International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B2. Istanbul 2004 
  
  
    
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Figurel. The concept of the REAL TIME GIS 
3. CONTROL POINT FOR CONVERSION 
Geographic Survey Institute of Japan (GSI) adopted GRS80 
instead of BESSEL ellipsoid since April 2002. Parameters of 
WGS-84 for GPS and ITRF94 are almost equal to GRS80. By 
modification of geodetic system, the data of the past survey 
which uses Tokyo Datum will need to be changed to JGD2000. 
GSI opened the website for the conversion parameters and 
programs (TKY2JGD). GPS data almost corresponded to 
digital BM data in small-scale map, however, the parameter 
could not adopt in large-scale map. It is necessary to make the 
parameter in narrow area, because it was too large for the range 
which made parameter by TK Y2JGD. 
In order to calculate parameters, the control point was made 
using GPS by us. In the research, control point means the point 
which shows both coordinates of Tokyo Datum and JGD2000. 
The verification area has the accurate data of Tokyo Datum 
duse 
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(based on BESSEL ellipsoid and rectangular plane coordinate 
system) and was generated for town planning recently. There are 
89 coordinate points in a map (about 400m square) for the group 
of town planning work, we chose 14 points suitable for GPS 
positioning. GPS positioning was carried out from August to 
October in 2003. Static positioning was performed over 2 hours 
using GPS at the point, and the coordinates JGD2000 was 
obtained. Table | shows the positioning point number, the 
coordinates of Tokyo Datum and GPS positioning data. GPS 
positioning area is shown in Figure 2. 
The conditions which choose the positioning point are as 
follows. 
Clearly and confirmed point were used. 
The position need open sky and no high buildings. 
In this way, these 14 points which had both geodetic systems 
were used for conversion to JGD2000. 
  
  
Figure 2. GPS positioning area 
40 
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