannot cover all of them, two common types of geographic analysis are described below. Proximity Analysis

45 overlaps : Polygon overlay A I II B III 4 5 layer 1 layer 2 overlay 1 A 2 B 1 I 2 II 3 III Output layer contains 1 A I 2 A II 3 B II 4 B I 5 B III all attributes from both input layers

46 Edge matching often required after appending data sets A C C A C B B B

47 Network Analysis Shortest Path Analysis

48 Nearest Location Analysis

49 Alternative Path Analysis

50 GIS APPLICATIONS ARCHIVING PLANNING MANAGEMENT DATA MINING Web and Mobile Applications

51 GIS APPLICATIONS ENVIRONMENTAL MANAGEMENT (Risk Assessment) (Environment Protection) (Disaster Control) HYDROLOGICAL APPLICATIONS (Water Resources Management Systems) (Water Quality Management Systems) (Flash Flood Control)

52 Change detection

53 GIS APPLICATIONS in Urban Planning

54 Areas of Services Analysis

55 GIS APPLICATIONS LAND RECORDS (Survey) (Taxes) (Legalisations) MASTER PLANNING (Site Selection) (Route Selection) (Services Allocation) (Slums Upgrading)

56 GIS APPLICATIONS SOCIO-ECONOMIC DEVELOPMENT MARKET ANALYSIS EMERGENCY APPLICATIONS (Police) (Health) (Fire Fighting) Others (Education Health Governmental - )

57 3D Analysis Cross Sections Sight Analysis Observer (tower) visible visible Not visible Not visible

58 GIS APPLICATIONS UTILITY MANAGEMENT (Network Operation & Management) (Planning) (Fault Control) TRANSPORTATION & LOGISTICS (Tracking) (Shortest Path) Natural Resource Management

59 Spatial Analysis Example: Finding Best Site that satisfies definite criteria Spatial analysis functions: Logic operations, arithmetic operations, geometric operations, statistical operations, map data retrieval and search, data inquiry, report generation, classification, reclassification, vector overlay, raster overlay, buffer zones, networking, streaming, DEM & DTM generation, generation of slopes and slope directions, hill shade generation, up stream and down stream determination, area and volume calculations, earth work, generation of profiles and cross sections, image analysis, and execution of internal or external mathematical models

60 Best Location

61 GIS in E-Government Delivering services (such as issuing building permits, payments and bills, licenses and IDs, voting, housing, university applications, etc.) to customers at their finger tips according to their taste and style with appropriate efficiency and allowing them to participate in the decision making process Thus, ICT is only a tool not an objective in it sown Customers: Citizens, Business men, Investors, Companies,

62 Citizensا Companies Investors Suppliers Service Centers Internet Networks Telephony Government Network Bawaba Firewalls (Ministries Special service needs Networks Standards Infrastructure Doc. Classification & Handling E-Payment Standards PKI National Database Security Specifications Application development E-Signature

63 Service Levels Information services. Inquiry services. Full transaction. Integration between agencies Push Vs Pull Interaction Personalization based on AI.

64 GII Geo-Information Infrastructure Information is an asset that can be shared and traded. It has value canbe sold; value can be added in various processing steps. This means that it needs to be transported, distributed and shared. For this, to be carried out effectively there is the need to set up an infrastructure for the efficient integration of information to enhance its accessibility and use.

65 National GII and different GIIs to support various stakeholders. GII for Urban Development GOPP + CAPMAS + Local Governorates GII for land and water management Ministry of Agriculture + MPWWR National GII Institutional and Economical issues: (Copyright, Privacy, Legal, Social, Policies, Organizational, Pricing, Cost-benefits ) Technical issues: (Standards, National Georeferencing, topographic template, administrative boundaries, geographic names, metadata, quality, updates,.) GII for land administration ESA + Deed Registration + Taxation GII for other applications

66 Data Output

67 Map Projection and Coordinate Systems Data in a GIS should refer to the correct location on the earth s surface

68 Shape of the Earth We think of the earth as a sphere It is actually a spheroid, slightly larger in radius at the equator than at the poles

