# An Image Processing Method for Measuring the Surface Area of Rapeseed Pods
## 1 Introduction
3-D measurement technology uses a computer vision method to reconstruct a 3-D model of the object [25]. It is necessary to use a laser scanning system to obtain the image and use image processing, vision technology, and point-cloud data processing technology [26] to perform in-depth mining and extract the features of the 3-D data of the measured object [27; 28] to realize the 3-D digitization of the relevant measurement indices of the measured object. 3-D technology has been widely used in recent years to measure the related terrestrial space position and size because it can restore the actual shape and characteristics of the measured object truly. The relevant measurement indicators [29], such as distance and object surface area and volume, can be directly calculated. There are many application examples of the 3-D measurement technology in measuring the surface area and volume of objects,  
Figure 1: Two dimensions of the surface area measurement of rapeseed pods. including the surface area and volume of fish [30], the surface area of coral [31], cranial volume [32], and the surface area of human feet [33] and female breasts [34]. In the field of agriculture, there are reports of the non-destructive measurement of the surface area and volume of sweet potato (_Ipomoea batatas_) [35] and storage roots [36] using an inexpensive 3-D scanner. Therefore, to our knowledge, a high-precision 3-D laser scanning system, which ensures the accuracy of measurement results, was used to measure the pod surface area for the first time. The results were compared and corrected with the measurement results of the image processing technology proposed in this experiment. The multi-pod measurement is a process of the batch measurement of multiple rapeseed pods to obtain the total area value. It is widely used and has more practical significance than measuring a single pod. The primary methods used for this measurement include accumulating a single pod area and fresh-weight measurement methods. The accumulation of the area of a single pod was used to measure the surface area of all the pods; then, the measured value that had accumulated was obtained. The method used to measure the single pod measurement described above is still required to measure a single pod. The accumulation measurement of a single pod area can be challenging because of the highly complex operations and the heavy workload involved. Therefore, this technique has been briefly discussed in the experimental methods section of a few studies, and some systematic studies have reported it. The fresh-weight method is based on the area and mass of a few samples determined by single pod measurement, i.e., scanning flattening. The approximate area of the sampled pods can be obtained by data transformation on the ratio of the mass of the sampled pods to the mass of the pods with a known area. Although such methods are simple and efficient, they produce considerable errors owing to the uneven texture of rapeseed pods [14]. In summary, single pod measurement is currently the mainstay for measuring rapeseed pod surface areas because most methods have difficulty being both \"highly accurate\" and \"highly efficient\". This study is a subproject of the \"Rapeseed Ideal Plant Type Breeding Project\" of the Hunan Branch of the National Oilseed Crops Improvement Center (Changsha, China). This study aimed to screen ideal rapeseed plant types with high grain yields using multiple pod areas of a single plant dimension as important indices. Based on the results obtained by our group and focusing on the measurement goal of \"highly accurate, highly efficient and large-scale\", we established a correction model using the measurement principle of oblique-cylinder side area calculus and the results with a high-precision 3-dimensional (3-D) laser scanner. We proposed a new method to determine the areas of rapeseed pod surfaces on image processing and to conduct precise and efficient measurements of multiple pod surface areas.