Constrained Multi-Objective Optimization of Simulated Tree Pruning with Heterogeneous Criteria

Damjan Strnad,Štefan Kohek

doi:10.3390/app112210781

Abstract

Virtual pruning of simulated fruit tree models is a useful functionality provided by software tools for computer-aided horticultural education and research. It also enables algorithmic pruning optimization with respect to a set of quantitative objectives, which is important for analytical purposes and potential applications in automated pruning. However, the existing studies in pruning optimization focus on a single type of objective, such as light distribution within the crown. In this paper, we propose the use of heterogeneous objectives for discrete multi-objective optimization of simulated tree pruning. In particular, the average light intake, crown shape, and tree balance are used to observe the emergence of different pruning patterns in the non-dominated solution sets. We also propose the use of independent constraint objectives as a new mechanism to confine overfitting of solutions to individual pruning criteria. Finally, we perform the comparison of NSGA-II, SPEA2, and MOEA/D-EAM on this task. The results demonstrate that SPEA2 and MOEA/D-EAM, which use external solution archives, can produce better sets of non-dominated solutions than NSGA-II.

Highlights

Pruning is one of the most important horticultural intervention techniques with which the vegetative and reproductive growth of fruit trees can be balanced
We are interested in the relation of generated pruning solutions to three reference proposals, corresponding to non-pruning, non-selective pruning to cylindrical shape, and distance-based pruning, where the secondary branches are removed if their distance to the primary ones is below the threshold
Compare the performance of NSGA-II, SPEA2, and MOEA/D-EAM on this problem, which is important from the perspective of future framework development

Summary

Introduction

Pruning is one of the most important horticultural intervention techniques with which the vegetative and reproductive growth of fruit trees can be balanced. A number of software tools have emerged for computer-aided horticultural education [4,5,6,7]. They complement the field training by allowing the user to perform various actions on simulated tree models within a 3D virtual environment. The effects of such interactive tree manipulation on its growth are simulated to provide an informative feedback to the user. The use of software tools can be extended beyond education, since they allow analysis and comparison of various tree training techniques

Objectives

Methods

Results

Discussion

Conclusion