中文摘要：

为定量研究照相法测量规则林地覆盖度中采样策略、相机非垂直拍摄等因素对覆盖度计算结果的影响，该文对河北怀来的，一片梨树林进行了实地测量，通过对测量数据的统计计算，利用植被结构生成软件Onyxtreeprofessional重建梨树林场景，采用基于物理的光线追踪算法模拟相机拍摄的照片，提出了规则林地覆盖度照相法测量的采样方案，并通过计算机模拟检验了采样方案。通过精确控制模拟相机的拍摄条件，进一步分析了非垂直拍摄对测量精度的影响。结果表明，相机的非竖直拍摄对覆盖度计算结果的精度有较大的影响，误差最大町达27．9％。该文提出的测量方案为规则林地的覆盖度实地测量提供了参考。

英文摘要：

Digital photography is now the most widely used method to obtain the vegetation cover in field measurements. It uses a digital camera to shoot the research area straight downward, classify the digital images into plants and soil, and calculate the percentages of the pixel numbers of plants. When measuring the vegetation cover of regular planted woodland with digital photography, the accuracy of the calculated vegetation cover is affected by following factors such as the sampling strategy and non-vertical shooting of digital camera. However, it is difficult to analyze these factors mentioned above quantitatively in situ measurement because there are lots of uncertain errors involved. In this study, we used the computer simulation method to evaluate these factors because in a computer simulated scene, we can strictly control all these uncertainties. We measured a regular planted pyrus orchard to get the structural data in Huailai （40.373°N, 115.723°E）, Heibei province. Through statistics of the measured structural data, a regular planted pyrus orchard scene was reconstructed with the plants structural generating software, onyx tree professional which is widely used in forest management, plants reconstruction, and remote sensing of plants. Then the physically based ray-tracing （PBRT） algorithm was used to simulate the illumination conditions of the reconstructed scene and a virtual camera was simulated to get the images taken by a digital camera. The virtual camera settings are just like the digital camera when we measure the vegetation cover in situ. By controlling the shooting conditions strictly within the computer model, we can obtain simulated images under different shooting conditions. The supervised classification method was used to classify the simulated images to obtain the vegetation cover values. Due to the obvious three different samples in the regular planted woodland, this study proposed an area-weighted sampling strategy to calculate the vegetation cover of regular planted woodland. The stra