Measurement and precision analysis of tree height by 3D forward intersection

Because of hypsography, the horizontal distance between the station and the target tree cannot be measured easily by tape or stadia in forest survey to calculate the tree height with triangular surveying. In order to solve this matter, the authors applied the forward intersection to survey tree height. The content of the forward intersection is to construct a triangle with two stations and target tree, measure the distances between the two stations and three angles, then get the distance between one station and the target tree by law of sines, finally the perpendicular direction angle is measured, and the tree height is calculated. Theodolite and compass are used broadly in forest survey. Precision analysis and experiments demonstrated that the relative precision of tree height was less than 5% with theodolite and overrun 5% with compass. The precision of theodolite can satisfy the application in forestry. A conclusion is drawn that forward intersection can be taken in measuring tree height with theodolite.