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Due to the rapid development of GPS technique in recent years,
we can obtainhigh-precision ellipsoidal heights with a
relative accuracy on the order of0.1 to 1 ppm. GPS technique
changes the face and concept of traditional heigh-ting
procedure. However, because leveling height is orthometric and
GPS heightis ellipsoidal, geoidal undulation is essential for
relating the two. Geoidalundulation can be obtained by
measuring local gravity anomalies and globalgeopotential model.
The purpose of this research is to integrate leveling,GPS and
gravity obser-vations to construct a height adjustment model
, to predict the accuracy oforthometric height and geoidal
height for the first-order benchmarks and theaccuracy of
geoidal height for the first-order satellite control points
inTaiwan.
Taiwan''s traditional horizontal and vertical control systems are
independentwith each other. The adjustment of the first-order
satellite control networkhas just completed in 1997. Therefore
, there is high-precision ellipsoidalheight for each first-
order satellite control point. Therefore, by predictingthe
accuracy of the geoidal height of the first-order satellite
control pointsone can build a three-dimensional control system
for Taiwan. Considering using only one mean
sea level reference point in Keelung definedas the origin of the
height datum,with 2km average distance between
contiguousbenchmarks on leveling line, 10km average distance
between contiguous GPS sta-tions on leveling line , 2''×2'' grid
gravity anomalies and five high-precisionGPS baselines (Keelung-
Taichung, Taichung-Kenting , Kenting-Hualien , Hualien-Keenlung,
Keenlung-Kenting) , the best heighting accuracy is achieved. The
or-thometric height standard deviation increases from the
origin of the datumtoward south , and arrives at ±3.5cm
maximum in Kenting. The geoidal heightstandard deviation shows
the same tendency , but smaller in Taichung, Kenting,and Hualien
because of the introduction of the five high-precision GPS
base-linesas constraint. The maximum formal error of benchmarks
is ±4.4cm, and themaximum formal error of geoidal height on
first-order satellite control pointsis ±4.7cm.
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