When optical leveling is done, the path corresponds closely to following a value of dynamic height horizontally, but to orthometric height for vertical changes measured on the leveling rod.
12.
In Albania ( normal-orthometric height ) they also refer to heights as'metres above the Adriatic', but use a specific tide gauge in the port of Durr�s.
13.
The NHN was introduced because for heights above the actual normal orthometric heights ( new methods of calculation ) and the normal heights of East Germany ( with respect to the Amsterdam Datum ).
14.
GPS measurements give earth-centered coordinates, usually displayed as height above the reference ellipsoid, which cannot be related accurately to orthometric height above the geoid without accurate gravity data for that location.
15.
As gravitational potential cannot be neglected for applications with high accuracy requirements, the Swiss national height network 1995 ( LHN95 ) created a new orthometric height vertical reference point, fixed to the geoid.
16.
Orthometric height is for practical purposes " height above sea level " but the current NAVD88 datum is tied to a defined elevation at one point rather than to any location's exact mean sea level.
17.
For example, gravity is 0.1 % stronger in the northern United States than in the southern, so a level surface that has an orthometric height of 1000 meters in Montana will be 1001 meters high in Texas.
18.
Normal gravity values are easy to compute and " hypothesis-free ", i . e ., one does not have to know, as one would for computing orthometric heights, the density of the Earth's crust around the plumbline.
19.
Practical applications must use a model rather than measurements to calculate the change in gravitational potential versus depth in the earth, since the geoid is below most of the land surface ( e . g ., the Helmert Orthometric heights of NAVD88 ).
20.
"' VERTCON "'is a computer program that computes the modeled difference in orthometric height between the North American Vertical Datum of 1988 ( NAVD 88 ) and the National Geodetic Vertical Datum of 1929 ( NGVD 29 ) for a location in the contiguous United States.
