Quality Control Method for Filtering in Aerial Lidar Survey

The purpose of filtering LIDAR data is to extract the laser points which are truly reflected from the bare ground. However, the results obtained may vary since several engineers are involved in the manual filtering process. For this reason, the QC/QA maps are created in Japan after the filtering process in order to control the filtering quality. This paper describes a quality control method using an original and a unique QC/QA maps. We use two types of QC/QA maps to check the filtering results: one is a color-shaded relief map and the other is our monochrome-shaded point maps. The reason we use two types of QC/QA maps is that they have different purposes. The purpose of color-shaded relief map is used to inspect the detailed noise data. In contrast, the purpose of a monochrome-shaded point map is to examine the over-elimination of point clouds during the filtering process. Using these two types of maps together, we are able to extract from the point clouds obtained by airborne LIDAR that are truly reflected from the bare ground. Finally, we have carried out image analysis of monochrome-shaded point maps to automatically extract the erroneouslyeliminated points from the point clouds. Some results of automatic extraction are also reported. This quality control method will certainly improve the quality of the filtering process for the airborne LIDAR points. The method described can be applied not only to airborne LIDAR but also to terrestrial laser surveys. However, more study on the automatic examination is needed in the future, and some considerations regarding to the automatic examination are also described in this paper. Green line: Auto-Filter Red line: Auto-Filter and Manual Filter Figure 1. Cross section 2.1 * Corresponding author.