geoidal การใช้

• The geometrical separation between it and the reference ellipsoid is called the geoidal undulation.
• The geometrical separation between the geoid and the reference ellipsoid is called the geoidal undulation.
• Variations in the height of the geoidal surface are related to density anomalous distributions within the Earth.
• Accretion occurs over geoidal lows that can be caused by avalanche slabs or the downgoing limbs of convection cells.
• Synthetic calculations show that the geoidal signature of a thickened crust ( for example, in orogenic belts produced by continental collision ) is positive, opposite to what should be expected if the thickening affects the entire lithosphere.
• As a vertical deflection describes the difference between the geoidal and ellipsoidal normals, it represents the horizontal gradient of the undulations of the geoid ( i . e ., the separation between geoid and reference ellipsoid ).
• The North American Datum of 1927 ( NAD 27 ) is " the horizontal control datum for the United States that was defined by a location and azimuth on the Clarke spheroid of 1866, with origin at ( the survey station ) Meades Ranch ( Kansas ) . " . . . The geoidal height at Meades Ranch was assumed to be zero, as sufficient gravity data was not available, and this was needed to relate surface measurements to the datum . " Geodetic positions on the North American Datum of 1927 were derived from the ( coordinates of and an azimuth at Meades Ranch ) through a readjustment of the triangulation of the entire network in which Laplace azimuths were introduced, and the Bowie method was used . " ( http : / / www . ngs . noaa . gov / faq . shtml # WhatDatum ) NAD27 is a local referencing system covering North America.