refer to
http://webhelp.esri.com/arcpad/8.0/referenceguide/index.htm#gps_rangefinder/concept_gpsheight.htm
1.HAE: Height above ellipsoid
是天线到地球表面(球形模型)的距离.
2.MSL: Mean Sea Level
HAE = MSL_Height + GeoidSeparation
HAE是比MSL准确,是因为通过球形模式坐标来计算,而海平面是不规则的,很难计算,所以不准确.