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Introduction. Grew up in Northern California B.S. in Computer Science and Math from Chico 15 years with Hewlett-Packard CEO of tecBugs: GIS on the web Ph.D. from Colorado State University Research Scientist with the Natural Resource Ecology Laboratory
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Introduction • Grew up in Northern California • B.S. in Computer Science and Math from Chico • 15 years with Hewlett-Packard • CEO of tecBugs: GIS on the web • Ph.D. from Colorado State University • Research Scientist with the Natural Resource Ecology Laboratory • Visiting Professor at Oregon State University
Geospatial Science Teaching • Introduction through Advanced GIS • GIS Programming • Design of GIS Systems • Spatial Modeling • Modeling species movements in space and time • Environmental impacts
Forestry Wildlife Geology Fisheries Recreation Engineering Environmental Management Policy Restoration Education Engineering What are you interested in?
Chapter 3 • Geodesy, Datums, Map Projections, • and Coordinate Systems: • Ellipsoid • Geoid • Geographic coordinates: • latitude and longitude • Horizontal datums • Commonly used datums • Datum transformations
Geodesy • The science of measuring the shape of the Earth, and map projections, the transformation of coordinate locations from the Earth’s curved surface onto flat maps. NOAA NOAA NOAA
Coordinates • Must accurately and repeatedly locate spatial data on the earth • Problems: • The earth is not flat • The earth is not a perfect sphere • There are different versions of the earth’s shape • Measurements always have error Oldest known world map, 6th century BC Babylonia.
USGS Benchmarks • Benchmark shapefiles by state: http://www.ngs.noaa.gov/cgi-bin/sf_archive.prl http://fatwaramdani.wordpress.com NOAA, City of Arcata, NationalAltas.gov
Peak of Founder’s Hall • Google Earth, 2012 • DOQQ 1993 USGS Benchmark: NAD83 -124.07745, 40.87714 or 40 52 37.69549 N, 124 04 38.81922 W
The Earth is Not A Sphere! • Earth is like a big bag of molten lava spinning out its axis • Not Spherical, an “oblate spheroid” or “ellipsoid” 12, 756 km “Molten” 12, 714 km
Shape of the Earth Eratosthenes (date) 6406km in radius Today: 6,378km
Shape of the Ellipsoid • Circumference of the earth: • 40,075km • Radius at Equator, Semi-Major: • a=6,378,137.0 (~6,378km) • Radius at Poles, Semi-Minor: • b=6,356,752.3 (~6,356km) • Flattened at the poles by about: • Flattening = a-b = 21384.7 (~21km) • Flattening Factor = (a-b)/a = 0.00335270 • Inverse Flattening = a/(a-b) = 298.267
Major Axis Minor Axis Flattening = Semi-Major Axis/ (Semi-Major Axis – Semi-Minor Axis)
Datum • Horizontal Reference • Based on an ellipsoid (modern) • Includes: • Name: GCS_WGS_1984 • Spheroid: • Semi-Major Axis: 6378137.0 (Polar Radius) • Flattening: 298.257223563
Common Datums • NAD27 • NAD83 (1986) • NAD83 (HARN) • NAD83 (CORS96) • NAD83 (2007) • WGS72 • WGS84 (G1150) Up to 100 meter difference <2 meter differences
ArcGIS Datum Shifts • Picture of ArcGIS with geographic transform menu
Selecting a Datum Shift • Block on selecting transformation: • http://blogs.esri.com/esri/arcgis/2009/05/06/about-geographic-transformations-and-how-to-choose-the-right-one/ • Article with tables to select datum shift for each version of ArcGIS: • http://support.esri.com/en/knowledgebase/techarticles/detail/21327 • SEER Web Site with EPSG Database: • http://seer.science.oregonstate.edu
Geographic/Datum Transforms • International Association of Oil and Gas Producers: • European Petroleum Survey Group (EPSG) • http://www.epsg.org/ • 53 Ellipsoids • 630 Datums (Ellipsoid plus prime meridian and units)
Geoid – Based on Gravity Exagerated Geoid – follows mean sea level NOAA
Geoids vs. Ellipsoids Spirit level used in traditional surveying follows the Geoid Mean Sea level follows geoid principles.ou.edu
Vertical Datums • National Geodetic Vertical Datum of 1929 (NGVD 29). • Assumed water level is equal all along the coast, this created errors • North American Vertical Datum of 1988 (NAVD 88), more accurate, resulting in a difference of minus 1.51 feet • Vertical Datum Conversion Software VERTCON http://www.ngs.noaa.gov/datums/vertical/VerticalDatums.shtml
Spherical Coordinates • Longitude: • Degrees East or West from the prime meridian • Latitude: • Degrees North or South from the Equator Point of Interest Latitude Longitude
Longitude: -180° to 180° -180° 180° North Pole EAST WEST -90° 90° Prime Meridian 0° Polar View
Longitude: 180° W to 180° E 180° W 180° E Pole EAST 90° E WEST 90° W Prime Meridian 0° Polar View
Longitude: 0° to 360° 180° Pole EAST 90° 270° WEST Prime Meridian 360° 0° Polar View
Latitude: 90° to -90° 90° ~40° Equator 0° -90° Equatorial View
Latitude: 90°N to 90°S 90° N ~40°N Equator 0° 90° S Equatorial View
Lines of Longitude Lines of Longitude Meridians Prime Meridian Greenwich, England 0º 0º -45º 45º 67.5º -90º -67.5º 90º -22.5º 22.5º
Lines of Latitude Lines of Latitude Parallels 90º 67.5º 45º Equator 0º 22.5º 0º -22.5º -45º -67.5º -90º
Magnetic vs. Geographic • Magnetic North • Point at the north pole where compass needles point • Based on the earth’s magnetic field • Geographic North • Point that all modern maps use as north • Based on the rotation of the earth • There is also a magnetic south pole and geographic south pole