P2-9-4 
Measurement Point 
Revolving Laser Level 
Figure 4 Measurement using Laser Level 
Figure 5 Concept Drawing of Measurement System Using GPS and Laser Level 
play 2 roles in this system as shown in Figure 6. 
The basic idea of this principle is to take advantage of the 
fact that the laser level can provide extremely high accuracy 
of several millimeters. Using this feature, 
the height of the laser level (RH) can be measured at the 
same time from the height of GPS fixed on top of the laser 
receiver (GH) and the laser level measurement (Rh). 
RH = GH - (GK - Rh) • • • Equation 1 
Since this.value contains a GPS fluctuation error, it must be 
adjusted during the observation time. The adjusted value 
MRH is derived from Equation 2. 
MRH = 2 RHi / n ... Equation 2 
(Value "n" must be greater than 14400 because 4 hours or 
longer adjustment processing is required and the data update 
rate is 1 second.) 
Therefore, if the GPS and laser receiver heights are recorded 
continuously while moving the laser receiver and observing 
several survey points, the laser level altitude can be deter 
mined accurately by post-processing with Equations 1 and 2. 
Figure 7 shows the equipment mounted on a normal auto 
mobile, and Figure 8 shows a scene of the survey using the 
vehicle. 
4. Accuracy, Efficiency, Usability 
1) Accuracy 
Based on the performance of each piece of equipment of 
this system, we estimate that the accuracy of the entire sys 
tem will be within ± 2 cm for a survey range of about 3 ~ 4 
km. 
An example of the results for a test survey conducted at 
Tokyo International (Haneda) Airport is shown in Figure 
12. In a comparison with the results of a cautious survey 
conducted using the auto level, all measurements were within 
± 2 cm. 
2) Efficiency 
Because this system is mounted on a survey vehicle and 
provides continuous measurement while driving, work effi 
ciency was significantly improved over the conventional 
method of stopping at each survey point.. 
Based on the work efficiency data of the test survey, we 
estimate that the work efficiency tripled the conventional rate 
in terms of efficiency per day (km/day), and was 5 times or 
greater in terms of efficiency per day per person (km/person,