Introduction to Geoinformatics L-3. Georeferencing Dr. György SZABÓ associate professor Budapest University of Technology and Economy Department of Photogrammetry and Geoinformatics gyszabo@eik.bme.hu

Contents OVERVIEW Discuss the necessity of commonly used systems, including place names and street addresses, 2D, 3D coordinates, linear referencing, GSM, conversion between different georeferencing systems LEARNING OBJECTIVES Know the requirements for an effective system of georeferencing; Be familiar with the problems associated with placenames, street addresses, and other systems used every day by humans; Know how the Earth is measured and modeled for the purposes of positioning; Know the basic principles of map projections, and the details of some commonly used projections; Know about conversion between different systems of georeferencing Longley, Goodchild, Maguire, Rhind (2011): Geographical Information Systems and Science CH – 5. pp. 123-146.

How can we manage the complexity of our environment?

Georefrences and Coordinate Systems Necessity of common system Contionous georeferencing Relative georeferencing Polar coordinates, Offset, Linear ref. Direct georeferencing Datums Map projections Coordinate systems Elevation referencing Discrete georeferencing Adresses, postal codes, Grids, Zones, GSM Cell

Importance of Georeference Dissimilar geographic data in one GIS project Different conceptual, logical, geometrical representation Traditionally different description of real world ->Necessity of common system

Properties of the Reference Systems Precision Surveying: no angular and area, limited linear distorsion 1/10000, sub-dm accuracy Topography: limited angular, area and linear distorsion ~ m accuracy Geography/bussiness: importance of visualisation not accuracy Dimensions 1D : elevation reference, local vetical observations 2D : planar and sphere/ellipsoidal surface observations 3D : real 3d geocentral observations Principal methods Continouos (Direct, Relative) georeferencing / to access every point in the reference system Discrete georeferencing / to access discrete zone with limited positional accuracy

Discrete georeferencing Position of phenomena are measured relative to a fix, limited surface of the Earth: Adresses, street codes Cadastral parcel ID Postal codes, Geographic names Administrativ zones, statistical units Grids, Map sheets (quad-tree) GSM Cell, WIFI Zone, IP address Geocoding: connection between the Direct and Discrete systems

General city postal address situation

International examples Your home country?

Hungary / BME Library 1111 Budapest Műegyetem rkp.3. Hungary Budapest Bertalan Lajos u. 1-3. H-1111, Hungary 1111 Budapest Budafoki u. 4-6. Magyarország

Relationships between UPU postal address components

Rural situation (no street names)

Discrete georeferencing samples DIGI TV coverage zones Bank Office zones and account distribution

The location of a GSM user – LBS services

Contionous georeferencing -> Continous measurement of position of phenomena in relation to a refference point Relative (indirect) georeferencing: Polar coordinates Offset distance Linear measurement along networks (road, river) Direct georeferencing of points, lines, areas: Coordinates on the curved surface of the Earth (2D) Geocentric coordinates (3D) Rectangular coordinates (2D) Vertical coordinates, elevations (1D)

Relative (indirect) georeferencing Practical on-site referencing Polar coordinates Offset distance Linear measurement along networks (road, river)

Direct Georeferencing Components: Datum, Map projection, Coordinate system Datum: modell, reference level of the Earth used for geodetic calculations Map projection: projected the curved surface of the Earth to plane surface Coordinate system: a reference systems to serve the geometrical computations

Datum – Earth modells Plan Sphere Geoid Ellipsoid II. century Bc. XVII. century Ac. XIX. century Ac. Plan Sphere Geoid Ellipsoid

Ellipsoid Definitions Name Year Half big-axis (m) Flatness =(a-b)/a Walbeck 1819 6 376 896 1/302.78 Bessel 1837 6 377 397.15 1/299.1518 Hayford 1924 6 378 388 1/297 Kraszovszkij 1940 6 378 245 1/298.3 IUGG 67 1967 6 378 160 1/298.247 167 WGS 84 1984 6 378 137 1/298.257 223 563 ETRS 1989 1/298.257 222 101

Coordinate Systems Geocentral P(x,y,z) Ellipsoidal P(lat, long) Plan X = f1(Ф,Λ) Y = f2(Ф,Λ) Y N N X Geocentral P(x,y,z) Ellipsoidal P(lat, long) Plan P(x, y)

The basis for three types of map projections—cylindrical, planar/azimutal, and conic. In each case a sheet of paper is wrapped around the Earth, and positions of objects on the Earth’s surface are projected onto the paper. The cylindrical projection is shown in the tangent case, with the paper touching the surface, but the planar and conic projections are shown in the secant case, where the paper cuts into the surface. (Reproduced by permission of Peter H. Dana)

Examples of some common map projections Examples of some common map projections. The Mercator projection is a tangent cylindrical type, shown here in its familiar equatorial aspect (cylinder wrapped around the equator). The Lambert Conformal Conic projection is a secant conic type. In this instance, the cone onto which the surface was projected intersected the Earth along two lines of latitude: 20 North and 60 North. (Reproduced by permission of Peter H. Dana)

(A) The so-called unprojected or Plate Carrée projection, a tangent cylindrical projection formed by using longitude as x and latitude as y. (B) A comparison of three familiar projections of the United States. The Lambert Conformal Conic is the one most often encountered when the United States is projected alone and is the only one of the three to curve the parallels of latitude, including the northern border on the 49th Parallel. (Reproduced by permission of Peter H. Dana)

The UTM (Universal Transver Mercator) projection

The system of zones of the Universal Transverse Mercator system The system of zones of the Universal Transverse Mercator system. The zones are identified at the top. Each zone is six degrees of longitude in width (Reproduced by permission of Peter H. Dana)

Major features of UTM Zone 14 (from 102 W to 96 W) Major features of UTM Zone 14 (from 102 W to 96 W). The central meridian is at 99 W. Scale factors vary from 0.9996 at the central meridian to 1.0004 at the zone boundaries. See text for details of the coordinate system. (Reproduced by permission of Peter H. Dana)

Elevation referencing Geoid: mean see level, at the same level of the gravitational potential GPS -> P(x,y, ellipsoid height) !!! Earth surface H: geoid height h: ellipsoid height n: Geoid undulation h=H-n Geoid Ellipsoid

Direct reference system: Map Discrete reference: adresses Geocoding/Geotagging Direct reference system: Map Bussiness Analysis Geocoding Discrete reference: adresses

Georegistration: transformation between Planimetric Systems Helmert – 4 parameter: x = a0 + a1 x’ – a2 y’ y = b0 + a1 y’ + a2 x’ Affin – 6 parameter: x = a0 + a1 x’ + a2 y’ y = b0 + b1 x’ + b2 y’.

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