中文摘要：

为了提高农产品数值模拟的精度,需要为其提供精确的农产品几何模型。该研究以具有不规则几何特征的农产品芒果、香蕉和苹果为试验对象,利用核磁共振成像仪获取的断层切片图像,借助于计算机图形学技术和视觉化工具函数库Visualization Toolkit5.4（VTK）,实现了其几何模型的重构。结果表明,3种农产品几何模型的体积值与其真实值之间的误差均小于3%,与标准方法测得结果具有很好的一致性。该研究为农产品几何模型获取提供了一种新的方法,能为农产品数值模拟、有限元分析以及品质检测等提供直接的几何模型支持。

英文摘要：

Modeling and simulation of agricultural products during harvesting, storage, and transportation process are very important issues in agricultural postharvest engineering field. Considering transport phenomena principles involved in the model formulation, a geometry representing the real object is needed to be defined. However, since agricultural products are usually naturally irregular in shape, accurate acquisition of their geometric model becomes essential. In this research, the model reconstruction process which consists of magnetic resonance imaging, image processing and reconstruction method allows obtaining accurate geometric models even for agricultural products with very irregular shapes. Some typical agricultural products with irregular shapes, such as mango, banana and apple, were selected as the experimental samples to reconstruct their geometry models from magnetic resonance imaging data. All NMR data were acquired from a GE whole-body magnetic resonance imaging system with a static magnetic field of 3.0 Tesla. Samples were fixed on a plastic holder and then manually focused to obtain the images. MR images were generated using a fast spin echo sequence with effective echo time of 65 ms, repetition time of 1800 ms, slice thickness of 2 mm, and field of view of 512 512 pixels. In order to better acquire the irregular contour curves of each MR image, several image preprocessing steps implemented in MATLAB were applied to all original the MR images, the steps are as follows： （1） gray level transformation of the original gray level images; （2） median filtering for noise reduction and image quality enhancement; （3） segmentation through an adaptive threshold segmentation algorithm; （4） image filling and ensure each image only has a single contour curve. A procedure to obtain geometric models of irregular agricultural products was developed by the computer image graphics technology. The whole model reconstruction process was implemented in Visualization Toolkit 5.4. The contour curves approx