Inter-alia, a method is disclosed comprising: obtaining one or more first location estimates; obtaining one or more pieces of optical information; and/or obtaining one or more second location estimates; if one or more pieces of optical information are obtained: determining one or more second location estimates at least partially based on the one or more pieces of optical information; determining a matching information indicative of whether at least one first position of the one or more first location estimates relatively matches at least one second position of the one or more second location estimates; and determining one or more third location estimates.
It is further disclosed an according apparatus, computer program and system.