Georeference Point Cloud Scans

If your project includes a movable scan (a scan from a scan station set up on an unknown position) or movable station group (a registered station group that does not include scans from survey stations set up on known positions), you can use the Georeference Scans command to georeference it to survey points with known positions. One or more georeference point pairs can be selected to perform the transformation:

One point pair - The data will be translated (moved) only.
Two point pairs - The best transformation that keeps the Z axis unchanged will be used.
Three or more point pairs - The best transformation based on all point pairs will be used. If the scan or group was leveled, the resulting transformation will be constrained in the Z axis.

Note: You can also run this command from the Georeferencing tab in the Register Scanscommand pane as part of a comprehensive workflow that includes scan registration, refinement , and georeferencing. However, if you have previously registered and refined multiple point cloud scans into a single movable station group, or your project includes a single movable point cloud scan that is not part of a registered station group, you can quickly perform georeferencing of the station group or individual scan using the Georeference Scans command.

Note for Trimble Perspective users: Georeferencing of scans and control points performed in Trimble Perspective is not as accurate as it could be because the scans are ground-scaled while the control points are grid-scaled. When you georeference scans in TBC, the point cloud is scaled to grid to ensure the georeferencing is as accurate as possible. Therefore, if a message displays alerting you to excessive errors in the georeferencing performed in the field software, it is recommend that you perform georeferencing in TBC as described here.

Prerequisites:

See the Subscription Plans page. For a license matrix by command, see the License page in the TBC Community. Also see View and manage licensed features.
A movable scan or registered station group.

To georeference point cloud scans:

Select Georeference Scans in Point Clouds > Registration to display the Georeference Scans command pane.
In the Select drop-down list, select the movable scan or registered station group you want to georeference.
If you select a station group, the stations included in the group are displayed in the list beneath it.
If you are working with imported scan data that includes one or more control points and survey-quality, scanner-based laser observations of those points (for example, Trimble X7 scanner data collected with Trimble Perspective field software), the Generate Pairs button and Georeferencing automatically check box are enabled. Proceed with step 3. Otherwise, go directly to step 4.
Note: A Perspective user can select to link a laser observation to a control point in the field to enable georeferencing of the scan in Perspective and/or TBC. In this case, the paired observation and control point are assigned the same name. When the data is imported into TBC, this pairing is referred to as an "imported point pair".
If you are working with imported point pairs, do either of the following
- To display imported point pairs in the Define Transformation list, click the Generate Pairs button.
  For each imported point pair, the coordinate for the control point and the coordinate for the corresponding observation are displayed in editable fields. Residual values that would result from georeferencing are also displayed for your review before proceeding. If necessary, change the coordinate in any of the fields by entering or selecting a different coordinate. Or, click the Delete button to remove an imported point pair from the Define Transformation list so that it is not used for georeferencing.
  If applicable, proceed to step 4 to manually add additional point pairs to the list. Otherwise, go directly to step 6.
- To automatically perform georeferencing using imported point pairs with no additional input (that is, you do not need to edit coordinates or manually add additional point pairs to the list), check the Automatic check box. Then press F4 to compute the project.
  When you check the Automatic check box, the Backsight property displayed in the Properties pane for the imported scan observations changes from No to Yes. Just as total station backsight observations can be used to compute a total station resection, backsight scan observations are used to georeference a group of point cloud stations.
  Note: This option eliminates the need for subjective point selection, resulting in more consistent results.
To manually add point pairs to the Define Transformation list:
1. Click in the Point ID field, and then select in a graphic view or the Project Explorer the survey control point to which you want to georeference the scan. Or, type in the point ID.
2. Click in the Scan point field, and then select in a graphic view the observable feature in the scan you want to georeference to the selected survey control point.
  The nearest scan point will be selected.
Optionally, create additional point pairs to use for georeferencing.
After you enter a second point pair, residual values that would result from georeferencing are displayed for each point pair based on your selections.
Note that you can select to exclude any point pair from being used for georeferencing by unchecking its check box. Or, click its Delete button to remove it altogether.
When you are done selecting point pairs, click the Georeference button.
The georeferencing process completes and the project is automatically computed. Movable scans are transformed accordingly.
If necessary, repeat to georeference additional movable scans or station groups.
Note: Point clouds scans that were registered prior to or after import will scale correctly (the appropriate scale factor is applied) when they are georeferenced to a new location or the coordinate system specified for the project is changed.