1.8 Survey of SLR Telescope Reference Point
(1) Survey method
1) In 1999, the method of positioning
the reference point of SLR telescope has been changed to gindirect methodh,
since the setting of survey target at the reference point has been found to be inadequate
when the survey has been conducted by gdirect methodh in 1997 and 1998.
2) The indirect method applied here
was a method to measure the survey targets placed near the reference point of
SLR telescope from the three long pillars by using TS. AT each long pillar, the azimuth angle
of SLR telescope has been adjusted to face the long pillar, and observations
are made while SLR telescope is rotated to three positions along its elevation
axis with an interval of approximately 45 deg. In this way, nine positions of
the target on a sphere are gained. The method of least squares was applied to
calculate the positioning coordinate of the spherical center (reference point)
from these nine positionfs coordinates.
3) However, at Koganei station, instead of using
the long pillars (L1, L2, L3), base points (X1, X9, X10) have been used as the
instrument points of TS. And at Tateyama station, base point (X1) has been used
as the instrument point of TS instead of the long pillar (L3).
(2) Survey results
1) As
displayed in Table 15, the result gained from the calculation of the spherical
center (reference point) by applying the method of least squares to the nine
coordinate values observed in 1999 survey by the gindirect methodh showed
evidently that the reference point was appropriate at all observation stations.
Table 15 Results of the calculation of the spherical center using the method of
least squares
Observation station 
Maximum value of the residual (mm) 
Standard deviation of the spherical center
(mm) 

X 
Y 
H 
SD_{X} 
SD_{Y} 
SD_{H} 

Koganei 
0.2 
0.2 
0.2 
0.2 
0.3 
0.2 
Kashima 
0.2 
0.1 
0.1 
0.1 
0.1 
0.1 
Miura 
0.1 
0.1 
0.1 
0.1 
0.1 
0.1 
Tateyama 
0.2 
0.2 
0.2 
0.2 
0.1 
0.1 
* X,Y respectively represent the southnorth and eastwest
component of the plane Cartesian coordinate system. H represents the vertical
component.
2) Table 16 shows the comparison of the
coordinates of SLR telescope reference point by gindirect methodh in 1999 and
those by gdirect methodh in 1997 and 1998 respectively.
Table
16 Difference of coordinates of SLR
telescope reference point obtained in 1997 and 1998 compared to that in 1999.
(unit: mm)
Year 
Koganei station 
Kashima station 
Miura station 
Tateyama station 

N 
E 
U 
N 
E 
U 
N 
E 
U 
N 
E 
U 

1997 
0.4 
0.4 
1.7 
0.2 
0.6 
2.1 
0.7 
0.2 
5.0 
0.2 
2.5 
2.0 
1998 
1.6 
1.5 
1.9 
0.6 
0.6 
1.5 
0.2 
0.0 
1.9 
0.4 
1.7 
1.4 