Positive height system

Elevation system

Often engaged in foreign surveying and mapping projects , They usually use Zhenggao system , I feel there is no difference in the principle , A geoid , The other is quasi geoid
It's high （H）： This is the elevation of a point above the geoid . It is measured along a plumb line perpendicular to the equipotential plane . （ Company ： rice ）
Height （N）： This is the reference ellipsoid （ for example GRS80） Measure distance with geoid along ellipsoidal normal . Geoid height is also called geoid undulation .（ Company ： rice ）
Geodetic height or ellipsoidal height （h）： The elevation of the point above the reference ellipsoid . Measure the distance along the normal of the ellipsoid . （ Company ： rice ）