Combining MLS & ALS Point Cloud Data
Bochove, D.P. van
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LiDaR point clouds can serve a wide range of applications. Generally speaking, point clouds can be obtained in two ways: Mobile Laser Scanning (MLS) or Airborne Laser Scanning (ALS). However, for certain applications using one of these two techniques is not sufficient. For some applications, the resolution of ALS point clouds is not sufficient. A disadvantage of MLS is that its positioning accuracy decreases significantly in urban areas, because the GPS signal is blocked by buildings. Apart from that, ALS provides little information on building façades, while MLS provides little information on roof tops. Therefore, the combination of ALS and MLS data offers interesting opportunities for new applications and the improvement of existing applications. In order to combine the two data sources, three operations have to be undertaken. The first step is to align the two point clouds. This process is also called registration. However, little is known about which of the known registration methods best suits the practical needs and applications of an organisation. The second operation is to integrate the two point clouds. Undoubtedly overlap of points will occur. It is important to decide which points are then removed, and which point cloud is regarded as ground truth. The third step is to make the data available in an accessible way. The municipality of Rotterdam, especially the department of Basic Information, that manages the municipality’s geographic information, is interested in point clouds developments and have an ALS point cloud of the city obtained every two years. They have also done two MLS pilots. This research focuses on finding out which point cloud combination methods suit the applications of the municipality the best. Two groups of point cloud users are identified: advanced users and basic users. These two groups are involved in a wide range of applications of point cloud data. Advanced users actively use point cloud data themselves and greatly benefit from the added value of a combined ALS-MLS point cloud. Advanced users would like to have full control over their point cloud data. On the other hand, basic users would benefit more if the data was made available to them in a more simplified form. This research proves that a combination of Airborne Laser Scanning and Mobile Laser Scanning data is of great added value.