Distance to tree
The measurement of distances is usually required for the measurement of tree height along the trigonometric principle. But it is obviously also needed for various other purposes, such as laying out sample plots or measuring the position of trees. Especially for permanent plots the measurement is needed and also recorded.
It is important to keep in mind that for practically all purposes we need to determine the horizontal distance. On sloped terrain, an accordant slope correction has to be done. Modern electronic range finders that use ultrasonic or laser technique do usually also measure the slope angle so that they can directly provide the horizontal distance.
If such devices are not at hand and only the oblique distance can be measured, for example by a distance tape or by counting steps or by the simple optical devices that are in some height meters (Blume-Leiss, Suunto), we also need to measure the slope angle \(\alpha\) and to apply the known slope correction factor \(cos(\alpha)\) in any case.
