Research On Terrain Feature Extraction Algorithm

Valley and ridge are important basics for humans to master terrain information,which are of great significance for the study of landform and physiognomy.Therefore,it is very necessary to extract the valley line and the ridge line from the gray topographic map for the modern analysis of the topography.However,for the existing algorithm for extracting valley and ridge lines,the biggest problem is that it is impossible to determine whether the current point is a candidate point for the topographic feature line.Besides,there are too many candidate points for the extracted ridge line and valley line in a certain range,so the time it takes is excessive.To solve the above problems,this paper proposes an improved algorithm based on PPA(Profile Recognition and Polygon breaking Algorithm)to extract ridge and valley lines.The main characteristics of the algorithm are that it is simple to use,does not involve complex mathematical formulas,does not involve complex matrix changes and can consider terrain feature information in a global range.It can also preserve relatively small branches of feature lines so as to extract a more complete terrain feature line.The main work and summary are as follows:1.The thesis in-depth analysis the basic principle and design process of the existing PPA algorithm in detail.It uses MATLAB to simulate.Based on the experimental results,it analyzes the problems existing in the original algorithm in screening candidate points and pruning process.2.Aiming at the problem that the original PPA algorithm filters the valley candidate points too loosely and has too many redundant points,it proposes a new screening method,changes the screening conditions,effectively reduces the redundant points of the valley candidate points,and makes the whole algorithm The time overhead is reduced.3.The decisive factors of pruning are modified during the pruning process.The number of pruning is no longer half the length of the profile,but is determined by the size of the sampling interval step,in which way relatively small branches can also be extracted.4.In-depth analysis of the time performance and the final results of the improved algorithm before and after,which proves the rationality of the improved algorithm.5.The paper tests the improved algorithm from different contour lengths,different screening conditions,different sampling distances and different pruning times.It also analyzes the experimental results in detail and validates the effectiveness and rationality of the improved algorithm.By comparing the experimental results,it is found that the improved algorithm is far more time saving than the original algorithm,and it can not only extract the main branch of the terrain feature line,but also can extract the relatively small branch branches that the original algorithm can not retain.Therefore,the improved algorithm is better than the original algorithm in terms of time efficiency and extraction effect.