The graphical cadastral maps, which were created as part of Land Survey Project in the 1910s, are still in use despite their low accuracy as the land boundaries are presented in dots and lines on paper plans. The year of 1975 marked the beginning of n...
The graphical cadastral maps, which were created as part of Land Survey Project in the 1910s, are still in use despite their low accuracy as the land boundaries are presented in dots and lines on paper plans. The year of 1975 marked the beginning of numerical cadastre in large land development projects to solve the problem. A numerical cadastre registered land boundary points in coordinates. In 2012, the Cadastral Resurvey Act was enacted as a national project to solve the issue of land of cadastral non-coincidence, which accounted for approximately 14.8%. Since then, the plan digitization project has been in progress. Another plan is being made to convert geographical cadastral maps into numerical ones in lots of cadastral non-coincidence. There have been remarkable technological advancements from the old plane table survey to the current total station-based electronic plane table survey and GPS survey. The survey errors due to plan extension and wear are gradually solved by the plan digitization project. Control points, which are the most important element in survey, are still mostly buried in roads that guarantee easy intervisibility and observation. Control points in the roads are, however, in a high risk of loss due to pavement, waterworks, and drainage works and accordingly require considerable maintenance costs.
This study thus set out to set roof edges of high-rise buildings, tips of ventilations on the rooftop, and tips of steel towers as control points of direction coordinates to prevent the loss of control points as they posed a low risk of loss and secured a clear view. It also aimed to propose the validity of cadastral survey with such control points of direction coordinates based on the observations and calculations at those control points. The investigator assumed the current cadastral control points and lot boundary points that had been announced as true values and compared and analyzed the accuracy of cadastral survey based on direction coordinates with the direction coordinate-based T/S survey and network-RTK survey methods.
First, the study tested X and Y coordinates that were generated by selecting, observing, and calculating control points of direction coordinates, which were found at the rooftops of buildings, tips of ventilators, and tips of steel towers, which posed a low risk of loss and no possibility of changes. Forward intersection was used to calculate the coordinate values of selected reference points of direction coordinates. The investigator drew a direction line by collimating the objects selected as direction coordinates at the cadastral control points of three points or higher and identified the points where direction lines were crossing each other based on the reference point values(X and Y) of direction coordinates, which were tested in backward intersection. After installing a machine at the current cadastral control points that had been announced, the investigator obtained the X and Y coordinate values of station marks by applying backward intersection(three points) to the control points of direction coordinates, which were then tested by comparing the coordinate values of announced cadastral control points with the X and Y coordinate values obtained by applying backward intersection to direction coordinates.
Secondly, all the control points and lot boundary points in the subject areas were observed in backward intersection(three points) based on the control points of direction coordinates as well as the network-RTK survey method. The experiment compared and analyzed X and Y coordinate values obtained in those two experimental methods as well as the announced cadastral control points that were assumed as true values and the lot boundary point coordinates registered in Registry of Boundary Point Coordinates, thus demonstrating the accuracy of direction coordinate reference point-based survey method.
Finally, the investigator analyzed the actual states of control points in Gwangju, Gyeonggi Province for the last three years and conducted analysis of current states of reference points and also installation and re-installation costs for control points, thus carrying out cost-benefit analysis of utilization of direction coordinate reference points with a relatively low risk of loss.
The utilization of control points of direction coordinates proposed in the study, however, requires intervisibility between the random station marks and the control points of direction coordinates. It will be thus difficult to apply them to downtown areas with a concentration of high-rise buildings, and there is a need for in-depth researches according to local characteristics.