ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
kilometers. A data rate of 1 Hz was used for the kinematic test. 
In addition to the real-time RTK position outputs, the raw 
measurements from both the reference and the rover receivers 
were also saved for post-processing. 
To assess the kinematic positioning accuracy, a high precision 
reference trajectory of the vehicle must be established. In this 
investigation, the raw measurements collected during the 
kinematic test were post-processed using a commercial 
software package and the position results were then used as the 
reference. Compared to the reference position results, the 
accuracy of the real-time RTK position outputs could then be 
assessed. 
Shown in Figure 6 are the PDOP values and the number of 
visible satellites for the kinematic test during which the PDOP 
value was around 2.0 while the number of visible satellites was 
from 7 up to 9. Shown in Figure 7 are the time series of the 
position differences between the reference and the real-time 
position results. The results have indicated that the kinematic 
positioning accuracy was at the order of a few centimeters for all 
coordinate components. 
The mean differential data latency over the Internet for the 
kinematic test is 1.0 second while the minimum and the 
maximum latency values are 0.5 second 3.3 seconds, 
respectively. Large latencies were an indication that the traffic 
between the reference and the rover receivers over Internet was 
heavy. 
GPS Time (s) 
♦ Satellite Number 
» PDOP 
Figure 6: PDOP and Number of Visible Satellites in Kinematic Test 
x Lat. 
+ Lon. 
x Height 
0.20 
0.15 
0.10 
0.05 
0.00 
-0.05 
-0.10 
-0.15 
82400 
82600 
83000 83200 
GPS Time (s) 
83400 
83600 
82800 
Figure 7: Kinematic Internet-based RTK Positioning Accuracy 
6. CONCLUSION 
The concept of conducting differential satellite positioning over 
Internet has been described in this paper. In addition to the 
Internet advantages for wireless communication, the use of 
Internet to develop innovative applications using satellite 
navigation systems has also be explored including the 
introduction of a new mobile-to-mobile solution for multiple 
moving platform application. 
To validate the concept, a prototype system has been 
developed and tested in the field. The test results have 
demonstrated that the data transmission latency over the 
Internet is typically at the level of one second while the 
obtainable positioning accuracy is at the centimeter level when 
using Real-Time-Kinematic (RTK) technology. As the fast 
advances of the Internet technology and its increased 
accessibility in the near future, Internet will help the 
development of new location system and device, not only cost- 
effective but also available anywhere at anytime, to support a 
wide range of applications including the emerging location- 
based services (LBS). 
ACKNOWLEDGEMENT 
This research is partially supported by the Geomatics for 
Informed Decision (GEOIDE) Program of Network Centre of 
Excellence (NCE) and the Co-ordination of University Research 
for Synergy and Effectiveness (COURSE).