According to the relevant laws and regulations, the government and the local are required to carry out surveys on national/public land at least once a year. However, since most surveys are based on field surveys depending on the naked eye, there is a problem in grasping accurate occupancy status. In order to solve this problem, The cadastral surveying has been carried out, but it is difficult to survey completely all of the nation/public land in the country due to human and material limitations. In order to overcome these limitations, this study proposes a survey method of Utilization of UAV and in order to evaluate the efficiency, we carried out the comparative evaluation of the cadastral surveying in terms of information acquisition, quantity and quality of information, economical efficiency, and simplification of processing steps.
The accuracy of the orthoimage is 0.076m at the maximum RMSE of the UAV orthoimage check point and 0.042m at the minimum RMSE compared with the VRS-GNSS performance. When the allowable error specified in the Implementing Regulation of the current cadastral survey is applied, the 0.36m tolerance corresponding to the scale of 1 / 1,200 is satisfied.
The accessibility of the survey site and the availability of monitoring, which are detailed items of information acquisition, were comparatively evaluated in detail. In terms of the accessibility of the survey site, UAV orthographic image can be used to survey national/public land even if the surveyor does not directly approach the survey site. However, since the surveyor must approach the survey site directly, It is difficult to carry out survey on national/public land by cadastral surveying.
As using UAV, national/public land can be monitored at all times by periodic orthoimage acquisition. However, it is difficult to conduct time series analysis in terms of survey on national/public land by cadastral surveying.
The broadness of the information, the interpretation of the data and the combination with various spatial information, which are detailed items of the quantity and quality of information, were comparatively evaluated in detail. UAV is able to acquire the information of location, area, land use status of the survey site and surrounding area at the same time in one flight, because the area of the individual photographs taken from the vertical vantage point is about 23,000㎡. But in terms of the cadastral surveying, the horizontal vantage point, the maximum distance of information that can be acquired at one point is only about 300m because the cadastral point of reference is between 50m and 300m. In other words, cadastral surveying is relatively inefficient in the broadness of the information.
In the interpretation of the data, it is difficult to understand the cadastral survey data intuitively for nonspecialists of cadastral survey, while UAV orthographic images are image data that anyone can understand intuitively, even if they are not experts in cadastral surveying.
In combination with various spatial information, orthographic images and continuous cadastral maps were overlapped to grasp the state of occupation of the national/public land. As a result, the ratio of occupied national/public land to national/public land of study area was 4.3% and the ratio of parcel number was 44.7%. As such, UAV orthographic images can be combined with other spatial information unlike cadastral survey information.
In terms of economical efficiency of surveys on national/public land, it is 40,470,000 won when calculating the cadastral surveying fee of 213 parcels occupied within 1.9㎢, while the cost of UAV orthophotograph production in the region is 13,972,564 won. UAV utilization method is 26,497,436 won cheaper than cadastral survey method. In terms of economic efficiency, UAV is considered to be economical when surveying national/public land.
In terms of the simplification of the processing steps, UAV based surveys on national/public land can be simplified to 5 steps in 8 steps of surveys based on cadastral surveying. Therefore, it can be partially solved the problems of the time shortage due to the complicated procedure of the work, which is one of the problems of the surveys on national/public land.
In conclusion, UAV is superior to cadastral surveying at the surveys on national/public land in terms of the ease of obtaining information, the quantity and quality of the information acquired, the economy, and the simplification of the processing stage. Therefore, the UAV can be applied without any problem to the surveys on national/public land, and it is urgent to improve the law in related fields to accommodate it. In this study, the effectiveness of UAV in the surveys on national/public land was evaluated by considering only the four items mentioned above, but more objective items could be needed to consider.