Control Surveys and Coordinate Systems The Earth…… is Round Basic Shape of the Earth: Oblate Spheroid of Revolution The length of the equatorial axis is approximately 27 miles greater than the polar axis. Average value of the Earth’s radius: 20,906,000 ft GEODESY…..
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Control Surveys and Coordinate Systems · State Plane Coordinate System. Lambert Conformal Conic Projection 34-20 N. 36-25 N. False Easting. ... Grid coordinate ÷ grid factor = “ground
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Control Surveys and Coordinate Systems
The Earth…… is RoundBasic Shape of the Earth: Oblate Spheroid of Revolution
The length of the equatorial axis is approximately 27 miles greater than the polar axis.
Average value of the Earth’s radius: 20,906,000 ft
GEODESY…..
Control Surveys and Coordinate Systems
HorizontalLattitude (φ): 0° is the Equator. Increases to 90oN and 90oS at the north and south poles.
Longitude (λ): 0° is the Prime Meridian and runs through Greenwich England. These values increase to 180oE and W.
VerticalMean Sea Level-Geodesists commonly call this surface the “geoid”
- The geoid is a surface which is everywhere perpendicular to the plumb line (vertical or direction of gravity)
The Vertical Reference
The Horizontal Reference
• The first Major adjustment in control Data was made in 1927 Resulting in the North American Datum of 1927; (NAD 27)
– The Reference Ellipsoid used was Clarke’s Spheroid of 1866• Semimajor Axis: 6,378,206.4 m• Semiminor Axis: 6,356,583.8 m
• The North American Datum of 1983 (NAD 83)– The Reference Ellipsoid used was GRS80
• Semimajor Axis 6,378,137.0 m• Semiminor Axis 6,356,752.3 m
– Covers the North American Continent, Greenland, parts of Central America– Geographic point in this system is latitude and longitude.
• Too cumbersome for everyday surveying (State Plane Grid) , Used in Control Surveys (GPS)
• Angles, seconds MUST be carried out to at least the 4th decimal place for – Accuracies between NAD 83 1st-order stations are better than 1:200,000-this is due to
GPS.
GRS80 Ellipsoid
NAD27
WGS84 and NAD83 share the GRS80 ellipsoid but the origin differs by about 2mNAD27 uses the Clark spheroid of 1866, the origin is 236 m from WGS84
NAD83
GEOID
Earth MassCenter
Approximately236 meters
Approximately2 meters
NAD27, NAD83, WGS84
WGS84
Principal Vertical Datums
• National Geodetic Vertical Datum of 1929 (NGVD 29)– Superseded by NAVD 88– Normal Orthometric Heights
• North American Vertical Datum of 1988 (NAVD 88)– Principal vertical datum for CONUS/Alaska– Helmert Orthometric Heights
Geoid• “The equipotential surface of the Earth’s gravity field which best
fits, in the least squares sense, (global) mean sea level.”*
• Geoid surface is neither visible or directly measureable.
• Geoid is mathematically related to and modeled from gravity data.
• A geoid height is the ellipsoidal height from an ellipsoidal datum to a geoid.
• Hence, geoid height models are directly tied to the geoid and ellipsoid that define them (i.e., geoid height models are notinterchangeable).
*Definition from the Geodetic Glossary, September 1986
Daniel R. Roman, National Geodetic Survey, National Oceanic and Atmospheric Administration
ELLIP H (12/06/04) 190.415 (m) ELLIP H (12/18/02) 190.411 (m)
North American Datum Versions • North American Datum of 1927 (NAD 27)
– Superseded by NAD 83
• North American Datum of 1983 (NAD 83)– Original release: NAD83(1986)– 1997 adjustment: NAD83(1997)– 2007 adjustment: NAD83(2007)
NAD 83 Evolution Summary
• 1986 original release– Based on terrestrial data only
• 1997 adjustment– Based on terrestrial and
GPS data combined• 2007 adjustment
– Based on GPS positions only– Fixed to CORS network
Positional Accuracy EvolutionTIME NETWORK LOCAL
NETWORK SPAN ACCURACY ACCURACY
NAD 27 1927-1986 10 METERS (1 part in 100,000)
NAD83(86) 1986-1990 1 METER (1 part in 100,000)
HARN 1990-1997 0.1 METER B-order (1.0 ppm)A-order (0.1 ppm)
CORS 1996 - 0.01 meter 0.01 meter
High Accuracy Reference Network (HARN)A cooperative program started in 1986 by National Geodetic Survey (NGS)
Started in TENNESSEE, and ended in Indiana in 1997
Control “Network”Redundancy!
“TGRN”
Two types:
Lambert Conformal Conic Projection
Transverse Mercator Projection
State Plane Coordinate Systems(SPCS)
Projecting a round surface onto a flat surface.
Transverse Mercator Projection
Lambert Conformal Conic Projection
TennesseeState Plane Coordinate System
Lambert Conformal Conic Projection
34-20 N
36-25 N
False Easting
Lambert Conformal Conic Projection
Intersection of cylinder and ellipsoid
Ellipsoid
ConeIntersection of cone and ellipsoidSCALE EXACT
State Plane Coordinates
Zones: the limits of a projection that do not exceed 158 miles (Lambert), so that the North-South distortions are 1/10,000 or less. Tennessee has only one zone.
Grid Distances are Smaller than Geodetic Distances.