The Questions are on the last slide. Also it was to be answered in full sentences. At least 2-3sentences
Chapter2_WhereInTheGeospatialWorldAreYou? Chapter 2 Basic Mapping Processes Introduction I. Defining an Object’s Location in the World II. Geographical Coordinate System III. What is the Earth’s Shape? IV. Impact of Earth’s Shape on Location Determination V. A Datum as a Mapping Framework I. Horizontal Datum II. Vertical Datum How do we define the location of an object in the world? 40.625106o, -73.961446o 40o 37’ 30.3816”, -73o 57’ 41.2056” 40.606789o, -74.044016o 40o 36’ 24.4404”, -74o 2’ 38.4576” Chapter 2 Basic Mapping Processes Geographical Coordinate System Chapter 2 Basic Mapping Processes Types of Coordinate Systems Geographical Coordinate System (Spherical Coordinates) Projected Coordinate System (Cartesian Coordinates) Chapter 2 Basic Mapping Processes source: http://courses.washington.edu What differences do you see between these? Types of Coordinate Systems Projected Coordinate System (Cartesian Coordinates) Chapter 2 Basic Mapping Processes source: http://courses.washington.edu Geographic Coordinate System Source: Extracted from PDF version of the http://www.disam.dsca.mil/pubs/archives.htm Vol 26-4 2004 DISAM Journal Graticule The pattern of meridians and parallels on the earth. Great Circle A circle that divides the earth into two equal halves. Small Circle A circle that divides the earth into two unequal halves. Chapter 2 Basic Mapping Processes Latitude is the angular distance north or south of the equator. Geographic Coordinate System Image Source: Christopherson, Geosystems 6th edition Parallels connect points of equal latitude. Meridians connect points of equal longitude. Longitude is the angular distance east or west of the Prime Meridian. Chapter 2 Basic Mapping Processes Geographic Coordinate System A degree of latitude or longitude can be subdivided further into minutes and seconds… One degree is divided into 60 minutes (60’)… One minute is divided into 60 seconds (60”)…. Example: 44o42’06”E This reads 44 degrees, 42 minutes, 6 seconds East of the Prime Meridian. 44th degree divided into 60 minutes 42nd minute divided into 60 seconds 42nd minute of 44th degree 6th second of 42nd minute 44oE 45oE 44o43’E44o42’E So, how do you convert between DMS and Decimal Degrees? Chapter 2 Basic Mapping Processes What is the Earth’s Shape? Chapter 2 Basic Mapping Processes Chapter 2 Basic Mapping Processes Three Important Shapes of the Earth “Good Enough” For General Mapping Purposes Need to Consider Both in Detailed Mapping Efforts Impact of the Earth’s Shape on Location Determination Chapter 2 Basic Mapping Processes An accurate and precise calculation of “the vertical” is required in order to accurately calculate a locations’ latitude and longitude using traditional methods. Deflection of the vertical – the difference between a vertical line passing through the earth’s center of gravity (geoid) and a vertical line passing through the earth’s geometric center (ellipsoid). Chapter 2 Basic Mapping Processes Impact of Earth’s Shape on Latitude / Longitude Determination What About a Point’s Elevation Value? Different elevation values are obtained based on which shape is used. Which surface do you use? Chapter 2 Basic Mapping Processes Horizontal Datum Chapter 2 Horizontal Datum Horizontal Datums Local Horiz. Datum – ellipsoid is constructed as a best fit with the geoid in a specific area. Global Horiz. Datum - ellipsoid is constructed as a best fit with the geoid globally Source: http://www.kartografie.nl/geometrics/Reference%20surfaces/body.htm Chapter 2 Horizontal Datum A Selection of Ellipsoids Used for Mapping Purposes Name Date Equatorial Radius (m) Polar Radius (m) Area of Use WGS84 1984 6,378,137 6,356,752.31 Worldwide GRS 80 1980 6,378,137 6,356,752.3 Worldwide (Nad83) Australia 1965 6,378,160 6,356,774.7 Australia Clarke 1880 1880 6,378,249.1 6,356,514.9 France, most Africa Clarke 1866 1866 6,378,206.4 6,356,583.8 North America (Nad27) Airy 