Enric Celaya Jose-Luis Albarral Pablo Jiménez Carme Torras Visually-Guided Robot Navigation: From Artificial to Natural Landmarks. 287-296 2007 FSR http://dx.doi.org/10.1007/978-3-540-75404-6_27 conf/fsr/2007 db/conf/fsr/fsr2007.html#CelayaAJT07