3-3-5 
The equations applied were: 
e 0 = hrtk, 0 — h t rue, 0 
Equation 1 
p — h — h 
c 'n n 'rtk,n "'true,n 
Equation 2 
h , = h cbs~ e , 
Equation 3 
where, 
hi is the corrected height at i th observation 
h 0 bs is the observed height 
ei is the error term (error correction to be 
applied) 
ei is given by: 
correction 
C: — e n + 
e„ —e, 
d. 
*d ; 
Equation 4 
Where, 
• e 0 is the error between the RTK Height 
and the True value at Calibration Point 
1 
• e n is the error between the RTK Height 
and the True Value at Calibration Point 
2 
RTK Height 
Standard 
Deviation 
RMS Error 
Before 
Correction 
7cm ~ 12cm 
8cm ~30cm 
After 
Correction 
1cm ~ 3cm 
2cm ~ 4cm 
Table 1: Comparison of Accuracy 
• di is the distance from the calibration 
point 1, to the point where the error is 
to be applied 
• d n is the total distance between the two 
calibration points, Pier 1 and Pier 31 
Figure 10 shows the results before and 
after applying the error correction 
equations. The accuracy thus improved is 
listed in Table 1. 
5. CONCLUSIONS 
• Based on the above results and 
analysis, it can be concluded that the 
height accuracy can be improved to 2- 
4cm (RMS) for a base length of three 
kilometers. This is achieved by 
applying the error correction to the data 
observed in RTK mode. 
• A GPS base station has been 
established at Asian Institute of 
Technology (AIT), Thailand, using 
mobile phone for real time differential 
correction. 
• It was found that there was no effect of 
antenna velocity on accuracy. Thus the