Pinheiro, Helena Saraiva Koenow, et al. “Elevation Models for Obtaining Terrain Attributes Used in Digital Soil Mapping”. Pesquisa Agropecuaria Brasileira, vol. 47, no. 9, Nov. 2012, pp. 1384-9, doi:10.1590/S1678-3921.pab2012.v47.11091.