Georeferencing

PointCab FARO Scene Apps

In many scan projects, registration is realized in a local system. In Scene, a Cloud2Cloud or target based registration can be performed. In this process, a reference scan is used as origin. Subsequent georeferencing via known geodetic points in a global coordinate system is difficult.

Our Georeferencing Module as part of PointCab Scene apps georeferencing can be realized without much effort.

The registration of scan positions to each other remains unaffected, that means the internal registration accuracy of the scans to each other will not be modified. The allocation of spheres, targets or points in the scans to geodetic points is accomplished fully automatically; afterwards, it is consistently applied in the FARO Scene project by renaming. The cluster structure is completely retained in Scene.

Tutorialchapter

Georeferencing

Example

1. Open an existing FARO Scene project. Make sure that the registration of all scans has been accomplished.

2. Prepare the coordinate file of the geodetic points. In Scene, the coordinates must not have more than 4 pre-decimal positions. For example, you use Gauss-Krüger coordinates ( 3492100.753 5670106.768 600.000 ), subtract 3490000 and 5670000 from the second and the third column each time. Negative values in terms of reduction are permitted.

SceneApp_GeoRef_Cor

Coordinate file with ending .cor

Import a coordinate file with geodetic points via Drag&Drop into the Scene project. In Scene, a new folder “References” is created. It’s unimportant if you add the coordinate file to the project layer or cluster layer.

3. Open the scan views in which the geodetic points ae visible. If you have positioned checkerboard targets or reference spheres over the geodetic points, you measure them by means of the respective Scene tools. Otherwise, you measure the points by means of Scene’s point tool. You have to measure at least 3 points to be able to realize georeferencing.

SceneApp_GeoRef_Measure

4. Start PointCab Scene app by clicking on the PointCab logo in Scene menu. Open the view for “georeferencing”. Select “Update” to import the registration from Scene. In the feature list (targets, spheres and points), you see the coordinates measured in step 3 with their temporary names. The list of geodetic points contains the coordinates with the name from the coordinate file.

5. If you have used checkerboard targets or reference spheres, you can indicate a respective vertical deviation in the list of geodetic points. For this purpose, please double-click on the value. After a right mouse click, a menu opens and you can assign this value to all geodetic points.

SceneApp_GeoRef_Offset

6. Set the a priori accuracy of the different observations in the statistic model. If possible, you should set it according to the scan accuracy. The key factor is the relation of accuracies. Please notice that points generally feature considerably poorer accuracies than checkerboard targets and spheres. If geodetic points have been captured via GPS, you can assume an accuracy of 30mm, for example.

The value of the maximum difference is the maximum deviation for the assignment of a feature to a geodetic point. The value of overlapping indicates what percentage of geodetic points has been measured as features. This value significantly affects the calculating time for search. A value of 0% searches all kinds of assignments (brute-force).

Afterwards, you click on “Find constellation”. In the feature list, the names are changed accordingly via the detected assignment.

7. Sort the list regarding the columns of residuals by clicking on the respective header. In the list of features and geodetic points, all assigned points are highlighted in blue and the residuals are updated according to the calculated equalization. Features with large residuals should be checked and removed from the Scene project if necessary. Start with step 4 again.

The equalization defines the estimated variance factor ?0 allowing you to check the a priori accuracy expectations (about 1.0).

8. If you are satisfied with the equalization result, click on “Apply to workspace”. The new registration information is transferred to Scene. The cluster structure is retained and the Scan Managers are blocked automatically. Save the Scene project afterwards.

SceneApp_GeoRef_Result

Installation / deinstallation / update

The PointCab Scene apps contain all PointCab functions in a single plug-in for use with Scene and can be used according to your requirements.

Installation

By entering your data during the download, the download links for our products are automatically sent by mail. The PointCab Scene apps are compiled in a single ZIP file. Please unzip the ZIP file.

By double-clicking on the file PointCabSceneApp-v1.1.fpp, Scene starts automatically and installs the app. If you have got a dongle license from us, please install the file vcredist_x86.exe, too. You need administration rights for both steps.

thumbnail-plugin-faro

If the app is not available at the start of FARO Scene, please select Tools > Apps and activate PointCab Scene Apps.

SceneAppInstall

Deinstallation

Start Scene and deactivate the PointCab Scene apps in Tools > Apps. Close Scene and restart Scene now. Deinstall the PointCab Scene apps in Tools > Apps.

Update

Process the deinstallation first and use the new update for installation.