ınbul 2004 
ASSESSMENT OF VRS-GPS FOR PRACTICAL APPLICATION 
TO LOCAL CONTROL SURVEYING 
X. WU, K. Mishima”, T. Sasagawa“, Y.Mishima®, K. Tatibana“, K. Honji* *, 
* PASCO Corporation, 153-0043 Tokyo, Japan - (shinka go, kenji mishima, tadashi sasagawa 
, 
yoshinori mishima, kikuo tachibana, koichi honji)(g)pasco.co.jp 
PS ThS16 
KEY WORDS: RTK-GPS, VRS, GEONET, Geodetic Coordinates 2000, Public Survey, Local Control Point 
ABSTRACT: 
With the geodetic datum switching over to JGD2000 (Japan Geodetic Datum 2000) and the opening of GPS data in real time 
observed by GEONET (GPS Earth Observation NETwork) system, it has been expecting to use the data in surveying of local control 
points, public survey and so on. It is considered that a new method of RTK-GPS positioning called VRS (Virtual Reference Station) 
is a prevailing technique for higher precise positioning in real time with higher efficiencies and lower costs by using the minor 
multiple reference stations of GEONET in a wider area. In order to verify practical applying and the positioning precision of the new 
RTK-GPS by VRS at the local control points for public survey, field experiments are carried out. As the result of observation, the 
standard deviation in 3-components of positioning by VRS-GPS is about 2 cm in horizontal and less than 4 cm in vertical. Since the 
environment for GPS observation in real time is not very good in the residential area of city, there is potentiality for higher 
positioning precision for VRS-GPS positioning in comparatively better environment. This paper gives a detailed report about the 
experimental results, the ways for solving some problems and conclusions. 
1. INTRODUCTION 
li is well known that there are some limitations in GPS 
positioning survey by the traditional way of RTK, both in the 
cost and the precision. For example, an additional set of GPS 
receiver is needed for rover's own reference station, but also it 
Is necessary to spend time and energy for setting it. Moreover, 
the precisions of survey results are under many restrictions such 
as the distance of baseline between the reference station and the 
rover, simply the longer a baseline is, the more likely the 
positioning precision is to fall down due to the effects of the 
ionosphere and the troposphere. 
However, a new method of RTK-GPS positioning called VRS 
(Virtual Reference Station), as a prevailing technique for higher 
precise positioning in real time with higher efficiencies and 
lower costs, can resolve such problems as mentioned above. 
Because of a wide network covered by multi-reference stations 
is used to create a VRS near rover, it is possible to do precise 
positioning surveying everywhere in a wide area just by 
receiving the correction data from a LBS (Location Business 
Service), not need to set rover's own reference station one by 
one in a wide area. 
As one of the largest and densest permanent GPS arrays in the 
world with more than 1200 GPS stations (up to 2003) at an 
average separation between the stations each other of about 25 
km, the GEONET (GPS Earth Observation NETwork) just 
provides an ideal infrastructure for the new RTK-GPS by VRS. 
GEONET has been constructed by GSI (Geographical Survey 
Institute) for monitoring crustal deformation in Japan since 
1993. Now, it covered the Japanese islands as not only a 
foundational monitoring network of crustal deformation, but 
also the new geodetic control points of Japan. 
  
Corresponding author: Koichi Honji 
865 
Since continuous observation is been operating by every station 
24 hour per day, in a sense the GPS observation data of 
GEONET is a huge resource. It has been expecting to take the 
multiple reference stations of GEONET as the reference 
network in a wider area and use their data in real time to survey 
local control points for public survey and so on. GPS data 
observed by 200 stations of GEONET was provided in real time 
to the private sector from May 2002. There have been nearly 
1000 stations opened with their real time data since October 
2003. 
In order to verify the validity, practical application of VRS-GPS 
and its positioning precision in local control surveying, some 
field experiments were carried out. This paper reports the 
experimental results and the solutions for solving some 
problems of the actual field observation. Finally, the 
conclusions are given. 
2. EXPERIMENTAL SURVEYING 
The experimental field is located in Toyonaka city of Osaka. 
The surveying by GPS positioning in real time is carried out at 
the 3 and 4" grade local control points total in 32 points that 
are distributed in a residential area and along three routes 
(Figure 1). The experimental contents of RTK-GPS positioning 
by VRS and used hardware & software are shown in Table 1. 
The methods of experiment and their configurations are 
presented in Table 2. 
At each point, the RTK-GPS positioning by VRS is repeated 
under different surveying conditions from January 27 to 31, 
2003. Table 3 gives the details of different surveying conditions 
and ways for RTK-GPS positioning. Figure 2 shows two 
reference networks that VRS is based.