https://s6.picofile.com/file/8379688376/_Lecture_Notes_in_Computer_Science_4853_Sumit_Sen_auth_Frederico_Fonseca_M_Andrea_Rodríguez_Sergei_Levashkin_eds_GeoSpatial_Semantics_Second_International_Conference_GeoS_2007_Mexico_C.pdf.html