3D LASER SCANNING PRINCIPLES
SCAN SHADDOW
3D laser scanners work on 'a line of site basis', which means a 'shadow' is created behind objects and no point cloud is created.
Because of this multiple scans are required to capture all surfaces. In the extreme case of an empty sqare room, only one scan would be required. However for a typical plant room over 30 scans can be required to capture all surface details. It should be noted that in practical terms it is impossible to capture every surface detail.
SCAN RESOLUTION
Scan resolution needs to be set according to the outputs required from the point cloud. Low resolution scans will be faster and for low detail are perfectly adequate. However if high detail is required { or objects are small } then a high resolution scan is required to capture all the detail. Individual scan times can vary between 5 and 60 minutes and this will obviously affect how many scans can be carried out in a day. Different regions can also be scanned at different resolutions during the same scanning project, depending on the point cloud requirements.
REGISTRATION AND COLOUR MAPPING
Multiple scans are registered automatically during post scanprocessing. The process locks all the individual scans together to produce the point cloud. The point cloud is also coloured using the high definition colour photographs taken during the scanning process. The colour map is registered to the point cloud by assigning an RGB colour value to each of the millions of scan points. This procduces a 3D photographic quality point cloud.
DATA WHICH CAN BE BUILT UPON
Although it is always better to scan an area with multiple scans in one go, it is not always possible. Factors may be restricted budgets, time constraints or personnel access restrictions. One benefit of point clouds is that they can be added to and enhanced at any time in the future. This means that rooms can be partialy scanned initially then { if required } the missing parts can be scanned and added at a later date. This also applies to resolution, enabling an existing low resolution scan to be enhanced with full or partial high resolution data.
