Abstract:
This research aim is to study the horizontal position accuracy of the maps through internet service
and to conduct the feasibility of application of satellite through internet service, to update the maps in
multi scales.
Testing of the position accuracy is based on standards of Federal Geodetic Data Committee 1 9 9 8
(FGDC 1998). In the testing, 28 horizontal control points is tested and the testing area is divided into four
sections, quadrant. Each quadrant consists of less than 6 points of 20 percent of all 28 points. Those point
location are required to distribute regularly. Distance between points is not less than 10 percent of the
distance along the diagonal line (d) of the test area with 27 by 27 square km. Positioning of the horizontal
coordinates of the points is by fast static technique with two frequency GPS receivers. Later, post
processing is conducted on TGO (Trimble Geomatic Office) under C-class order standard of GPS
position surveying with 10 part per million or ppm. The coordinates of the test point by the GPS surveying
as the reference are compared to the coordinates of the points displayed on the internet. This comparison
is to calculate the horizontal accuracy by statistics techniques, Root Mean Square Error (RMSE) following
National Standard for Spatial Data Accuracy (NSSA), USA
The results indicated that the map through Internet Service has east wad1.88 meter and northward
1.80 meter standard deviation as well as 4.5 meter horizontal accuracy with 95 percent confidence level.
Also In terms of application of map updating, the figure of accuracy from the testing shows the map on
the internet would be suitable for map updating and revision at 1:22500 map scale or smaller because the
accuracy from the testing is satisfied with the specification of map revision with 1:10000 scale, Class II.
This specification endorsed by the Mapping Division, Royal Thai Survey Department requires 5 meter
accuracy for 1:10000 scale or smaller . For oceanographic surveying the testing result shows the map
would be suitable for map information updating and revision at 1st Order Class with 5 mater-+5 % of
water depth. Also it would be applicable for map updating and revision at 1:5316 map scales or smaller
with satisfaction of the standard United States National Map Accuracy Standards.