NT P1268 Dunmarra Elevation Grid Geodetic

Digital Elevation Model data record the terrain height variations from the processed point-located data recorded on an airborne geophysical survey.� The aircraft altimeter data records the height of the aircraft above the ground and the aircraft GPS records the height of the aircraft above the ellipsoid.� Subtracting the two values enables the height of the terrain beneath the aircraft relative to the ellipsoid to be calculated.� This ellipsoidal terrain height is corrected for the variation between the ellipsoid and the geoid (the n-value correction) to produce terrain heights relative to sea level.

数字高程模型（Digital Elevation Model, DEM）数据依托航空地球物理勘测中采集并经处理的点位数据生成，用于记录地形高程的起伏变化。飞机高度计数据可记录飞行器距地面的高度，机载GPS（Global Positioning System）则记录飞行器相对于参考椭球体的高度。将两组数值相减，即可计算出飞行器下方地形相对于椭球体的高程。随后针对椭球体与大地水准面之间的偏差（即n值校正）对该椭球地形高程进行修正，最终得到相对于海平面的地形高程。