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Ground seed detectors and interpolation methods are fundamental components of filtering algorithms. However, the performance of different detectors and interpolation methods typically varies, and few studies have been conducted on the adaptability of different detectors and interpolation methods to different terrains. Therefore, we compare three ground seed detectors (cylindrical neighborhood (CN), fixed grid (FG), and moving window (MW)) and three interpolation methods (triangulated irregular network (TIN), thin plate spline (TPS), and inverse distance weighting (IDW)). In addition, nine filters are constructed by combining the three ground seed detectors and the three interpolation methods to evaluate their comprehensive influences. To assess the performance of these detectors, interpolation methods, and filters, fifteen ISPRS-supplied light detection and ranging (LiDAR) benchmark datasets are utilized in the experiment. The findings indicate that the CN-TPS filter, which combines the CN detector and TPS method, achieves superior performance across mean Pg (99.16 % – correctly classified ground points divided by all extracted ground points), RMSE (0.44 m – root mean squared error), and total error (3.78 %). Moreover, the filtering methods are mainly affected by the performance of the ground seed detector and are less affected by the selected interpolation method. These results can be used to provide a valuable reference for designing an optimal LiDAR filtering algorithm for varied terrain types and applications.

Introduction: Many individuals test positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA after recovering from the coronavirus disease (COVID-19), but the incidence of reactivation is unknown. We, therefore, estimated the incidence of reactivation among individuals who had recovered from COVID-19 and determined its predictors. Methods: In this retrospective cohort study, patients with COVID-19 were followed up for at least 14 days after two consecutive negative SARS-CoV-2 polymerase chain reaction test results obtained ≥24 h apart, and the frequency of SARS-CoV-2 reactivation was assessed. Results: Of the 109 patients, 29 (27%) experienced reactivation, and seven (24%) of these were symptomatic. The mean period for the real-time PCR tests for SARS-CoV-2 from negative to positive results was 17 days. Compared with patients without reactivation, those with reactivation were significantly younger and more likely to have a lymphocyte count of