Geoscience Reference
In-Depth Information
Fig. 5.33 Correction from
normal section to geodesic
measured by GPS to the angles with respect to the plumb line and convert the
direction of the center of the station mark to the direction of the target point.
In real operations, it is regulated that the reduction is accurate to 0.001
00
in the
first-order triangulation, 0.01
00
in the second-order triangulation, and 0.1
00
in the
third- and fourth-order triangulations. Hence, not all three corrections for horizontal
directions need to be computed for triangulation in all order types. They are based
on the magnitude of the numerical values of each correction and the requirements
for the decimal place. This is summarized in Table
5.5
.
Sample computations of the three corrections for horizontal directions are as
follows:
1. Computational Formulae
9
=
;
tan
ʴ
1
00
00
sin A
1
ʷ
00
cos A
1
ﾼʾ
ʱ
00
e
2
H
2
ˁ
ʴ
2
00
cos
2
B
2
sin 2A
1
ﾼ
2M
2
e
2
S
2
00
ˁ
ʴ
3
00
cos
2
B
1
sin 2A
1
ﾼ
12N
1
p
1
ð
5
:
58
Þ
e
0
2
cos
2
B
V
ﾼ
þ
c
V
N
ﾼ
N
V
2
ʣʴ ﾼ ʴ
1
þ ʴ
2
þ ʴ
3
M
ﾼ
2. Example
In Fig.
5.34
is a schematic view of the triangulation network formed by Wang
Village, Zhang Village, Long Mountain, and Gao Mountain. The known data;
and the values of observed directions in the computations of three corrections for
horizontal directions are given in Tables
5.6
and
5.7
) (Krassowski Ellipsoid,
Beijing Coordinate System 1954 adopted)
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