Accuracy Assessment an Improvement for Level Survey Survey using Real Time Kinematic (RTK) GPS
Results
The Result obtained room the accuracy analysis in static and kinematic mode are discussed below. Figure 2 shows the minimum observation time to achieve 20 cm precision as a function of base length in static mode with RT20. RT20 is the proprietary algorithm developed by Novatel for phase observation using single frequency GPS in real time.
Figure 2
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Figure 3
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Figure 4
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Figure 5 |
Figure 3 and 4 shows the horizontal and vertical accuracy that can be achieved at a base length of 13 km as a function of observation time period. An accuracy of 20 cm be achieved after 30 minutes observation for the horizontal component. It takes more than 45 minutes for the vertical component to give the same level of accuracy. The height accuracy is less than the horizontal accuracy.
Figure 5 shows the comparison of accuracy that can be achieved with real time (with RT20, carrier phase observation ) and post processing ( with out RT20, only code phase ) . the accuracy achieved in carrier phase with RT 20 is better than the accuracy achieved by code phase.
Figure 6 shows the results of the kinematic survey for height accuracy assessment. The height value observed in RTK mode was compared with the level survey. The RMS error varied from 8 cm to 30 cm for different tests. The error thus achieved in figure 6 was analysed fro further improvement. Figure 7 shows that there is no relation between the antenna velocity (vehicle speed ) and he accuracy. It could be possible to improve the accuracy, as the RMS error is more than the standard deviation of the errors ( comparing figures 7 and 8 ). Figure 9 shows that the errors in figure 6 are linear, they are not changing randomly. Thus a liner equation was applied to improve the accuracy by taking two calibration points at pier no 1 and 31.
Figure 6
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Figure 7
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Figure 8
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Figure 9 |
The equations applied were:
e
0 = h
rtk,0 -h
true,0
e
n = h
rtk,n - h
true,n
h
i = h
obs - e
i
where
h
i is the corrected height at i
th observation
h
obs is the observed height
e
i is the error tern ( error correction to be applied)
e
o 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
d
i is the distance from the calibration point 1, to the point where the error is toe be applied
d
n is the total distance between the two calibration points, Pier 1 and pier 31.
