Extraction of Individual Tree Crown based on UAV Tilt Photogrammetry
Compared with the traditional manual field survey method,the use of UAV tilt photogrammetry tech-nology for multiangle photography to extract individual tree crown information has the advantages of high effi-ciency,accuracy and low cost.In this study,an individual tree crown extraction method combined with a visible vegetation index and watershed algorithm was proposed by taking a larch near-mature forest in the Wangyedian forest farm in southwestern Karaqin Banner,Chifeng city,Inner Mongolia,as the research object and using UAV images obtained by tilt photogrammetry as the data source.First,the Excess Green minus Excess Red(ExGR)in the visible light band was calculated by a digital orthophoto model.The median filter was used to de-noise the tree crown area map,and a reasonable threshold was selected to binarize the image to separate the veg-etation and non-vegetation areas.Vegetation areas were used to mask the canopy height model.Finally,the ac-curacy of individual tree crowns was verified by the watershed segmentation algorithm.In the process of extract-ing the crown area,vegetation and non-vegetation areas are successfully separated based on the ExGR index and threshold method.Through median filtering,speckle and noise caused by uneven brightness,shadow and texture in the non-vegetation area are effectively removed,the integrity of the crown edge and the connectivity of the crown are ensured,and the over segmentation phenomenon of the watershed algorithm is reduced.At the individual tree scale,the accuracy rate of crown parameter information extraction was 88.72％and 79.38％,the recall rate was 93.29％and 88.60％,and the F-score was 90.59％and 83.74％.On the sample plot scale,the relative errors are 15.45％and 22.92％respectively.The results show that the visible vegetation index based on Digital Orthophoto Image can effectively eliminate the influence of bare land and other background factors in the forest,and the watershed segmentation algorithm based on the canopy height model can accurately distinguish individual tree information.The combination of the two data sources based on the UAV tilt photogrammetry technology gives full play to their respective advantages.The method of extracting the single tree crown informa-tion based on the UAV tilt photogrammetry technology is feasible and can extract the single tree crown informa-tion of the forest with high canopy density efficiently and accurately.
Tilt photogrammetryIndividual tree crownVisible vegetation indexThreshold segmentationWatershed segmentation
NETL
NSTL
万方数据
维普
