1. 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

2. Geospatial Science Teaching
Introduction through Advanced GIS
GIS Programming
Design of GIS Systems
Spatial Modeling
Modeling species movements in space and time
Environmental impacts

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

4. Chapter 3 Geodesy, Datums, Map Projections, and Coordinate Systems:
Ellipsoid
Geoid
Geographic coordinates:
latitude and longitude
Horizontal datums
Commonly used datums
Datum transformations

5. 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

6. 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.

7. USGS Benchmarks

8. USGS Benchmarks
Benchmark shapefiles by state:
Benchmark shapefiles by state:
Data Sheet:
Data date:
(N) (W)
Last “recovered” in 1962
GPS
DOP is accuracy
Repeat measurements for precision
Calibrate to:
USGS Benchmarks
NOAA, City of Arcata, NationalAltas.gov

9. Peak of Founder’s Hall Google Earth, 2012 DOQQ 1993
USGS Benchmark: NAD83
, or N, W

10. 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

11. Shape of the Earth
Eratosthenes (date)
6406km in radius
Today:
6,378km

12. 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 = (~21km)
Flattening Factor = (a-b)/a =
Inverse Flattening = a/(a-b) =

13. Flattening = Semi-Major Axis/ (Semi-Major Axis – Semi-Minor Axis)
Name
Semi-Major Axis
Inverse Flattening
WGS 84
WGS 72
298.26
NAD 27
NAD 83

15. GIS Fundamentals, Paul Bolstad, University of Minnesota

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

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

18. North-South Datum Shift

19. East-West Datum Shift

20. ArcGIS Datum Shifts
Picture of ArcGIS with geographic transform menu

21. Selecting a Datum Shift
Block on selecting transformation:
Article with tables to select datum shift for each version of ArcGIS:
SEER Web Site with EPSG Database:

22. Geographic/Datum Transforms
International Association of Oil and Gas Producers:
European Petroleum Survey Group (EPSG)
53 Ellipsoids
630 Datums (Ellipsoid plus prime meridian and units)

23. Geoid – Based on Gravity
Important because levels and plumbs used in field surveying had to be calibrated.
Exagerated Geoid – follows mean sea level
NOAA

24. Geoids vs. Ellipsoids
Spirit level used in traditional surveying follows the Geoid
Mean Sea level follows geoid
principles.ou.edu

25. Geoids Vs. Ellipsoids

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. Lines of Latitude Lines of Latitude Parallels 90º 67.5º 45º Equator
22.5º 0º
-22.5º
-45º
-67.5º
-90º

36. 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

37. Geographic Coordinates