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Lecture BasicGeodesyConcepts

# Lecture BasicGeodesyConcepts - Lecture Basic Geodesy...

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Lecture Basic Geodesy Concepts Lecture Notes Text Coverage: Wolf and Ghilani: Study: Ch 19: 1-18 Problems: 19: 1-13 Geodetic surfaces: Geoid – equipotential gravity surface, undulates, rises under a continent, deflection of the vertical, Everest trying to close a triangle in north India, at all points perpendicular with the direction of gravity, geoid height measured above/below geoid, NGS Geoid 99, Geoid 03, Geoid 06. at higher elevations equipotential surfaces are not parallel with those at sea level, they converge toward the poles. This requires an "orthometric correction" for leveling that has a large N-S component of coverage. NGVD 1929 – a geodetic leveling datum – an early attempt to extend a geoid under the North American Continent that approximates mean sea level on all three coasts. 26 selected tide stations. take tide readings 19 years, average hourly readings for MSL at each station. level between these MSL heights with a transcontinental grid of first order leveling, "tilt" the surface to match these 26 MSL's in a least squares adjustment, Pacific Ocean 30 ft higher than Atlantic. This is our older leveling datum. Quad sheet contours and elevations are referenced to NGVD. NAVD 1988 – a newer geodetic leveling datum that attempts to establish a true geoid under North America.

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Lecture BasicGeodesyConcepts - Lecture Basic Geodesy...

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