ul 2004 
\-5V 
filter) 
IC 
  
DC 
  
3-35FD 
  
  
3.2 Fixed and moving coordinate systems 
Two kinds of coordinate system are used in the 
experiments: the one denoted by X(XYZ) is fixed to the 
ground such that X-Y plane is horizontal and X-axis 
directs toward magnetic north, and the other one denoted 
by X(xyz) moves with the equipment. They shall be 
called the fixed coordinate system and the moving 
coordinate system, respectively. Both systems coincide 
with each other at the beginning of the experiment, but 
the system Z(xyz) translates and rotates as the inertial 
navigation system goes along the route. Accelerations 
and angular velocities obtained from the sensors are the 
vector components in the moving coordinate system 
X(xyz). Therefore, they are transformed into those in the 
fixed coordinate system Z(XYZ) before integration, and 
the rest of the computations (e.g. positioning and error 
evaluation) are performed in Z(XYZ). 
Fiber optical gyro (a) 
  
120 
100 
X[North-South][m] 
3 
  
  
-250  -200  -150  -100 -50 0 50 
Y[East-West][m] 
0.9[m/s] (.4{mys] - - - -2.7[nvs] | | 
  
  
  
True value 
  
Vibration gyro 7 (b) 
350 ets eee e ree eta te ie RS, 
  
100 
Un 
© 
X[North-South][m] 
© 
  
-50 
-100 
-600 -400 -200 0 200 
Y[East-West][m] ; 
0.9[m/s] 1.4[m/s] - - - -2.7[m/s] 
  
  
  
  
== True value 
Figure 5. Estimated trajectories projected onto 
a horizontal plane (nonstop strategy) 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part BS. Istanbul 2004 
    
  
   
   
   
   
    
    
    
   
    
   
  
  
    
       
    
     
     
       
     
    
   
  
   
  
  
    
3.3 Effects of the moving speed 
In inertial survey, the distance is obtained by integrating 
the acceleration twice, and the angular change is 
obtained by integrating the angular velocity once. The 
error accumulates and increases with the lapse of time, 
and hence it seems desirable to finish the measurement in 
shorter time to make the positioning more accurate. In 
order to ascertain whether this inference is correct or not, 
experiments were repeated changing the moving speed of 
the equipment. The nonstop strategy is adopted in this 
experiment with three kinds of moving speed: slow 
(approximately 3 min. to go around whole the route, 
approximately 0.9 m/s), medium (2 min., 1.4 m/s) and 
fast (1 min., 2.7 m/s). 
  
  
  
  
  
  
  
  
| Fiber "optical gyro (a) 
| 
pU. 777 ee 
x 1 
| ce 
| & 150 
15 e 
| ago ——— 314 
1.8 50 
+ 0 
0 | 2 S 
| 
} 
Moving speed[m/s] 
| 
  
/* O.9[n/s]  14[n/s] 4 2.7[m/s] — Approximate curve 
  
  
Vibration gyro (5) 
1000 
800 
600 
400 
200 
Horizontal Discrepancy[m] 
  
0 | 2 
o 
Moving speed[m/s] 
  
  
, € 0.9[m/s] M1.4[m/s] 4 2.7[m/s] — Approximate curve 
  
  
Figure 6. Dependence of the horizontal discrepancy 
on the moving speed (nonstop strategy) 
Figure 5(a) shows the estimated trajectories by the 
inertial navigation system equipped with fiber optical 
gyros. They are projected onto a horizontal plane. Thick 
solid curve represents the true trajectory mentioned in 
section 3.1, and other three curves stand for the estimated 
trajectories in cases that the moving speed is slow, 
medium and fast, respectively. As has been expected, the 
discrepancy between the true and the estimated 
trajectories decreases as the moving speed increases. If