Method and apparatus for localizing transportable apparatus (100) within an environment (120) includes obtaining (202) point cloud data (114) representing a 3D point cloud with appearance information of at least part of the environment. The method further obtains (204) first frame data (110) representing an image produced by a sensor (102) onboard transportable apparatus at a first time and location within the environment and second frame data (110) representing an image produced by the sensor at a second time and location within the environment. The method harmonizes (206) information about the first frame data, the second frame data and an overlapping subset of the point cloud data in order to determine a location within the point cloud data where at least one of the first frame and the second frame was produced, thereby localizing (208) the transportable apparatus within the environment.