Registration in PointCab is a feature-based registration (target-based).
Laser scanner data from various manufacturers can be imported in PointCab at the same time.
Errors always occur in complex and large projects. Due to the clearly structured view, we provide a possibility to quickly and reliably identify wrong attributions, to remove them and thus to save a lot of time during registration. The workflow is our priority.
Moreover, our registration is able to directly georeference scan projects with reference points generated from total stations or GPS (We call them geodetic points.) in a common adjustment. If there are no geodetic points, any scan can be set as origin.
Example – FARO scan data in RAW format:
1. Required preferences
Select File > Settings and Registration tab. Here you can set preferences for a-priori accuracy of features (checkerboard targets, spheres, points) as well as your potential geodetic points (references). The relation of accuracies is decisive. Please respect that points generally provide significantly worse accuracies than checkerboard targets and spheres. If geodetic points are set via GPS, you can assume an accuracy of 30mm, for example.
Furthermore, you can determine if checkerboard targets and/or types of spheres shall be searched. These settings are automatically applied in each new project.
In the Sketch/Panorama tab, you deactivate the settings Colorized panorama to load scan views as reflectivity image more quickly later.
2. Create a project and import scans
Start a new PointCab project by selecting New > Advanced Importer. Enter a project name and save the project at a place of your choice. The Advanced Importer opens automatically.
Open your folder with FARO scans in RAW format using Windows Explorer or a comparable file browser. Select all scan folders together and drag and drop them to the free area in the Advanced Importer.
Select “No” for the question if the scans are already registered.
Now, all imported scans are listed automatically. As may be the case, add more scans in the same way.
Then, start the import by selecting Start. The import may take some time depending on the number of scans, data type, scan volume as well as computer resources.
Note: In case of FARO scans, colorization is realized automatically. If your computer is equipped with enough CPU cores and memory, several scans are imported at the same time. We recommend a SSD hard drive as system hard drive for quick import.
3. Registration Editor
After import, the Registration Editor opens automatically; the Advanced Importer is closed.
Make sure that Job List and Job Editor are displayed on the right (main toolbar or menu Views …)
The Registration Editor consists of 3 sections. The upper section incldes a dual view of two scans and allows to easily select corresponding points. Scans can be shifted manually for left or right side in the list box.
If you don’t need corresponding points, you can minimize or totally hide the right side by clicking and dragging into the intermediate area between both views. The dual view includes two hidden lists “Scans” and “Checkerboards & Spheres …” which can be made visible by clicking on the triangle.
The Scan List includes all available scans; the Feature List contains all available checkerboard targets, spheres etc. (currently empty).
The Job List shows a selected job “Registration“.
The Job Editor contains settings for registration. If not, simply click once on the job “Registration” in the Job List for selection. Now, you can individually adjust the settings for accuracies of features and feature search for this project.
If you have used external geodetic points in your project and if you want to import them, right-click into the Feature List and select “Load Coordinate File” in the context menu. The corresponding file formats are displayed; you can import your coordinate file that will be displayed in the list.
Note: You can sort the list corresponding to the column entries by clicking into the header.
4. Automatic feature detection
Start the registration job in the Job List. You will receive a message that some scans don’t have enough features and that they can be searched automatically. Confirm with “Yes”. A job for feature search is created for each scan in the Job List and automatically started.
The Scan List contains the column “Features” that shows the number of features in each scan. If only two or less features are found, the entry is red. If three or four features are found, is yellow, otherwise green.
When the search in all scans is realized, you can open a scan in the upper view and set it using the tools “sphere” or “checkerboard”. You save a lot of time since you can continue working simultaneously. For large projects, we recommend to check all scans visually and to remeasure features manually if needed.
You can open a scan in the scan list by right-clicking in the appearing context menu. In the context menu, you can activate / deactivate or set a scan as origin (as long as no geodetic points are used).
After the search process is finished, make sure that at least 3 features are found in each scan.
5. Search constellations automatically
Start the registration job in the Job List again. As the case may be, PointCab displays the same message if a scan doesn’t contain at least 3 features. Otherwise, a constellation detection is performed and attributions between the scans are searched.
If you have not set any geodetic points and any scan as origin, the first scan is automatically set as origin.
As a result of the search, the features are automatically renamed. If constellations can be found for all scans, a positive feedback appears and figure 0 appears in the column “group” for all scans. Otherwise, single scans or entire groups of scans could each exist in an own group. That means the groups could not be connected.
Check the scans regarding the features that should connect the groups, remeasure the missing features and restart the registration job. Perform this process as long as all scans are connected.
Note: In some cases, features have a weak configuration (e.g. all features are in line). By activating the option “Weak configurations” in the Job Editor, these features are used, too. If scans were not scanned vertically, deactivate the option “Assume leveling”. By increasing the search factor, more ambiguous attributions can be found – but this makes wrong attributions more probable.
6. Optimize registration
Now, all scans are preregistered, highlighted in blue in the scan list and orientation data of scans exists.
In the 3D view, which can be opened in the main toolbar, you can see the scan positions as well as geodetic points if available.
In the feature list, you see the initial residuals for each feature, that is the deviation of each feature from the average value of all three-dimensional coordinates of the features. The color shows how large the residuals are in relation to their a-priori accuracy. Red residuals show big deviations. Check them and delete the corresponding features if needed, and start again with step 5.
Start the registration job again.
Now, PointCab performs a global optimization and tries to attribute more features. Scan positions are optimized and the residuals’ square sum is minimized (Least Square Adjustment).
After adjustment is finished, all scans are green (origin scan is magenta). Check the residuals again. If required, delete the corresponding features, deactivate the option “incremental” and start again with step 5.
7. Finish registration and generate report
If desired, you can rename the log file in the File tab in the Job Editor.
Restart the registration job to generate the report and to finish registration.
The registration editor is closed and three default views are created automatically.
If a PDF viewer is installed, please open the report by double-clicking on the registration job. There, you find detailed information about the processed registration including accuracy specifications, a visualization of the feature graph, a detailed list of residuals as well as an accuracy analysis regarding the relative accuracy between scans (see Quality Matrix).