The first use of a photogrammetry drone to estimate population abundance and predict age structure of threatened Sumatran elephants oleh Dede Aulia Rahman, Riki Herliansyah, Beginer Subhan, Donal Hutasoit, Muhammad Ali Imron, Didik Bangkit Kurniawan, Teguh Sriyanto, Raden Danang Wijayanto, Muhammad Hilal Fikriansyah, Ahmad Faisal Siregar, Nyoto Santoso