C.X. Zhi Faculty of Electrical Engineering
Universiti Teknikal Malaysia Melaka, Malaysia
chan_xin_zhihotmail.com Keywords: Laser, Diameter, Tree
Abstract
This paper presents a study on the accuracy of laser range finder system for the measurement of tree’s diameter. The study has been conducted by using Hokuyo URG-04LX-UG01 Laser Range Finder. The measurement was
done in different distances from the measured tree at a fix elevation in two different modes; sensor held in hand and sensor mounted on a tripod. An algorithm was developed to derive the formula for calculating the diameter
by applying the principle of circle tangent theory. The results obtained are the values of accuracy for the diameter measurement of a tree for different distances between the sensor and the tree measured which are
presented in graphs. Finally the accuracy levels between the two modes are compared to find the most preferable mode for the measurement in real application.
1. Introduction
Contact and non-contact measurement devices have been developed for decades to measure the diameter of a tree. These devices are still considered to be time consuming and low in accuracy while forestry and plantation
workers are still using one of these methods for diameter measurement. Fast responding and accurate non- contact measurement device is in need for this kind of measurement in order to reduce the time for measurement
of the whole plantation. Thus an accurate measurement device is required to determine the correct time for fertilization and time to tap off the trees measured.
Available methods used to measure diameter of tree do not consist of Graphic User Interface GUI, time consuming and low in accuracy. This causes difficulty for forestry workers or researchers as well as affecting
the result of measurement values. Rubber Industry Smallholders Development Authority RISDA is one of the estate developers in Malaysia who faces difficulty when dealing with problem in measuring circumference of
tree trunk. This is caused by massive amount of rubber trees to be measured using difficult and low accuracy measurement methods such as tape measuring, calipers and Biltmore Sticks. In order to eliminate these
problems, alternative method is researched to measure tree diameter together with the study of its performance in term of accuracy.
Previous researches have been done which involves measurement of tree’s diameter and circumference. Researchers from the US Department of Agriculture have come out with Criterion Laser Instrument which
employs laser beam to measure tree diameter [1]. Despite considering its high cost, this device requires user to manually entering the tick marks across the tree and distance from the tree into the keypad to calculate the
diameter of the tree which is then required for further analysis.
Another research was previously done by researchers from Universiti Teknikal Malaysia Melaka regarding the linear and rotary infrared scan system for the circumference measurement of trees [2]. This measurement
system resulted in poor performance due to the step angle resolution of stepper motor used. Larger angular resolution results in bigger approximation for analog linear scan method. There was also an issue related to the
limitation of IR sensors used as these sensors gave unstable results. Therefore another sensor that employs different light source, which is laser, is much preferable to replace the infrared as the measurement medium.
In this paper, we will further discuss on the measuring principle in Section 2. Section 3 describes the experimental setup used for the diameter measurement and finally in Section 4, we will thoroughly discuss the
results obtained from the experiments.2. Formatting your paper
2. Measuring principle
