Sect_11.3.8

11.3.8 GPS Heighting

GEOID HEIGHT APPLICATIONS

The various uses of geoid height information, the appropriate geoid height determination technique(s) and the accuracy required are summarised in the Table below.

GPS applications of geoid height data.
N
used for "Order" for N:
specification Possible means of
evaluaitng N

1.) Geophysical exploration; reconnaissance surveys Low:
_N 5.10m Low order ( n_max = 36 ) geopotential models

2.) Transforming between geodetic datums 3rd order:
_N 1.2m High order ( n_max = 180 to 360 ) geopotential models

3.) Control surveys for large mapping; engineering projects 2nd order:
_N 10.20cm over 20 km
(5-10 ppm)

Surface fitting N, as measured by GPS and levelling, or
Detailed gravimetric evaluation

4.) Height control (between 2nd to 3rd order) from GPS; special projects 1st order:
_N 20.30cm over 110 km
(2-3 ppm) Detailed gravimetric evaluations using surface gravity data

GPS applications of geoid height data.
N used for	"Order" for N: specification	Possible means of evaluaitng N
1.) Geophysical exploration; reconnaissance surveys	Low: _N 5.10m	Low order ( n_max = 36 ) geopotential models
2.) Transforming between geodetic datums	3rd order: _N 1.2m	High order ( n_max = 180 to 360 ) geopotential models
3.) Control surveys for large mapping; engineering projects	2nd order: _N 10.20cm over 20 km (5-10 ppm)	Surface fitting N, as measured by GPS and levelling, or Detailed gravimetric evaluation
4.) Height control (between 2nd to 3rd order) from GPS; special projects	1st order: _N 20.30cm over 110 km (2-3 ppm)	Detailed gravimetric evaluations using surface gravity data

Although four categories of user have been identified in the above table, there are in fact two distinct user applications:

the use of geoid heights in the network transformation process, and
converting GPS heights to levelled heights.

These are discussed the next sections.

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