An apparatus for a motor vehicle driver assistance system , the apparatus being operable to initialise and optimise a plurality of object clusters, each of the object clusters including at least one object track, wherein each object track includes a plurality of sequential measurements of the position of a respective object located in the vicinity of the motor vehicle, and each object track has a track length, the apparatus being configured to perform the following steps: a) assign the position measurements of the plurality of object tracks to a collection of object clusters, wherein each object cluster includes at least one position measurement from at least one of the object tracks, b) calculate a respective value of a first diagnostic for each object cluster in said collection; c) based on the values of the first diagnostic, identify a rogue object cluster; d) from the object tracks whose position measurements are assigned to the rogue object cluster, identify as a rogue object track the object track having the longest length; e) remove the sequence of position measurements corresponding to the rogue object track from all object clusters; f) reassign any remaining position measurements previously assigned to the rogue object cluster to other object clusters in the collection, and; g) remove the rogue object cluster from the collection, to thereby optimise the object clusters. each of the object clusters including at least one object track, wherein each object track includes a plurality of sequential measurements of the position of a respective object located in the vicinity of the motor vehicle, and each object track has a track length, the apparatus being configured to perform the following steps: a) assign the position measurements of the plurality of object tracks to a collection of object clusters, wherein each object cluster includes at least one position measurement from at least one of the object tracks, b) calculate a respective value of a first diagnostic for each object cluster in said collection; c) based on the values of the first diagnostic, identify a rogue object cluster; d) from the object tracks whose position measurements are assigned to the rogue object cluster, identify as a rogue object track the object track having the longest length; e) remove the sequence of position measurements corresponding to the rogue object track from all object clusters; f) reassign any remaining position measurements previously assigned to the rogue object cluster to other object clusters in the collection, and; g) remove the rogue object cluster from the collection, to thereby optimise the object clusters. a) assign the position measurements of the plurality of object tracks to a collection of object clusters, wherein each object cluster includes at least one position measurement from at least one of the object tracks, b) calculate a respective value of a first diagnostic for each object cluster in said collection; c) based on the values of the first diagnostic, identify a rogue object cluster; d) from the object tracks whose position measurements are assigned to the rogue object cluster, identify as a rogue object track the object track having the longest length; e) remove the sequence of position measurements corresponding to the rogue object track from all object clusters; f) reassign any remaining position measurements previously assigned to the rogue object cluster to other object clusters in the collection, and; g) remove the rogue object cluster from the collection, to thereby optimise the object clusters. <EOS>