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Method of Measuring Tree Height and Volume Based on CCD Smartstation

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Nature Environment and Pollution Technology p-ISSN: 0972-6268 Vol. 17 No. 4 pp. 1305-1313 2018 An International Quarterly Scientific Journal e-ISSN: 2395-3454 Original Research Paper Open Access Method of Measuring Tree Height and Volume Based on CCD SmartStation Yang Liyan*(**), Feng Zhongke*†, Liu Yingchun***, Liu Jincheng* and Sun Renjie* *Precision Forestry Key Laboratory of Beijing, Beijing Forestry University, Beijing 100083, China **School of Land Resources and Urban and Rural Planning, Hebei GEO University, Shijiazhuang, 050031,China ***Academy of Forestry Inventory and Planning, State Forestry Administration, Beijing 100714, China †Corresponding author: Feng Zhongke ABSTRACT Nat. Env. & Poll. Tech. Website: www.neptjournal.com Forest stock volume is an important factor for evaluating the status of forest resources and management level of the forest. It is also an important index to evaluate the ability of the forest to reduce the risk of Received: 31-01-2018 climate change. Standing timber volume is the basis for accurate assessment of forest stock volume. Accepted: 11-05-2018 In order to quickly and accurately measure the volume of standing timber and solve the problems and Key Words: shortcomings of the traditional measurement methods of volume, this paper presents non-contact and CCD SmartStation nondestructive method of measuring tree height and volume, which uses CCD as a measuring tool and Photogrammetry takes measuring principle of close-range photogrammetry as a basis. The method obtains the photograph Volume of standing timber by the CCD camera and the exterior element, when the photograph is shot by the total station’s Tree height goniometry and ranging function, and takes surface, which crosses the center of the tree and is perpendicular to the main optical axis of the camera, as the solution surface. Extracting coordinates of feature points of standing timber in the photograph, calculates diameter at any height of standing timber, which achieves measurement of height and volume of standing timber under the model of single-photo solution and multi-photo solution of correction and merging. In order to simplify the operational procedures of the field, through the observation of one pole and 160 standing timber, the optimal observation distance of this method is 15 m, and the optimal observation angle is 0°, and the accuracy of the single-photo mode is better than the multi-photo mode of correction and merging. The results show that the precision of tree height measurement method is 98.41% and the measurement accuracy of volume is 98.01%, which can meet the precision requirements of forestry investigation. This provides a new idea of data acquisition for the establishment of timber volume tables and forestry surveys, which is of some reference value. INTRODUCTION sive, destroying the forest and so on. Correspondingly, some researches have proposed to establish the non-destructive As one of the important global terrestrial ecosystems, for- estimation method of wood volume, such as high-elevation ests have always been an important way for people to access method, positive-type number method, experimental shape resources, maintain a good ecological environment and number method, shape point method and so on (Cao 2015, mitigate the impact of climate change. Forest stock volume Feng 2015). However, due to the cumbersome operation, is not only an important factor in evaluating the status of many restrictions and low measurement accuracy and other forest resources and the level of forest management, but unfavourable factors, the use of these methods are limited. also an important indicator to evaluate the ability of forests Therefore, scholars at home and abroad hope to establish a to reduce the risk of climate change. Therefore, the stock method of the non-destructive, rapid and accurate method volume has been one of the main factors in forest surveys to acquire the timber volume. Among them, the (Haibin 2016, Feng 2015, Liu 2014, Wang 2014, Guendehou representative studies include scanning and modelling of 2012). Forest stock volume is the sum of the volumes of all standing timber acquiring timber volume based on three- standing trees per unit area of forest (Vibrans 2015, Berger dimensional laser scanner, volume calculation by angle and 2014, Zeng 2015). Acquiring accurate standing timber distance measurement of the electronic theodolite and total volume is the basis for accurate assessment of forest stock station, volume measurement of monocular CCD digital volume and also the focus of tree research for a long time. camera and so on. However, these methods also have their The traditional timber volume measurement method is limitations. For example, 3D laser scanners are expensive also called trunking analysis method, that is, after cutting and cumbersome to operate; electronic theodolite and total the standing tree, doing the trunk analysis, but the method station measurement volume method need long hours of has the disadvantages of time-consuming and labour-inten- foreign work and intensive work. CCD digital camera 1306 Yang Liyan et al. method needs to place the calibration scale or the help of pares the current method of measuring timber volume with artificial measurement (Deng 2007, He 2016, Vonderach the method proposed in this paper (Cao 2015, Cao 2013, He 2012, Feng 2003, Wang 2013, Abramo 2007, Tompalski 2013). 