Indirect Generalization of Contours Using Importance Sequence of All Points
Objectives:In the generalization method of contours,the indirect generalization of contours based on three dimension(3D)Douglas-Peucker(3DDP)algorithm has a good application prospect.This method achieves the purpose of deleting the sub-points of the surface and reserving the main points by set-ting thresholds,but this threshold updating method affects the efficiency of indirect generalization of con-tours,and there is no consideration of the semantic characteristics of surface points in selection.Methods:Aiming at above problems,we presented an indirect generalization method for contours using the impor-tance sequence of all points,and topographic feature lines considering terrain slopes extracted by an optimal position convergence method were taken as constraints of generalization.First,data was converted into 3D discrete points and sorted.Second,no points were deleted,and the importance of geometric weight and se-mantic weight of all discrete points was calculated to form an importance sequence which ordered all points from the largest to the smallest important values.Finally,according to the generalization target scale,the reserved points in the importance sequence were determined to achieve the indirection of contours.Results:Experimental results show that before the point selection method is improved,it takes about 18 minutes to select points by setting thresholds every time,which affects the generalization efficiency.However,the pro-posed method only takes about 25 minutes to queue all points by their importance values.Besides,by adding semantic information,the topological variation of generalized contours is reduced.Conclusions:The pro-posed method can not only improve the efficiency for the indirect generalization of contours,but also effec-tively prevent the topological variation of contours.
three dimension Douglas-Peucker algorithmtopographic feature lineimportance sequence of pointsindirect generalization of contours
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