1849 6,377,563.4 6,356,256.9 Great Britain Chapter 2 Horizontal Datum North American Datum of 1927 (NAD27) Meades Ranch-Center of the Contiguous US The base point was the reference point for almost all land survey measurements in the United States from 1927 until the establishment of the North American Datum of 1983 (NAD 83) and the World Geodetic System of 1984 (WGS84). Chapter 2 Horizontal Datum Effect of the Datum Change The North American Datum of 1983, contains fewer inherent local distortions than the North American Datum of 1927 The datum change resulted in the adjustment (0-250 meters) of most latitude and longitude locations throughout the North America. Chapter 2 Horizontal Datum Chapter 2 Vertical Datum Vertical Datum Chapter 2 Vertical Datum Vertical Datums and Elevation Measurements Traditionally, vertical measurements are referenced to a local vertical datum that has a starting point at a tidal station. North American Vertical Datum of 1988 Many elevation measurements in North America are tied to the North American Vertical Datum of 1988 (NAVD 88) The zero surface for this datum is defined by Mean Sea Level at the Rimouski tidal station in Canada Mean Sea Level (MSL) is defined by surveyors as the average of all low and high tides at a particular starting location over a 19 (18.6) year lunar period called Metonic cycle. Chapter 2 Vertical Datum Vertical Datums and Elevation Measurements A local vertical datum is implemented through a vertical control network. Example: Geodetic leveling in the Netherlands using the vertical datum defined by the Amsterdam tidal station Source: http://www.kartografie.nl/geometrics/Reference%20surfaces/body.htm Chapter 2 Vertical DatumNO CLASS - Classes Follow MONDAY Schedule Important Dates! Added to the Calendar on Blackboard: Tuesday Feb 7th (that’s today) - last day to drop with 50% refund Tuesday Feb 14th (one week from today) - last day to drop with 25% refund and not receive a “W” Tuesday Feb 21st - Classes follow the Monday schedule - No Class Meeting Thursday Feb 23rd - I will be traveling, I will pre-record and send out a lecture, I will be available via email for questions during our class time (up until the plane takes off) After that, no schedule disruptions until SPRING BREAK The UTM Zones Chapter 2 Coordinate Systems Grid Systems: UTM 840N 800S 00 There are total 60 North-South Zones, starting from 180ºW and each being 6º wide in longitude 1800W 1800W 1800E 1800E 00 00 00 Chapter 2 Coordinate Systems Grid Systems: UTM NAD_1983_UTM_Zone_17N Projection: Transverse_Mercator False_Easting: 500000.000000 False_Northing: 0.000000 NAD_1983_UTM_Zone_18N Projection: Transverse_Mercator False_Easting: 500000.000000 False_Northing: 0.000000 Two UTM zones for New York But what’s the deal with this falseness? Chapter 2 Coordinate Systems Grid Systems: UTM source: http://www.vidiani.com Let’s use Manhattan as a model UTM does not use use negative numbers. UTM North zones doesn’t use false northing, it uses the equator (black line) UTM Southzones, rather than measuring south from the equator (negative numbers) instead it measures up from an imaginary false north (red line) 500k UTM Meridian UTM Meridian False Easting Transverse Mercator Projection Used for North – South trending states Used for East – West trending states Lambert Conformal Conic Projection Chapter 2 Coordinate Systems Grid Systems: UTM Chapter 2 Coordinate Systems Grid Systems: UTM State Plane Systems • Lambert Conformal Conic • Transverse Mercator • Oblique Mercator (Alaska) NAD_1983_StatePlane_New_York_West Projection: Transverse_Mercator False_Easting: 350000.000000 False_Northing: 0.000000 Chapter 2 Coordinate Systems Grid Systems: UTM • A systematic rendering of a graticule of lines of latitude and longitude on a flat sheet of paper. • A mathematic transformation of the curved earth surface to a flat sheet of paper Curved Earth Geographic coordinates (Latitude & Longitude) Flat Map Cartesian coordinates: x,y (Easting & Northing) A Map Projection is … Chapter 2 Map Projections What is a map projection? Maps can’t or don’t show the whole world • Examples: – Mercator: usually extends to 80o N and 80o S – Gnomonic, limited mathematically to cover less than a hemisphere. Although maps are useful, they have limitations… Chapter 2 Map Projections 0 60E 90E 30E 30N 60W 30 W 90W 18 0E 15 0E 120 E 18 0W 120W 150W 60N 15 0N What is a map projection? 