2014, Yu 2016, Zhao 2014, Jiao 2013, He 2012, Straub THE PRINCIPLE OF PRECISE MEASUREMENT OF 2011). STANDING TREE OF CCD SMARTSTATION In order to sum up the advantages of the above method, this paper presents a nondestructive, rapid and accurate Systematic calibration of CCD SmartStation: When method for measuring height and volume of standing tree photogrammetric post-processing is carried out, precisely by using a CCD SmartStation. In the method, the exterior obtaining the exterior elements of the photograph directly elements are obtained by the goniometry and ranging meas- affects the accuracy of the measurement results. There are urement functions of the CCD SmartStation. The mode of mainly two kinds of systematic errors in the CCD single-photo photography and multi-photo correction and SmartStation systems, which are, respectively, optical dis- merging are adopted to obtain the tree height and volume tortion error of CCD lens and offset error between CCD lens factor of the standing tree by the principle of close-range center and total station center space position. In order to photogrammetry. The method has the advantage, which is improve the measurement accuracy, two systematic errors cheaper than the 3D laser scanner, and has a simple opera- need to be eliminated or reduced (Liu 2016, Feng 2015). tion. Compared with the traditional method, the method In this paper, DLT linear transformation method is used reduces the working time and the workload in the field. In to calibrate the optical distortion of CCD lens. Through the addition, the method can be operated by a single person principle of space resection of the single photograph, by without additional manual assistance, which achieves the using the ground control point and the corresponding pixel true sense of the non-contact measurement. Table 1 com- coordinates, iteratively solve the CCD extra ranging ele- Table 1: Comparison and analysis table of measurement method of a variety of timber volume. Measurement methods of Instrument prices and labour costs Work efficiency standing timber volume Method of 3D laser scanners Instrument prices are high (60~150 million yuan), Field workload is large; equipment is heavy and at least two people are needed to operate. not easy to transport; internal work is complex, and it requires professional software; measure- ment of a tree needs about 20 minutes in average, precision is high. Measuring method of monocular Instrument prices are low (0.1~0.8 million yuan), Field workload is small, and the equipment iseasy CCD digital camera two people are needed to operate. to carry. Office workload is moderate. The aver age time for measuring one tree is about 5 min utes, and the measurement accuracy is moderate. Method of electronic theodolite Instrument prices are low (0.3~0.8 million yuan), Field workload is large; human works are needed two people are needed to operate in cooperation for the auxiliary measure of the diameter of the chest, it is not suitable for continuous operations; internal work is tedious, people should distin guish and organize data string; measurement of a tree is about 15 minutes in average, accuracy is high. Method of TotalStation Instrument prices are medium (30~80 thousand Field workload is large. It requires the continu yuan), one person is needed to operate. ous work of the human eye and makes people tired easily. It is not suitable for continuous op eration; office work is moderate; measurement of a tree is about 12 minutes in average, accuracy is high. Method of CCD SmartStation Instrument prices are medium (30~80 thousand Field work is small. It doesn’t need the assistance yuan), one person is needed to operate. of other personnel, and operation is continuous; office workload is moderate; the measurement of a tree is about 5 minutes in average, accuracy is high. Vol. 17, No. 4, 2018 Nature Environment and Pollution Technology METHOD OF MEASURING TREE HEIGHT AND VOLUME BASED ON CCD SMART STATION 1307 the distance ZM from the projection center S to the center O of the tree, the height Hi of standing timber at any height and the diameter Di at the corresponding height. d tan Z= d 2 M ...(2) Fig.1: Relations diagram of observational distance and 1 tan angle of CCD SmartStation. 2 Z ments at the moment of shooting, make the simultaneous M RL Di X L u i u i ...(3) solution of the coordinate with position and attitude of the fcos vi sin instantaneous total station. The translation and rotation off- ZM L sets relative to the total station can be obtained.
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