Lecture2_GIS.pdf - Geodesy Map Projections and Coordinate Systems Geodesy the shape of the earth and definition of earth datums Map Projection the

# Lecture2_GIS.pdf - Geodesy Map Projections and Coordinate...

This preview shows page 1 - 14 out of 54 pages. Geodesy, Map Projections and Coordinate Systems Geodesy - the shape of the earth and definition of earth datums Map Projection - the transformation of a curved earth to a flat map Coordinate systems - (x,y) coordinate systems for map data Learning Objectives: By the end of this class you should know: the role of geodesy as a basis for earth datums how to calculate distances on a spherical earth the basic types of map projection the properties of common map projections the terminology of common coordinate systems how to use ArcGIS to convert between coordinate systems Spatial Reference = Datum + Projection + Coordinate system For consistent analysis the spatial reference of data sets should be the same. ArcGIS does projection on the fly so can display data with different spatial references properly if they are properly specified. ArcGIS terminology Define projection. Specify the projection for some data without changing the data. Project. Change the data from one projection to another. Types of Coordinate Systems (1) Global Cartesian coordinates (x,y,z) for the whole earth (2) Geographic coordinates ( f, l , z) (3) Projected coordinates (x, y, z) on a local area of the earth’s surface The z-coordinate in (1) and (3) is defined geometrically ; in (2) the z-coordinate is defined gravitationally N E W S (N, W) (S, W) (N, E) (S, E) Global Cartesian Coordinates (x,y,z) O X Z Y Greenwich Meridian Equator Geographic Coordinates ( f, l , z) Latitude ( f ) and Longitude ( l ) defined using an ellipsoid , an ellipse rotated about an axis Elevation (z) defined using geoid , a surface of constant gravitational potential Earth datums define standard values of the ellipsoid and geoid Latitude and Longitude Latitude - distance from the equator along the Y axis Longitude - distance from the prime meridian along the X axis. . Equator Latitude 0 o Latitude: ( 90 o N to 90 o S) Latitude 23½ o North Tropic of Cancer Latitude 23½ o South Tropic of Capricorn Longitude 30 o East Longitude 60 o East Longitude 30 o West Longitude 60 o West Positioning on the Earth s Surface East is the direction of rotation of the Earth North Pole South Pole 23½ o 23½ o 66½ o 90 o 90 0 21 st June 22 nd December 22 nd Sept 20 th March 30 o E 60 o E 90 90 o W 30 o 60 o Longitude 90 o East Longitude 90 o West Prime Meridian 0 o Longitude Longitude: (180 o E to 180 o W) Latitude and Longitude together enable the fixing of position on the Earth s surface. Geographical coordination system  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 