1. a Institute of Geodesy and Photogrammetry (IGP) , ETH Zurich (ETHZ) , Wolfgang‐Pauli‐Str. 15, 8093 Zurich, Switzerland
2. b Institute for Photogrammetry and Remote Sensing , Chinese Academy of Surveying and Mapping , 16 Beitaiping Road, Haidian District, Beijing 100039, PR China
3. c Swiss Federal Institute for Forest , Snow and Landscape Research (WSL) , Department of Landscape Inventories , 8903 Birmensdorf, Switzerland