一個LiDAR DTM 的可靠度指標及其初步測試

This paper designs and proposes a simple reliability index ξ of LiDAR DTM. A ξ-value (0 ≤ ξ ≤ 1) is computed for each grid point of LiDAR DTM. The so-called "reliability" is an index to express to what extent the data is reliable. A higher ξ-value denotes that the grid point has a more reliable elevation. ξ = 0 indicates that the elevation of the grid point is unreliable because there is not any LiDAR terrain point inside the topography correlation area. After further study is completed in the coming years and the applicability of reliability index for LiDAR DTM is confirmed, the Ministry of Interior (MOI) is strongly suggested to supply the 3D ground coordinates (X, Y, Z) and a proper reliability index value of each grid point in a LiDAR DTM to users so that users can know which grid points have reliable elevations. Our preliminary test results demonstrate that the elevations of grid points in steeper areas will have larger errors, if they have the same ξ-values. In the case with 0.6 ≤ ξ ≤ 0.8, the elevation difference dZ between check data and computed data by LiDAR terrain points ranges from -10.44 m to 12.68m for those grid points in the areas with the slope level 1 and 2. For those grid points in the steepest areas with the slope level 4, their dZ-values range from -19.12 m to 12.28 m. High resolution, namely 1mx1m, LiDAR DTM and its original data of LiDAR terrain points are not available due to our national regulations. Moreover, acquisition of ground truth data in study areas is difficult and time-consuming. Therefore, the study results fail to meet our expectation. Nevertheless, it would like to inspire each and every one of you to consider the reliability of LiDAR DTM an important index. Also, the Ministry of Interior is strongly suggested to start the related researches and developments in order to be able to then safeguard the safety of people's lives and property.