@conference {, title = {3D Position Estimation of an UAV in Indoor Environments using an Ultrasonic Local}, booktitle = {International Conference on Indoor Positioning and Indoor Navigation (IPIN 2018)}, year = {2018}, month = {09/2018}, pages = {1-8}, publisher = {IPIN}, organization = {IPIN}, address = {Nantes Francia}, author = {Gualda, D and Ure{\~n}a, J. and M.C.Perez and R. Nieto} }