于DEM光照晕渲模拟的梯田自动提取方法

梯田作为黄土高原最为典型的人工地貌之一,有重要的农业生产和水土保持价值。传统的梯田自动提取仅限于梯田所在区域的范围划定,未能对梯田田坎线实现有效的自动化提取。鉴于此,本文提出了一种基于光照晕渲模拟的梯田快速提取方法。首先,对无人机航测生成的1 m分辨率的数字高程模型（DEM）进行4个方向的光照晕渲模拟,并相加取平均值;然后,通过适当的阈值对均值图像进行二值化,并掩膜掉沟谷等非梯田区域;最后,基于二值化图像自动矢量化得到梯田田坎线,并通过适当的长度阈值进行碎线过滤提高提取精度。本文以陕西省长武县王东沟流域为实验样区进行了实验,结果表明,该方法提取结果的准确率为89.09%,具有较好的提取精度。此外,对该方法涉及到的参数进行了讨论,表明光照模拟的方向角采用2个正交的对称方向对、高度角采用田坎坡度的反正切值、二值化阈值采用t=180-σ的经验公式,可以满足黄土高原的梯田自动快速提取。

An Automatic Retrieval Method for Artificial Terrace Based on Illumination Model of DEM Shading

As one of the most typical artificial landforms in loess plateau of China, artificial terraces have important value in agricultural production as well as soil and water conservation. The previous studies on terrace automatic extraction only focused on their boundaries and failed to achieve effective and automatic extraction of their ridge lines. In this study, a quick extraction method of terraces based on illumination and shading simulation of DEM is proposed. Firstly, illumination and shading simulation in four-direction is carried out using 1 m digital elevation model (DEM) generated by Unmanned Aerial Vehicle (UAV) technology and average value of four simulations was calculated. Secondly, the image of the mean value is binarized into a logistic image using a proper threshold. Also, valley and other non-terraced areas were masked off. Finally, terrace ridge lines were obtained by automatic vectorization of the logistic image. Some broken lines were filtered by a proper length threshold to improve the extraction precision. Taken Wangdonggou watershed, Changwu County, Shaanxi Province as the study area, the experiment results showed that this method had a preferable extraction accuracy of 89.09%. Furthermore, the parameters involved in this method were also discussed. The results showed that if we take two orthogonal symmetric direction angles as the direction angles, arctangent value of the slope of terrace ridges as the altitude angle, an empirical formula (t=180-σ) was used to calculate the threshold value of the logistic image, the quick automatic extraction of artificial terraces of loess plateau can be achieved.