Yao, Lijian, et al. “Depth Recovery for Unstructured Farmland Road Image Using an Improved SIFT Algorithm”. International Journal of Agricultural and Biological Engineering, vol. 12, no. 4, Aug. 2019, pp. 141-7, https://www.ijabe.migration.pkpps06.publicknowledgeproject.org/index.php/ijabe/article/view/4821.