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Figure 1 Concept Drawing of RTK-GPS 
NASU 
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Figure 2 RTK-GPS Height Measurement 
3.2 Outline of Laser Level 
As shown in Figure 4, laser level measurement 
uses a revolving laser level that rotates the horizontally 
emitted laser beam to form a horizontal control plane, and 
at the laser beam receiver that receives the laser beam. 
The laser level emitter has a horizontal plane setup accu 
racy of within ±5 mm at 100 meters away, and can mea 
sure up to about 200 meter radius. 
The laser level receiver automatically reads the height 
position of the received laser beam and outputs the data to 
a computer, thus free of read errors allowing higher pro 
cessing efficiency. 
3.3 Principle of the Developed System 
We will explain the mechanism of this system using the 
concept drawing shown in Figure 5. A laser level is set 
up over a control point which will produce a horizontal 
plane of rotating laser beam. The height relative to that 
plane is measured using a laser receiver. 
However, the measurement position of the survey point 
cannot be measured with the laser level. Here, we can use 
Figure 3 Relationship between Adjustment 
Fluctuation 
GPS to determine the position, thus able to determine the 
relative height of the position and the laser level. This is 
the basic principle of this system. 
To derive the altitude from the relative height, it is neces 
sary to measure the reference height of the laser level. 
One way to do this is to use the conventional leveling sur 
vey technique. However, in cases where the entire ground 
level subsides as in the case of airport islands, the mea 
surement must be determined from a stable leveling point far 
away, which will be inefficient. 
On the other hand, by placing a GPS antenna on top of the 
laser level and conducting continuous observation over a long 
period of time, we can determine the accurate altitude by ad 
justing the acquired data. 
By establishing a GPS control station over a leveling point 
near the airport, this method will be an extremely convenient 
solution. However, this requires 2 units of expensive GPS, 
becoming a cost problem. 
Another way is to use 1 unit of GPS and place it on the laser 
receiver and the laser level in turns, but since it takes nearly 4 
hours to accurately determine the altitude of the control sta 
tion, this will be a very inefficient solution. 
We came up with an alternative of using 1 unit of GPS to 
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