34 
Figure 3 TEST 2: Vehicle Trajectory obtained from the DGPS 
in post-processed survey 
The MASTER station for differentially processing data 
collected by the ROVER receiver (Pro XR) was situated at a 
distance of about 2 kilometres from the test-area. The raw data 
were processed using the PathFinder Office package. The 
displacement that was observed between two repeated tracks 
resulted to be within 2 meters; this value can be addressed both 
to positional errors and to normal route deviations. As 
expected, while passing by the urban area many interruptions 
are present in ROVER data resulting a segmented trajectory 
(Figure 3). 
3.3 TEST 3: Performance of RTCM satellite transmitted 
correction 
The test was carried along several kilometre of the highway 
RM-AQ (Figure 4). This time the vehicle was equipped with a 
Pro XRS receiver, capable of receiving in real time the RTCM- 
104 satellite transmitted correction (via OMNISTAR). While 
running on the highway, the vehicle proceeded twice over the 
same route in both directions: the first time running at a speed 
of 60-80 km/h on the right lane and the second time at 120 
km/h on the take-over lane. 
All the resulting trajectories showed a good level of overlap, 
with the exception of a major divergence visible in the 
northeast end of the trajectory (Figure 4). This effect was 
caused by a defective transmission cable and resulted in a 
displacement that reached the magnitude of 30-40 meters in 70 
epochs. In figure 5, a detail of the trajectories is shown. 
Figure 4 TEST 3: Vehicle Trajectory obtained from the Post 
processing Differential GPS highway survey 
Figure 5 TEST 3: Particular of the Vehicle Trajectory obtained 
from the Post-processing Differential GPS highway survey 
4 SURVEY WITH A DEDICATED VEHICLE 
This test was carried out with a vehicle adopted for highway 
survey by the Società Autostrade. A path of 20 kilometres along 
the Al highway was covered many times back and forth. The 
speed of the vehicle was about 60 -s- 70 kilometres per hour as 
in a standard operational environment. 
The test area was chosen on the basis of different 
characteristics: 
the proximity with the operating base of the Società 
Autostrade in Fiano Romano, where the MASTER station 
was located; 
the continuos presence of a suitable emergency lane. 
In order to establish a number of reference points, 21 marks 
were painted on the ground along the emergency lane in 
correspondence of kilometre road signs (Figure 6). 
Inside the vehicle two receivers were collecting data during the 
test: the Pro XR/XRS and the 4700 Trimble receivers. The first 
one was used either in RTCM-104 mode or in Post Processing 
mode. The 4700, a double frequency receiver with a sub 
centimetre accuracy, was used to compute reference values to 
estimate the accuracy of the Pro XR/XRS positioning. 
Furthermore the positional data measured by the odometer in 
the form of mile chainage, were compared with that one derived 
from the GPS co-ordinates. 
On the roof of the vehicle, equipped with a high quality 
odometer, two GPS antennas were mounted (Figure 7).