Tham khảo luận văn - đề án 'báo cáo lâm nghiệp: "wedge prism as a tool for diameter and distance measurement"', luận văn - báo cáo phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | JOURNAL OF FOREST SCIENCE 54 2008 3 121-124 Wedge prism as a tool for diameter and distance measurement L. SÁLEK D. Zahradnik Faculty of Forestry and Wood Sciences Czech University of Life Sciences Prague Prague Czech Republic ABSTRACT The wedge prism which is generally used for the measurement of basal area in diameter at breast height is also a tool for the measurement of distance as well as for the measurement of diameters at a certain height of the stem in the upper stem. Measurements using the wedge prism are based on the same principle as measurements using Bitterlich mirror relascope. This method is appropriate for non-destructive determination of stem volume. Moreover the wedge prism can be used for the sorting of logs in standing trees when the small end of expectant assortment has to be known. As the wedge prism is a common tool for foresters its usage seems to be larger than only the measurement of basal area. Keywords wedge prism upper stem diameter measurement distance measurement log sorting The wedge prism is a widely used small tool for the measurement of basal area mainly in diameter at breast height dbh . It is one of the tools based on the method invented by the Austrian forester Bit-terlich Korf et al. 1972 . The principle is an angle counting of stems using the ratio of the diameter to the distance between the measured stem and the observer the centre of the sample plot . There are two ways of projecting the angle - By prolonging two lines of sight from the eye through two points whose lateral separation is fixed both of which are in the same horizontal plane and both of which are at the same fixed distance from the eye Husc et al. 2003 - By deviating the light rays from the tree through a fixed angle wedge prism . The principle is that the given ratio between widths at a certain distance from the eye. The ratio is determined with an angle gauge according to the trigonometric function see Fig. 1 . a a a 2arctg -b 2arctg2OT To calculate the .
