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

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.