Derik Schröter Thomas Weber Michael Beetz Bernd Radig Detection and Classification of Gateways for the Acquisition of Structured Robot Maps. 553-561 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3175&spage=553 2004 conf/dagm/2004 DAGM-Symposium db/conf/dagm/dagm2004.html#SchroterWBR04