A method of localizing transportable apparatus (200) within an environment includes receiving (402) data obtained from a first ranging sensor device (202) that is configured to collect information relating to a 2D representation of an environment (301) through which the transportable device is moving. Further data is received (404), that data being obtained from a second ranging sensor device (204) of the transportable apparatus configured to collect information relating to at least a surface (218) over which the transportable apparatus is moving. The ranging sensor device data is used (406) to estimate linear and rotational velocities of the transportable apparatus and the estimates are used (408) to generate a new 3D point cloud (212) of the environment. The method seeks to match (412) the new 3D point cloud with, or within, existing 3D point cloud (216) in order to localize the transportable apparatus with respect to the existing point cloud.