Surveyors have special needs for the registration of laser scanner data. Often, additional points measured with a total station or via GPS are introduced to stabilize the registration and perform georeferencing. Furthermore, the verifiability of the accuracy will be required, e.g. for public-sector clients. This can be achieved by our statistical analysis and a full PDF report. In complex and large projects, mistakes are unavoidable. Due to the clear overview, you can identify wrong feature associations quickly and reliably and, thus, you save a lot of time on the registration.
Geodetic Registration can be used to directly georeference Scene projects in a common adjustment using reference points from a total station or GPS system (we call them geodetic points). If no geodetic points are available, the first scan would be used as the origin of the coordinate system.
1. Open a Scene project. Make sure that each scan has been registered with targets, spheres and/or point attributions (features). Each scan needs at least 3 features to be registered. Start the PointCab Scene app by clicking on the PointCab logo in the FARO Scene menu.
2. Open the “Geodetic Registration” view. Press “Update workspace” to import the registration of the Scene project into the app. In the list of the scans, you see the number of features (targets, spheres and points) per scan. In case the number of features of a scan is less than 3, the scan can not be considered.
3. Press “Analyze” to get a first analysis of the registration system. In the list of the targets, spheres and points (features), the initial residuals will be displayed in different colors.
The color depends on the a priori accuracy of the different features.
Scroll through the list and identify possible mistakes in the attribution. You can correct the mistakes in the Scene project.
Click on the PointCab logo in the menu again to open the app window in the foreground. Repeat step 2 and 3 until the residuals are small and all attributions are correct.
4. Set the a priory accuracy of the observations in the statistical model. The values should be close to the real accuracy of the different observation types.
It’s more important that the ratio is correct since the different observations will be balanced in the adjustment. Please keep in mind that measured points usually are more inexact than targets or spheres. The accuracy of geodetic points measured via GPS is usually 30mm. You can deactivate the use of geodetic points. In this case, the first scan will be fixed as the origin of the coordinate system.
Click “Adjustment” to process the registration. The updates for the position and alignment are displayed in the list of scans. The computed residuals in the list of targets, spheres and points as well as the list of the geodetic points will be updated.
The adjustment computes the estimated variance factor ?0 allowing you to verify the assumptions of a priori accuracy (about ~ 1.0).
5. Click “Report” to get a PDF with a detailed overview of the adjustment results. If a PDF viewer is installed, the PDF opens automatically. The PDF file contains detailed information about the calculated registration with accuracies, a visualization of the feature connection graph, an overview of all observations with the residuals and the accuracy analysis as a measure of the relative quality between the scans (see quality matrix).
6. If the adjustment has been computed successfully and the expected accuracies are suitable, click “Apply to workspace”. The new registration will be assigned to the Scene project. The Scene cluster structure remains, all ScanManagers will be locked automatically. Save the Scene project afterwards.