Terrain Simulation Accuracy Evaluation Of Permanent Gully Based On Point Cloud Sampling Spacing And Interpolation

Accurate permanent gully(PG)morphology is great significance for revealing its evolutionary mechanism,the digital terrain accuracy of PG is the key to extract parameters,but the point cloud sampling interval of PG and interpolation algorithm are the main influencing factors of its terrain accuracy.At present,the related PG terrain simulation research generally compares the accuracy of the same point cloud interval and the accuracy difference of different interpolation algorithms,and does not take the both into consideration.Based on,this paper discusses the accuracy difference of DEM construction of PG by the combination of point cloud sampling distance and spatial interpolation algorithm,which is helpful to provide reference for its terrain simulation.At the same time,high-precision DEM is also the key to extract parameters.In January 2017,two typical PG(U-shaped and V-shaped cross-sections)were selected in Yuanmou's dry and hot valley area,and the initial spacings of 0.04 m and 0.15 m were set according to the channel size for 3D laser scanning sampling;and then based on CloudCompare software performs equidistant and random thinning of the original point cloud,uses the point cloud of the two thinning modes to generate DEM,and evaluates its accuracy,compares the differences of thinning modes,and then selects the best method of point cloud thinning.After that,point cloud elevation is interpolated by using common Kriging interpolation(OK),inverse distance weighted interpolation(IDW),radial basis function(RBF)and high-precision surface modeling(HASM)to generate different DEM.Based on the validation data set,the interpolation error is analyzed by using standard deviation(SD),root mean square error(RMSE)and average absolute error(MAE)index to determine the interpolation error.Finally,based on the optimal interpolation results of Ushaped and V-shaped PG,taking the cross-section,longitudinal section and volume parameters as the starting point,the morphological differences of other interpolation results are compared,so as to prove the impact of topography accuracy of erosion gullies on morphological extraction.The main conclusions are as follows:(1)The precision of PG constructed by equal distance thinning is higher than that by random thinning.When the number of point clouds is equal,the standard deviation(SD),root mean square error(RMSE)and average absolute error(MAE)of the point cloud thinned by U/V-gully are smaller than those of the point cloud thinned by random.In addition,the interpolation error of point cloud increases with the increase of point cloud distance,that is to say,the DEM accuracy of erosion gully decreases with the increase of point distance.(2)The interpolation accuracy of 0.04 m interval point cloud in U-gully is the best by using high-precision surface modeling algorithm,and that of 0.15 m interval point cloud in V-gully is the best by using high-precision surface modeling algorithm.The analysis of interpolation accuracy of U-gully training samples and test samples shows that the standard deviation,average absolute error and root mean square error of HASM-OK are the smallest under the same spacing and different interpolation methods,and the interpolation error of point cloud with 0.04 m spacing is the smallest under the same interpolation method and different spacing.Similarly,for the interpolation accuracy analysis of V-gully training samples and test samples,the HASM-RBF method has the highest interpolation accuracy when the point distance is the same;when the interpolation method is the same,the terrain error of 0.15 m interval point cloud construction is the smallest;while the original resolution point cloud has the smallest error in different interpolation methods.(3)The HASM optimization algorithm can significantly improve the accuracy of ordinary interpolation algorithm.For U/V-gully point cloud,the interpolation accuracy optimized by HASM-OK,HASM-IDW and HASM-RBF is significantly higher than that of OK,IDW and RBF,and the error amplitude increases with the increase of point cloud spacing.(4)The accuracy of DEM has a great influence on the extraction of channel shape parameters.Based on the shape parameters extracted by the optimal interpolation combination,the deviation of other gully shape parameters increases with the decrease of interpolation combination accuracy.On the whole,the DEM precision of erosion gully has little influence on the extraction of gully width(W),while the deviation of gully depth(D)extraction increases with the decrease of DEM precision.In the same way,the lower the DEM accuracy of erosion gully,the more the terrain information lost in the longitudinal direction of gully,and the greater the deviation of its length(L)extraction.For the volume calculation of erosion ditch,the lower the DEM accuracy is,the smaller the volume of gully is.