69 Ellipsoid or Spheroid Rotate an ellipse around an axis Z b a O a Y X Rotational axis

70 Standard Ellipsoids Ellipsoid Major axis, a (m) Minor axis, b (m) Flattening ratio, f Clarke (1866) 6,378,206 6,356,584 1/ GRS80 6,378,137 6,356,752 1/ An earth datum is defined by an ellipse and an axis of rotation

71 Representations of the Earth Sea surface Mean Sea Level is a surface of constant gravitational potential called the Geoid Ellipsoid Earth surface Geoid

72 Definition of Elevation P Elevation Z z = z p z = 0 Land Surface Mean Sea level = Geoid Elevation is measured from the Geoid

73 Datums While the spheroid approximates the size and shape of the Earth, A datum is defined by the spheroid and that spheroid's position relative to the earth. A datum is a reference frame used to measure locations on the surface of the earth. It defines the origin and orientation of the lines of latitude and longitude (graticule). There are two types of datums: Earth-centered datum has its origin placed at the earth's currently known center of mass and is more accurate overall. Local datum is aligned so that it closely corresponds to the earth s surface for a particular area and can be more accurate for that particular area. Because datum's establish reference points to measure surface locations, they also enable us to calculate planar coordinate values when applying a projection to a particular area. Maps in the same projection, using different datums can have very different coordinates.

74 A local datum aligns its spheroid to closely fit the Earth s surface in a particular area, as illustrated in the diagram. A point on the surface of the spheroid is matched to a particular position on the surface of the Earth. This point is known as the origin point of the datum. The coordinates of the origin point are fixed and all other points are calculated from it.

75 Geoid: is the equipotential surface of the Earth's gravity field which best fits, in a least squares sense, global mean sea level

76 GPS height measurement The accuracy of GPS height measurements depends on several factors but the most crucial one is the "imperfection" of the earth's shape. Height can be measured in two ways. The GPS uses height (h) above the reference ellipsoid that approximates the earth's surface (shape). The traditional, orthometric height (H) is the height above an imaginary surface called the geoid, which is determined by the earth's gravity and approximated by MSL. The signed difference between the two heights the difference between the ellipsoid and geoid is the geoid height (N). The figure above shows the relationships between the different models and explains the reasons why the two hardly ever match spatially.

77 Coordinate systems Geographic: The most familiar locational reference system is the spherical coordinate system measured in latitude and longitude. Longitude and latitude are angles measured from the earth's center to a point on the earth's surface. Longitude lines, also called meridians, stretch between the north and south poles. Latitude lines, also called parallels, encircle the globe with parallel rings. Latitude and longitude are traditionally measured in degrees, minutes, and seconds (DMS). Longitude values range from 0 at the Prime Meridian (the meridian that passes through Greenwich, England) to 180 when traveling east and from 0 to 180 when traveling west from the Prime Meridian.

78 The geographical coordinate system. Geographical Coordinates Defining latitude & longitude

79 Coordinate systems Planar : Because it is difficult to make measurements in spherical coordinates, geographic data is projected into planar coordinate systems (often called Cartesian coordinates systems). On a flat surface, locations are identified by x,y coordinates on a grid, with the origin at the center of the grid. Each position has two values that reference it to that central location; one specifies its horizontal position and the other its vertical position. These two values are called the x- coordinate and the y-coordinate.

80 Coordinate systems X - Y + X - Y - Y Data X + Y + usually here X + Y - X Spherical coordinate system Three-dimensional Latitude and longitude are not uniform across the earth s surface Cartesian coordinate system Two-dimensional Measures of length and angle are uniform

81 Map Projections What is map projections? The earth appears to be a sphere but, in fact, it is slightly flattened at the poles compared to the equator, so the earth is a spheroid or ellipsoid in shape. To be presented on a map, the earth's threedimensional features are depicted as flat representations through a mathematical conversion. This is commonly referred to as a map projection.

