偏冠对树冠垂直投影面积计算的影响

Effect of Partial Crown on Calculation of Vertical Projection Area of Crown

[目的]针对树冠结构复杂、形状不规则等问题,实现树冠垂直投影面积自动计算并提高树冠投影区域面积计算精度。[方法]以研究区453棵杉木为研究对象,精确测量每木8向冠幅。以Visualstudio和ArcGIS混合编程,进行树冠测量半径的坐标转换,采用Bezier曲线进行边界平滑,实现树冠垂直投影面积自动提取,并与传统计算方法进行对比分析。利用“圆度”来衡量树冠偏冠,并计算树冠偏冠指数与树冠垂直投影面积计算的相关性。[结果]本研究提出的树冠垂直投影面积计算方法能够计算出树冠真实面积,计算过程中测量冠幅半径数量越多,计算结果越接近真实冠幅面积,相比于椭圆的计算方法,把树冠视为正圆所得面积更接近真实面积。不同树冠垂直投影面积计算方法的结果和树冠垂直投影面积差值与树冠偏冠指数呈显著正相关。[结论]基于树冠投影区域形状的面积计算相较于传统的面积计算方法更加准确,为林业遥感冠幅提取精度验证提供了一种新思路。

[Objective]Aiming at solve the problems of complex structure and irregular shape of tree crown to realize the automatic calculation of vertical projection area of tree crown and improve the calculation accuracy of projection area of tree crown.[Method]A total of 453 Cunninghamia lanceolata trees were selected in the study area,and the crown width of each tree in 8 directions were accurately measured.Visual studio and ArcGIS mixed programming were used to convert the coordinates of the measured canopy radius.And the Bezier curve was used to smooth the boundary,so as to realize the automatic extraction of the vertical projection area of the tree crown,and the results were compared with that of the traditional calculation method.The"roundness"were used to evaluate the crown partial crown,and the correlation between the partial crown index and the vertical crown projection area were calculated.[Result]The method proposed in this paper can calculate the real canopy vertical projection area.The result indicates that the more the measurements of crown radius during calculating the canopy vertical projection area,the closer the calculation result to the real crown area.Compared with the ellipse method,the area obtained by treating the crown as a circle is closer to the real area.It is also found that,there is a significant positive correlation between the results of calculating the crown vertical projection area with different methods and the difference of the crown vertical projection area and the crown deviation index.[Conclusion]The area calculation method based on the shape of the canopy projection area is more accurate than the traditional area calculation method,which provides a alternative idea for the verification of forestry remote sensing crown extraction accuracy.