Sains Malaysiana 50(11)(2021): 3193-3204

http://doi.org/10.17576/jsm-2021-5011-04

Extracting Crown Morphology with a Low-Cost Mobile LiDAR Scanning System in the Natural Environment

(Mengekstrak Morfologi Silara dengan Sistem Pengimbasan LiDAR Mudah Alih Kos Rendah pada Alam Sekitar Semula Jadi)

KAI WANG¹, JUN ZHOU²*, WENHAI ZHANG¹ & BAOHUA ZHANG¹

¹College of Engineering, Nanjing Agricultural University, Nanjing 210031, China

²Jiangsu Province Key Laboratory of Intelligent Agricultural Equipment, Nanjing 210031, China

Received: 16 August 2020/Accepted: 7 March 2021

ABSTRACT

To meet the demand for intelligent measurements of canopy morphological parameters, a mobile LiDAR scanning system with LiDAR and IMU as the main sensors was constructed. The system uses a LiDAR-IMU tight coupling odometry method to reconstruct a point cloud map of the area surveyed. After using the RANSAC algorithm to remove the map ground, the European clustering algorithm is used for point cloud segmentation. Finally, morphological parameters of the canopy, such as crown height, crown diameter, and crown volume, are extracted using statistical and voxel methods. To verify the algorithm, a total of 43 trees in multiple plots of the campus were tested and compared. The algorithm defined in this study was evaluated with manual measurements as reference, and the morphological parameters of the canopy obtained using the LOAM and LeGO-LOAM algorithms as the basic framework were compared. Experiments show that this method can be used to easily obtain the crown height, crown diameter, and crown volume of the area; the correlation coefficients of these parameters were 0.91, 0.87, and 0.83, respectively. Compared with the LOAM and LeGO-LOAM methods, they were increased by 0.004, 0.12, and 0.13 and 0.07, 0.15, and 0.04, respectively. The test results for this new system are positive and meet the requirements of horticulture and orchard measurements, indicating that it will have significant value as an application.

Keywords: Canopy measurement; mobile LiDAR scanning system; point cloud segmentation; tightly-coupled odometry

ABSTRAK

Bagi memenuhi permintaan untuk pengukuran parameter morfologi kanopi yang cerdas, sistem pengimbasan LiDAR mudah alih dengan LiDAR dan IMU sebagai sensor utama telah dibina. Sistem ini menggunakan kaedah odometri gandingan erat LiDAR-IMU untuk menyusun semula peta awan titik kawasan yang dikaji. Setelah menggunakan algoritma RANSAC untuk menghilangkan landasan peta, algoritma pengelompokan Eropah digunakan untuk segmentasi awan titik. Akhirnya, parameter morfologi kanopi, seperti tinggi silara, diameter silara dan isi padu silara, diekstrak menggunakan kaedah statistik dan voksel. Untuk mengesahkan algoritma, sebanyak 43 pokok di beberapa petak kampus diuji dan dibandingkan. Algoritma yang ditentukan dalam kajian ini dinilai dengan pengukuran manual sebagai rujukan dan parameter morfologi kanopi yang diperoleh menggunakan algoritma LOAM dan LeGO-LOAM sebagai kerangka asas dibandingkan. Uji kaji menunjukkan bahawa kaedah ini dapat digunakan untuk mendapatkan ketinggian silara, diameter silara dan isi padu silara dengan mudah; pekali korelasi parameter ini masing-masing 0.91, 0.87 dan 0.83. Berbanding dengan kaedah LOAM dan LeGO-LOAM, mereka masing-masing dinaikkan sebanyak 0.004, 0.12 dan 0.13 dan 0.07, 0.15 dan 0.04. Hasil ujian untuk sistem baru ini adalah positif dan memenuhi syarat pengukuran hortikultur dan kebun yang menunjukkan bahawa ia akan memiliki nilai yang signifikan sebagai aplikasi.

Kata kunci: Odometri gandingan erat; pengukuran kanopi; sistem pengimbasan LiDAR mudah alih; titik segmentasi awan

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*Corresponding author; email: zhoujun@njau.edu.cn