Combining UAV Imagery, Volunteered Geographic Information, and Field Survey Data to Improve Characterization of Rural Water Points in Malawi. - Marc van den Homberg; Arjen Crince; Jurg Wilbrink; Daniël Kersbergen; Gumbi Gumbi; Simon Tembo; Rob Lemmens (ISPRS Int. J. Geo Inf., 2020)