Cordinate system and map projection.pdf
- 1. Coordinate system and map projection prepared by Samuel Zewdu
- 2. Presentation out line Projection Coordinate system Geographic coordinate system Projection coordinate system UTM and UTM Zones Easting & Northing What is a Datum?
- 3. Projection: the method by which the curved 3-D surface of the earth is represented by X,Y coordinates on a 2-D flat map/screen. Distortion is inevitable Coordinate system A coordinate system is a method of defining how a file’s point locations display on a map. Different types of coordinate systems exist that control how the coordinates are shown on the map. The two main are:
- 4. Geographic Coordinate System use of Geographic latitude and longitude system, usually in Degree, Minutes and Seconds (DMS) Use spherical coordinates to specify locations on the surface of the earth When vertical locations (Elevation) are not concerned, Latitude/longitude pair are used Geographic coordinate systems are commonly called un projected lat/long
- 7. Projection: the method by which the curved 3-D surface of the earth is represented by X,Y coordinates on a 2-D flat map/screen. use of a known projection and datum. Linear cords (metres) are required in many occasions Distortions are inevitable with projection
- 8. 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
- 9. General rules for selecting a projection Tropical Country—cylindrical projection Temperate Country—conical projection Polar Regions—Azimuthal projection
- 14. UTM and UTM Zones Universal Transverse Mercator (UTM) System Developed in the late 1940s by the US Army the projection is the ‘Gauss-Kruger’ version of the Transverse Mercator- equidistant cylindrical projection
- 15. Intended for mapping areas : 840N – 800S Unit of measure is meter The world is divided into 60 zones of 60 of longitude in width (Fig. 2-4) Zone 1 starts at 1800 W and Each zone has its own coordinate system Universal Transverse Mercator (UTM) system is a specialized application of the Transverse Mercator projection.
- 16. It is not a single map projection. The globe is divided into 60 longitudinal zones (1-60), each spanning 6° of longitude or 6 degrees (800km) wide. Each zone has its own central meridian. Zones 1N and 1S start at 180° W The limits of each zone are 84° N and 80° S, with the division between north and south zones occurring at the equator.
- 17. There are also 20 longitudinal zones (8 degrees wide except zone X, 12o wide) denoted by letters C to X (Omitting letters I & O). The Polar Regions use the Universal Polar Stereographic coordinate system. Areas are referenced by quoting the longitudinal zone number followed by the latitudinal zone letter or the hemisphere e.g. points in Ethiopia, 37P, 37 N, 36P, 36N, etc (37N, 36N using hemispheres
- 20. What is a Datum? Every map projection and coordinate system begins with a precisely surveyed starting point The starting point and the network of points that extends from it is called the datum. e.g. for Adindan the starting point is in Sudan referenced to Clarke 1880 ellipsoid/spheroid
- 21. Using wrong datum can create an error of up to 200 or 300m on your map! Each datum has a name and often a date associated with it. e.g. Adindan, WGS 1984, etc
- 22. Each datum has a name and often a date associated with it. e.g. Adindan, WGS 1984, etc There are vertical and horizontal datum usually available on maps. e.g. Horizontal Datum: Adindan/ WGS 84 Vertical Datum: Mean Sea Level
- 23. Projection: UTM Spatial Reference: Ethiopia 1. DATUM = Adindan Ethiopia 2. PROJECTION = TM Clark 1880 3. COORDINATE SYSTEM = UTM 4. MAP UNITS = meter a. False easting = 500, 000 m b. Central Meridian = 39o East c. Scale factor = 0.9996
- 24. Easting & Northing Easting: UTM grid coordinates are always written or conveyed with the easting data string appearing first, before the northing data string By common convention, easting coordinates output from GPs units are typically followed by the letter "E" Vertical lines are measured from a separate point for each zone, namely, an imaginary line lying 500,000 meters west of the zone's central meridian