数字近景摄影测量用于森林固定样地测树的研究

Forest measurement in fixed sample plot by digital close-range photogrammetric survey.

该文以普通的光学或数字相机为工具 ,借助计算机建立数字近景摄影测量系统 .系统通过普通相机对固定样地摄影 ,建立以内、外方位元素 (x0 ,y0 ,f;XS,YS,ZS,ω ,k ,φ) 为未知数摄影测量共线方程 ,通过DLT变换 ,求得待定参数 ,进而把像方空间和物方空间联系起来 ,借助计算机系统 ,就可确定像方任一点坐标 (x,y)对应的物方坐标 (X ,Y ,Z) ,从而恢复物方空间立体 ,计算胸径、任一处直径、树高、树冠体积等测树指标 .这种系统不需要像控点就能建立待测目标的数字模型 .实验结果表明 ,通过此摄影测量系统可测量树高、胸径、树冠体积等 ,树高测量的相对误差为 2 % ,胸径测量的外符合误差为 1% ,树冠体积的内复合误差为 3% .

A digital close-range photogrammetric surveying system is set up with the aid of optical or digital camera and computer. The system establishes the photometric surveying collinear equation, in which the interior and external orientation elements (x0, Y0, f; Xs, Ys, Zs, ω, κ, φ) are regarded as unknown factors, through photographing the fixed sample plot with the common camera. Then the parameters are worked out with the method of DLT transformation to connect image space with object space. With the aid of computer system, the coordination (x, y) of any random point in image space and the corresponding one (X, Y, Z) in object space are made certain to restore the stereoscopic model, and to calculate the surveying index such as diameter at breast height, diameter at random height, tree height and crown volume etc. Without the photographic controlling point, the system can establish the digital model for the target trees. The experimental results indicate that the relative measurement error of tree height is 2%, the outer accord one of breast diameter is 1% and the inner composite one of volume of crown, 3%. So the method can be proved to be used for measurement in forest fixed sample plot.