37 
PROCESSING CENTER 
ROVER STATION 
MODEM ' - 
PaJkFinder 
flOTsi 
V A 
CPS SIGNAL 
V 
CSM 
MOPtM 
f Prq.XRS 1 
Asgen ~ 
D 
MASTER STATION 
Figure 13 A configuration of a GPS based Positioning system 
for road survey 
5. CONCLUSION 
In the framework of road survey the use of GPS is necessary 
when the positioning has referred to an absolute reference 
system, which allow data representation in a mapping 
projection. In order to guarantee the continuity of the 
positioning, the presence of other sensors (odometer or 
platform) is still convenient (Schwarz, 1993, Wong, 1988). 
Furthermore, to maintain the compatibility with data collected 
during standard road survey, the extraction of a mile chainage 
should be considered. In general, the GPS derived mile 
chainage can be easily overestimated unless a more advanced 
procedure is implemented. With the approach adopted in this 
work, the mean difference observed between GPS and 
odometer chainage was within 3 meters. 
The performance of the RTCM satellite transmitted correction 
for differential positioning was positively evaluated along 50 
km of highway. The positional accuracy level of the RTMC 
mode resulted comparable to the one relative to the post- 
processed mode. In consideration of the major operational 
advantages, the RTCM technique can be efficiently adopted for 
road surveys requiring meter-level positional accuracy. 
6. REFERENCES 
Radio Technical Commission for Maritime Services Special 
Committee 104, Recommended Standards for Differential GPS 
Services, ver. 2.0, Washington DC, January 90. 
Greenspan R. L. (1996). GPS/Inertial Integration Overview, 
Global Positioning System: Theory and Applications, vol. 2 
(Ed. B. W. Parkinson and J. J. Spilker), vol. 163 of Progress in 
Astronautics and Aeronautics, AIAA, pp. 187-218. 
Seeber G., Boder W., Goldan H., Schmitz M., Wübbena G. 
(1995) Precise DGPS Positioning in Marine and Airborne 
Applications. In GPS Trends in Precise Terrestrial, Airborne 
and Spaceborne Applications, I AG Symposia 115, Springer, 
202-21 
Schwarz K. P. (1993). Integration of GPS and INS, 
Proceedings of Workshop on Airborne Geophysics, 
Washington D.C., July 12-15, 1993, pp. 34-54. 
Schwarz K. P„ M. E. Cannon and R.V.C. Wong (1989). A 
comparison of kinematic models for the determination of 
position and velocity along a trajectory, Manuscripta 
Geodaetica 14, pp. 345-353. 
Trimble SURVEY CONTROLLER, Reference Manual, USA, 
September 1997 
Trimble ASPEN GPS System Operation Manual, USA, June, 
1997 
Wong R.V.C., K. P. Schwarz, and M. E. Cannon (1988). High- 
Accurate Kinematic Positioning by GPS-INS, Navigation, Vol. 
35, No.2, Summer 1988. 
AKNOWLEDGEMENTS 
This work has been carried out in support of the technical staff 
of the “Funzione Centro Ricerche e Sviluppo per i Lavori 
Autostradali/Automezzi e Macchine Speciali” of the “Società’ 
Autostrade”. In particular the authors acknowledge Ing.Fornaci 
and Ing. Drusin for the assistance and contribution during the 
operational and processing phases