ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
The basic idea of WADGPS technology is to distinguish the 
error resources of GPS observation values and model each 
error resource respectively. Then transfer the modified error 
value of each error resource (differential modified value) to 
users through data communication chains. The error of 
observation value of users' GPS receiver will be modified 
accordingly so as to mitigate the effect of those error resources 
and improve user GPS positioning precision. The precision 
may reach 1-5m. The WADGPS model is as follows (Fig.1). 
Fig. 1 WADGPS Model 
No matter it is LADGPS or WADGPS, the users' positioning 
precision is improved by modifying the false-distance error 
according to false-distance scale in a general circumstance. 
However, the highest surveying precision can only reach 1 -5m 
with this method, which is far from the requirement of duct 
system surveying. Hence, in order to increase the positioning 
precision of LADGPS and WADGPS further more, the joint 
research body has studied and proposed that besides 
modifying false-distance error, the carrier phase differential 
modified information should be added to improve users' GPS 
positioning precision. At the same time, it is required that the 
users' GPS should have the function of receiving carrier phase 
modified information. After experimenting, the highest 
precision may reach 1 -2cm with the fastest positioning time per 
single point as 5s. This precision is able to be used to obtain 
the 3-D coordinate of underground pipelines and valves. Even 
it is in hard areas, combining with the routine technologies, the 
objective can still be achieved. Thus, the time to obtain the 
actualization materials of valves and underground pipelines 
can be shortened greatly. 
GPS is able to provide 3-D coordinate, the spatial location, of 
the valves accurately. However, it is unable to distinguish the 
type and attribute of the underground duct system. Especially 
after “Clearance Project" is implemented, the duct system on 
the ground is disappearing. On the contrary, the underground 
pipelines are serried, distributed like spider web. There are 
many kinds of pipelines as sewage drain, flow pipe, gas pipe 
and connections. If the fundamental materials are not accurate, 
the routine repairing and surveying technology can hardly 
obtain the 3-D coordinate of the underground duct system. 
Nevertheless, RS technology may achieve the goal. For 
example, the geophysical detection methods will use the 
reflecting and sending characteristics of the features to 
accurately explore fundamental information of underground 
pipeline network as building materials, diameter and depth of 
burial. Thus, the type of the underground pipelines can be 
judged. Supplemented with GPS simultaneously, the 
actualization materials of the flow pipes will be obtained fairly 
accurately. 
3. APPLYING GIS, REALIZE SCIENTIFIC MANAGEMENT 
AND DECISION-MAKING 
Nowadays, the actualization of the fundamental materials in 
most Urban Water Supply Departments in China is bad. At first, 
the management of fundamental materials is lagged. The 
quantity of fundamental materials with paper or other media as 
the carrier is quite large. They are easy to lose and make the 
materials mutilated. Secondly, the base maps were made a 
long time ago so that the maps are distorted greatly. In addition 
with the cartographic error, the map precision is decreased as 
well as the map using value. Thirdly, the speed of urban 
infrastructure is rapid, the routine surveying technologies can 
hardly meet the urgent demand for infrastructure and 
management. Fourthly, because the actualization of the 
materials is bad, problems as leakage and bursting of pipelines 
cannot be solved in time, which has caused enormous waste of 
urban freshwater resources and great loss of people's assets. 
As a result, it is an important and exigent task to establish 
dynamic management system of fundamental pipelines 
graphics, reinforce the management of fundamental pipelines 
map, improve the technical means of repairing and surveying 
pipelines map and guarantee the accuracy, integrality and 
actualization of the maps.