Research On Key Technologies Of UAV Photogrammetry System For Class ? Survey Of Forest Resources

UAV photogrammetry system refers to a data acquisition and processing platform,which takes aerial images with high overlap from the air to the ground and gains a series of applicable results through data post-processing software.UAV photogrammetry system has become a new hot spot for application and promotion in the area of survey of forest resources on the strength that it is characterized by low cost,simple operation,short operation period,flexibility and timeliness.Class ? survey of forest resources is the largest and most standardized operation in the survey of forest resources.Since the ordinary surveying and mapping photogrammetry and the business points focused in Class ? survey of forest resources are quite different,there are the following problems when surveying and mapping UAVs are directly used to deal with the business of Class ? survey of forest resources:(1)with regard to hardware,ordinary surveying and mapping UAVs cannot be equipped with professional equipment for forest survey such as electronic angle gauges,and cannot collect forest survey factors under the forest;(2)in respect of data processing,although the post-processing software of ordinary surveying and mapping UAVs can yield high-precision surveying and mapping results,the process flow is complex,the data processing cycle is long,and the performance requirements of data processing equipment are high,so it is impossible to generate the subcompartment mapping base map with portable equipment in the field survey site and immediately apply it to the actual needs of the subcompartment survey;(3)as far as algorithm is concerned,the forest aerial photography is chiefly about canopy information,with multiple texture details,and there are a lot of non-rigid changes between image pairs as a result of airflow.When the aerial stereo images of forests are processed with ordinary surveying and mapping photogrammetry software,there often appear such problems as long time of feature matching,high error matching rate,poor quality in location distribution of successful matching points and so on.In this paper,a prototype of photogrammetry system for Class ? survey of forest resources is designed and implemented by means of open source technology.On the hardware side,the navigation function of ground station is realized,which is close to the canopy and goes deep into the canopy gap longitudinally,with the aid of ultrasonic and laser ranging sensors.With respect to software,(1)the AKAZE characteristic operator is upgraded with the help of VDVI,which improves the problem of high mismatch rate of aerial stereo images of forests;(2)a zoning matching strategy for aerial stereo images of forests based on POS constraint is put forward,which increases the matching speed of aerial stereo images of forests and the position distribution quality of successful matching points;(3)the subcompartment mapping base map is quickly generated by POS difference without control points,which addresses the problem that ordinary photogrammetry software can not quickly obtain the subcompartment mapping base map in the field.Besides,for the prototype of UAV photogrammetry system for Class ? survey of forest resources implemented in Daxing'anling forest region of Inner Mongolia,image acquisition,3D point cloud,DSM,DEM,DOM generation,extraction of tree number,segmentation of tree crown,extraction of tree height,estimation of unit volume and other application tests are conducted,which has verified the reliability of the system.This paper has endowed certain reference significance for designing and developing the UAV photogrammetry system of forestry,exemplary significance for deeply combining UAV and forestry business,and certain exploratory significance for enhancing the automation and intelligence of forest monitoring equipment.