82 Map Projection Classification Class Azimuthal Cylindrical Conical.. tangent or secant. Aspect Normal Oblique Transverse Property Equivalent equal area Equidistant Conformal shapes and angles preserved

83 Projections Preserve Some Earth Properties Area - correct earth surface area (Albers Equal Area) important for mass balances Shape - local angles are shown correctly (Lambert Conformal Conic) Direction - all directions are shown correctly relative to the center (Lambert Azimuthal Equal Area) Distance - preserved along particular lines Some projections preserve two properties

84 Projections Classes Each of these basic types can have several variations. For example, the projection surface can simply wrap around the globe, resulting in a tangent where distortion is minimized, or it can intersect the globe, resulting in two secants, between which the distortion is minimized

85 Projection onto a Flat Surface

86 Azimuthal Projection

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88 Cylindrical equal-area projection (normal aspect)

89 Cylindrical equidistant projection (normal aspect)

90 Mercator's cylindrical conformal projection (normal aspect)

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92 Choice of a map projection Position of the area Aspect (tangent or secant) Shapes of the area Rectangle area (cylindrical) Triangle (conical) Circular (azimuthal) Size of the area Small (azimuthal, tangent) Large (conical, cylindrical, secant) Purpose of the map

93 Map Projection Parameters Projected coordinate systems must have defined projection parameters. Parameters specify the data-point origins and customize projections to the area of interest. There are two categories of parameters. Linear parameters use projected coordinate system units like false eastings, false northings, and scale factors. Angular parameters use geographic coordinate system units like azimuths, central meridians, central parallels, longitudes and latitudes of origin, center, and standard parallels 1 and 2. These parameters allow the mapmaker to manipulate projections and their distortions. The shape and size of a geographic coordinate system s surface is defined by a sphere or spheroid. According to map scale. Rotating the ellipse around the semiminor axis creates a spheroid.

94 Map Projection Parameters Following are definitions and discussion of projection parameters required by various projections. Semi-Major Axis of Ellipsoid This defines the size of the Earth by the radius at its widest part. The value measured by Clarke in 1866, 6,378,206 m. Semi-Minor Axis of Ellipsoid This is the Earth s radius at its narrowest part. Clarke s value of 6,356,584 meters is the default. Standard Parallel For conic projections, the standard parallel refers to the one or two lines of latitude along which the cone contacts the Earth. Central Meridian For conic projections, the central meridian is the single line of longitude that is truly vertical on the map. It is usually in the middle of the map. Legends for maps should always include the coordinates for the standard parallels and the central meridian.

95 Map Projection Parameters False Easting Many projections have an origin point. For example, the origin might be located at the intersection of the central meridian and the standard parallel or at the central meridian and the latitude of the projection s origin. The origin point is particular to each projection. The false easting is the x- coordinate value assigned relative to this origin. For instance, if the origin of the projection (in latitude-longitude) is in the center of the map, all areas to the west of the origin would be negative if a false easting of zero is assigned. To make the x-coordinates positive for the entire map, set the false easting to a positive number. False Northing This is similar to false easting except that it is an arbitrary y-shift. Using the example above where the projection s origin was in the center of the map, everything to the south would be negative unless a positive false northing was assigned. False easting and northing must be in meters (i.e., the same units as the spheroid).

96 Map Projection Parameters Latitude of Projection s Origin For conic projections with two standard parallels, to know where to put a false easting or northing because there are two lines of latitude defining the projection. The latitude of the projection s origin identifies where to put this origin. Scale Factor The degree of reduction or enlargement necessary to fit a curved Earth onto a flat projection surface. Because the curved surface of the Earth is longer than the surface onto which it is projected, features must be reduced in scale relative to the point of true scale. The default value is 1.0. How to predict the (Scale) it in digital maps??

97 Geometric transformation Data necessary for spatial analysis or map production could be found in different projections (rather than different scales).

