Evaluation of object surface edge profiles detected with a 2-D laser scanning sensor

Authors: YAN, TINGTING - Nanjing Agricultural University; WANG, XIAOCHAN - Nanjing Agricultural University; Zhu, Heping; LING, PETER - The Ohio State University

Submitted to: Sensors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2019
Publication Date: 5/8/2019
Citation: Yan, T., Wang, X., Zhu, H., Ling, P. 2019. Evaluation of object surface edge profiles detected with a 2-D laser scanning sensor. Sensors. 18(11):1-17. https://doi.org/10.3390/s18114060.
DOI: https://doi.org/10.3390/s18114060

Interpretive Summary: Development of precision variable-rate spray technology is needed to improve pesticide, fertilizer and irrigation application efficiencies for greenhouse crop production. An accurate sensor is a critical component for the new spray system development. With evidence of the dimension measurement accuracy of the laser sensor in our previous research, the goal of this research was to evaluate the edge profile detection accuracy of an indoor-use 270° radial range laser scanning sensor and a sophisticated algorithm before their integration to the greenhouse variable-rate spray system. Evaluations included: using the laser sensor and the algorithm to measure complex-shaped objects at different horizontal distances, sensor speeds and detection heights; analyzing number of the laser data points on the objects and the detection resolution of the laser sensor; reconstructing the pseudo-color images mapping the 3-dimensional object surfaces and detecting the edge profiles of the paired images from the laser sensor and the digital camera. The laser scanning sensor and the algorithm were capable of detecting surface profiles of the complex-shaped objects under greenhouse conditions. This research provided baselines for future integration of the laser sensor and the control system to the variable-rate sprayers to automatically control the spray outputs based on plant structures and travel speeds in real time for greenhouse applications.

Technical Abstract: Canopy edge profile detection is a critical component of plant recognition in variable-rate spray control systems. The accuracy of a high-speed 270° radial laser sensor was evaluated in detecting the surface edge profiles of six complex-shaped objects. These objects were toy balls with a pink smooth surface, light brown rectangular cardboard boxes, black and red texture surfaced basketballs, white smooth cylinders, and two different sized artificial plants. Evaluations included reconstructed three-dimensional (3-D) images for the object surfaces with the data acquired from the laser sensor at four different detection heights (0.25, 0.50, 0.75 and 1.00 m) above each object, five sensor travel speeds (1.6, 2.4, 3.2, 4.0 and 4.8 km h-1), and 8 to 15 horizontal distances to the sensor ranging from 0 to 3.5 m. Edge profiles of the six objects detected with the laser sensor were compared with images taken with a digital camera. The edge similarity score (ESS) was significantly affected by the horizontal distances of the objects, and the influence became weaker when the objects were placed closer to each other. The detection heights, travel speeds also influenced the ESS slightly. The overall average ESS ranged from 0.38 to 0.95 for all the objects under all the test conditions, thereby, providing a baseline information for integration of the laser sensor into future development of greenhouse variable-rate spray systems to improve pesticide, irrigation and nutrition application efficiencies through watering booms.