用YOLOv8和可解释AI分析激光点云,提升树种分类准确率至96%。
Enhancing Tree Species Classification: Insights from YOLOv8 and Explainable AI Applied to TLS Point Cloud Projections
- 通过Finer-CAM生成热力图,定位模型关注的树冠与树干区域。
- 平均准确率达96%(标准差0.24%),树冠是主要判别依据。
- 揭示不同树种依赖特征差异,适合林业与生态研究者参考。
为提升深度学习模型在基于TLS三维点云的树种分类中的可解释性,本文提出新框架,系统分析来自类激活图(CAM)的显著性图。利用来自7种欧洲树种共2445棵树的TLS三维点云数据,采用交叉验证训练了五个YOLOv8模型,测试集平均准确率达96%(标准差0.24%)。结果表明,Finer-CAM能忠实识别区分目标树种的关键区域。对630张显著性图的分析显示,模型主要依赖对应树冠的图像区域进行分类;而在欧洲山毛榉、英国橡树、挪威云杉中尤为明显;而欧洲梣树、苏格兰松和道格拉斯冷杉则更依赖茎干区域。结果显示,二维侧视图中结构特征的可见性提升了模型的判别性能,体现YOLOv8对点云细节的有效利用。本研究为理解树种分类模型决策过程提供了初步路径,有助于识别数据集与模型局限,增强预测可信度。
原文摘要 · Abstract (English)
Aiming to advance research in the field of interpretability of deep learning models for tree species classification using TLS 3D point clouds we present insights in the classification abilities of YOLOv8 through a new framework which enables systematic analysis of saliency maps derived from CAM (Class Activation Mapping). To investigate the contribution of structural tree features to the classification decisions of the models, we link regions with high saliency derived from the application of Finer-CAM to segments of 2D side-view images that correspond to structural tree features. Using TLS 3D point clouds from 2445 trees across seven European tree species, we trained five YOLOv8 models with cross-validation, reaching a mean accuracy of 96% (SD = 0.24%) when applied to the test data. Our results demonstrate that Finer-CAM can be considered faithful in identifying discriminative regions that discriminate target tree species. This renders Finer-CAM suitable for enhancing the interpretability of the tree species classification models. Analysis of 630 saliency maps indicate that the models primarily rely on image regions associated with tree crowns for species classification. While this result is pronounced in Silver Birch, European Beech, English oak, and Norway Spruce, image regions associated with stems contribute more frequently to the differentiation of European ash, Scots pine, and Douglas-fir. We demonstrate that the visibility of detailed structural tree features in the 2D side-view images enhances the discriminative performances of the models, indicating YOLOv8`s abilities to leverage detailed point cloud representations. Our results represent a first step toward enhancing the understanding of the classification decision processes of tree species classification models, aiding in the identification of data set and model limitations, and building confidence in model predictions.
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