Point to point registration
Menu: File / Registration / Point to Point
This tool will move a given point cloud to match a reference point cloud. By selecting at least 3 corresponding points within both files, the algorithm calculates and processes the translation and rotation needed to move the second file accordingly. The adjustment is made using the least squares method.
To begin, the reference file and the file to be moved must be chosen with the drop-down list. Next, you must click on the “Show” button to view both clouds individually: the reference file in the main window and the file to be moved in a secondary window. To begin the registration, corresponding points must be added with the “+” click on “Pick reference point” to select a point in the main window. The XYZ coordinates for the reference point will then appear in the table. Retrieve the same area in the secondary window, click on “Pick “to move” point” and select a point corresponding to the same element. Once this is done, XYZ coordinates will be added for the “to move” point. Both point clouds need to overlap at least in part and at least 3 corresponding are needed for this registration method to work, but it is recommended to have at least 7 points to better judge the residual error and uncheck unwanted points where the residual is too high. It’s also preferable to vary the position of control points: try to have corresponding points in different sectors and elevations. The “X” button will suppress concordant points while unchecking them only discards them from calculations.
Once the control points are acceptable, the “Validate” button will analyse the transformation and show the difference between the XYZ points, the standard deviation of the transformation and the values of the translation and rotation calculated. The results can then be analysed and points may be re-picked, deleted or new points may be added for better results. Once the results are satisfying, click on “Apply” for the transformation between both scans which allows the user to view what the results would look like by showing both scans together in the main window. The “Back” button will remove any changes applied and will undo the transformation, while the “Reindex and reopen” button regenerates the index of the point cloud, making the change permanent. Note that if you “Apply” the transformation and quit VisionLidar, the index will automatically be recreated – this operation is also completed following the opening of a project. The “Report” button will save the results of the transformation in .TXT format giving a report of all points picked with the standard deviation and transformation values applied.
The registration could be made with an external file or reference file. To do so, you must check the option “External file” and select the file to be used. In this case the file to “move” is moved according to the external file.
When an external file is used, clicking on the “Reindex and reopen” button will create a new LAS file with the points at the new coordinates.