18 00 W 18 00 W 180 0W 900N Point to Point Point to line Continuity Loss Breaks in continuity (where the same line forms two edges of the map) (World Miller Cylindrical Projection)(World from space, modified) Correspondence and continuity are lost and geographic distortions occur. Chapter 2 Map Projections Although maps are useful, they have limitations… What is a map projection? ConeCylinder Plane (Azimuthal) Developable Surface of Map Projection Chapter 2 Map Projections Creation of a Map Projection Choose based on scale, place, other considerations Plane Projection Orientations Normal (Polar) Transverse (Equatorial) Oblique Chapter 2 Map Projections Creation of a Map Projection Cylindrical Projection Orientations Transverse (Along a Meridian) Oblique Normal (Equatorial) Chapter 2 Map Projections Creation of a Map Projection Light source at the center of the earth Light source at the infinite distance Light source sits exactly opposite the developable surface’s point of tangency Gnomonic Projection Orthographic Projection Stereographic Projection Chapter 2 Map Projections Creation of a Map Projection Light Type for Map Projections • Two Major Properties Properties that can exist at all points on certain projections. Earth Properties to Preserve or Distort • Two Minor Properties Properties that can exist in relation to only one or two points or lines on certain projections. 12 1 2 12 12 5 0 ° 5 0 ° 4 0 ° –Conformality: Shape (Angle) –Equivalence: Area (Size) –Distance (Scale) –Direction (Azimuth) Chapter 2 Map Projections S.A.DDEarth’s Properties Mercator Conformal Projection Generating Globe Chapter 2 Map Projections Conformality (Shape)Earth’s Properties Lambert’s Conic Conformal ProjectionAnother Example: Example of a Conformal Projection - preserves shape Mollweide Equal-area Projection Chapter 2 Map Projections Equivalence (Area)Earth’s Properties Sinusoidal Projection Albert’s Conic Equal-Area Projection Lambert’s Azimuthal Equal Area Other Examples: Generating Globe Example of an Equal-Area Projection - preserves area • Conformality (Shape) and Equivalence (Area) are mutually exclusive, you CANNOT preserve both on one map. • However, a map can be both azimuthal (preserving direction) and equivalent (preserving area) or both azimuthal and equidistant (preserving scale). Azimuthal equidistant projection Azimuthal equal-area projection Chapter 2 Map Projections S.A.D.D.Earth’s Properties Compromise projections are projections that do not preserve any of the globe properties but also does not result in extreme distortion of any property. • It is impossible and unnecessary to keep all or none of the properties precisely. • Compromise projections have better visual effects as used for the education purpose. • Commonly used ones include Miller Cylindrical, Robinson, and Winkel Tripel. Chapter 2 Map Projections Compromise ProjectionsEarth’s Properties Chapter 2 Map Projections Compromise ProjectionsEarth’s Properties Projection Selections • Purpose of the map Are aesthetics important? Are density calculations being made? Are distance and / or direction calculations being made? • Size of the area being mapped Is an entire continent being mapped? f • Shape of the area being mapped Does the area being mapped have a “skinny” shape? (e.g. Chile) Does the area being mapped have a rectangular shape? (e.g. United States) • Latitudinal location of the area being mapped Polar Location? Mid-Latitude Location? Equatorial Location? What considerations do we need to make when selecting a map projection? Great Website: http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html