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

What are you interested in? Forestry Wildlife Geology Fisheries Recreation Engineering Environmental Management Policy Restoration Education Engineering

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

USGS Benchmarks Benchmark shapefiles by state: http://www.ngs.noaa.gov/cgi-bin/sf_archive.prl http://www.ngs.noaa.gov/GEOID/GPSonBM96/gpsbms.html Benchmark shapefiles by state: http://www.ngs.noaa.gov/cgi-bin/sf_archive.prl Data Sheet: http://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=LV0687 Data date: 20121222 40 52 37.69549(N) 124 04 38.81922(W) Last “recovered” in 1962 GPS DOP is accuracy Repeat measurements for precision Calibrate to: USGS Benchmarks 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

Flattening = Semi-Major Axis/ (Semi-Major Axis – Semi-Minor Axis) Name Semi-Major Axis Inverse Flattening WGS 84 6378137.0 298.257223563 WGS 72 6378135.0 298.26 NAD 27 6378206.4 294.9786982 NAD 83 298.257222101

GIS Fundamentals, Paul Bolstad, University of Minnesota

Datum Horizontal Reference Includes: Based on an ellipsoid (modern) Name: GCS_WGS_1984 Spheroid: Semi-Major Axis: 6378137.0 (Polar Radius) Flattening: 298.257223563

Common Datums NAD27 NAD83 (1986) NAD83 (HARN) NAD83 (CORS96) WGS72 WGS84 (G1150) Up to 100 meter difference <2 meter differences

North-South Datum Shift

East-West Datum Shift

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 Important because levels and plumbs used in field surveying had to be calibrated. 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

Geoids Vs. Ellipsoids

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 Used in coastal and estuary work 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 When we describe the earth in spherical coordinates it is called Geographic or Un-projected The lines running north to south are called lines of longitude The lines running east to west are called lines of latitude As we move east-west we change through 360 degrees. In other words, the earth is 360 degrees around As we move north-south we chagne through 180 degrees. In other words, going from the north pole to the south pole is 180 degrees Longitude

Longitude: -180° to 180° EAST WEST -180° 180° North Pole -90° 90° 0° - The system we will work with the most encodes longitude from -180 in the middle of the pacific to 0 degrees at the Prime Meridian which runs through Greenwich England and back to 180 degrees in the middle of the Pacific. Prime Meridian 0° Polar View

Longitude: 180° W to 180° E EAST WEST 180° W 180° E Pole 90° E 90° W - Another common and older way of encoding longitude is from 180 degrees West to 180 degrees East Prime Meridian 0° Polar View

Longitude: 0° to 360° EAST WEST 180° Pole 90° 270° 360° 0° Polar View Prime Meridian - A rare encoding is to go from 0 degrees at the Prime Meridian through to 360 degrees 360° 0° Polar View

Latitude: 90° to -90° ~40° 90° Equator 0° -90° Equatorial View - A rare encoding is to go from 0 degrees at the Prime Meridian through to 360 degrees -90° Equatorial View

Latitude: 90°N to 90°S ~40°N 90° N Equator 0° 90° S Equatorial View - A rare encoding is to go from 0 degrees at the Prime Meridian through to 360 degrees 90° S Equatorial View

Lines of Longitude Lines of Longitude Meridians Prime Meridian Greenwich, England 0º -90º -67.5º -45º -22.5º 0º 22.5º 45º 67.5º 90º

Lines of Latitude Lines of Latitude Parallels 90º 67.5º 45º Equator 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

Geographic Coordinates