Geoscience Reference
In-Depth Information
geometric derivation based on the four defining parameters
a, f, GM, ω
yields
C
20
=
−
0
.
484 166 774 985
·
10
−
3
which differs from the original value by
10
−
11
. For many more details refer to National Imagery and Map-
ping Agency (2000).
We conclude these considerations by a useful table. Using the four defin-
ing parameters, it is possible to derive the more commonly used geometric
constants and physical constants (Table 2.4) associated with the WGS 84
reference ellipsoid.
7
.
5015
·
Numerical comparison of GRS 1980 and WGS 84
As mentioned previously, the GRS 1980 is the basis of the WGS 84. However,
due to different defining parameters on the one hand and, e.g., a refined value
for
GM
for the WGS 84 on the other hand, numerical differences between
the GRS 1980 and the WGS 84 arise. Some of these differences are given in
Table 2.5.
Table 2.5. Numerical comparison between GRS 1980 and WGS 84
Parameter
GRS 1980
WGS 84
10
8
m
3
s
−
2
10
8
m
3
s
−
2
GM
3 986 005
·
3 986 004
.
418
·
1
/f
298
.
257 222 101
298
.
257 223 563
b
6 356 752
.
3141 m
6 356 752
.
3142 m
e
2
0
.
006 694 380 022 90
0
.
006 694 379 990 14
e
2
0
.
006 739 496 775 48
0
.
006 739 496 742 28
E
521 854
.
0097 m
521 854
.
0084 m
c
6 399 593
.
6259 m
6 399 593
.
6258 m
62 636 860
.
850 m
2
s
−
2
62 636 851
.
7146 m
2
s
−
2
U
0
9
.
780 326 7715 m s
−
2
9
.
780 325 3359 m s
−
2
γ
a
9
.
832 186 3685 m s
−
2
9
.
832 184 9378 m s
−
2
γ
b
m
0
.
003 449 786 003 08
0
.
003 449 786 506 84
2.12
Anomalous gravity field, geoidal undulations,
and deflections of the vertical
The small difference between the actual gravity potential
W
and the normal
gravity potential
U
is denoted by
T
,sothat
W
(
x, y, z
)=
U
(
x, y, z
)+
T
(
x, y, z
) ;
(2-224)