98 Geometric Transformation Geometrical transformation is a solution processed to integrate the geometric components of different data sets. Types of geometric transformation : Affine transformation (To apply the transformation, one needs at least three corresponding points in the old and new data sets) Curvilinear (rubber-sheeting) transformation (The two data sets do not geometrically match & One of the data sets is of an unknown characteristics)

99 Affine transformation Affine transformation converts all the coordinates of a specific data set into the coordinates of another coordinate system The transformation could Be done mathematically using the formula X = Ax+ By + C Y = Dx + Ey + F Where X Y are coordinates in the new system. A, B, C, D, E, & F are parameters defined by comparing both points in the 2 data sets.

100 The projection transformation is a combination of three basic operation: 1. Rotation 2. Translation 3. scaling

101 Curvilinear transformation Why using curvilinear transformation? The two data sets do not geometrically match One of the data sets is of an unknown characteristics Curvilinear transformation is also known as rubbersheeting transformation, which is a less accurate type of transformation, so one should only apply it when there are no alternatives. The starting point in this process is a data set geometrically correct for the purpose it is needed for, the other data set characteristics is less well known. (example: unknown map projection or map distortion)

102 How can we perform curvilinear transformation? Rubber sheeting transformation is done by three simple steps: 1. Clearly identify corresponding points in the two data sets 2. Linking the corresponding points by a vector 3. Pull and push the less known data set points till all vectors are reduced to zero Note: not all points are affected by the same degree, as in the affine transformation

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105 scale and resolution map scale ratio between distance on a paper map and distance on the same stretch in the terrain large-scale: much detail small-scale: fewer detail digital spatial data essentially without scale!!!!!!!! further elaborated in later lecture resolution commonly associated with cell size of tesselation

106 Map Scale Equation for computing map scale where Sm stands for the scale of the map, Dm stands for a distance measured on the map, and Dg stands for a corresponding distance on the ground, Equation for computing the average scale of an aerial photograph where Sp stands for the average scale of the photo, f stands for the focal length of the camera used to take the photo, and H is the flying height of the aircraft carrying the camera above the average elevation of the terrain. Map scale could be represented with graphics.

107 Map Scale and Accuracy Accuracy is scale dependent. The U. S. Geological Survey's National Map Accuracy Standard guarantees that the mapped positions of 90 percent of well-defined points (such as benchmarks, road intersections, and such) shown on its topographic map series will be within 0.02 inches of their actual positions on the map. Obviously, 0.02 inches (0.508 millimeters) on the map represents a greater or lesser distance on the ground depending on the scale of the map. The allowable error of well-defined points at 1:100,000 scale is 1 / 100,000 = mm / Dg, or Dg = mm * 100,000 = 50,800 mm or 50.8 meters. By comparison, the allowable error on 1:250,000 scale maps is a whopping 127 meters.

108 Example: UTM Universal Transverse Mercator UTM - cylindrical projection with a central meridian that is specific to a standard UTM zone. There are 60 zones around the world (each zone 6 degree). Coordinates are usually measured in meters from the central meridian (x) and the equator (y). Minimal distortions of area, angles distance and shape at large and medium scales. Very popular for medium scale mapping. Parameters required for projecting a map: latitude of origin central longitude (meridian) spheroid/datum false easting/northing (., an offset to avoid negative numbers) map units always record all information included on a map sheet

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110 UTM graticule Northern Hemisphere Equator Central meridian Parallels and meridians intersect at right angles (conformal projection) Southern Hemisphere

111 UTM graticule and grid Northern Hemisphere Equator Central meridian m E m E Southern Hemisphere m m m 0 m North m North m E m E 3º 2º 1º 0º 3º 2º 1º 0º

112 UTM graticule and grid Northern Hemisphere 3º 2º m E m E m E m E m m Equator 1º 0º 3º 2º 1º m 0 m North m North 0º Southern Hemisphere Central meridian graticule projection

113 Spatial Data Visualization (map design): Dot Density Maps

114 Introduction to GIS Lecture (2)

115 CONTENTS GIS Applications GIServices for E-Gov Geo-spatial Information Infrastructure (GII)