In Metashape Professional edition both structured terrestrial laser scans and unstructured aerial laser scans can be imported using Import Point Cloud (select File > Import > Import Point Cloud) command. All point attributes including structured information are now preserved while importing. 


In this article the following topics are discussed:


Import trajectory

For terrestrial laser scans of the Lidar Backpack type, which record the trajectory file, it is important to first import the trajectory file before importing laser scans.


The following formats are supported for the trajectory import:  Character-separated values (*.txt, *.csv, *.trjt, *.xyz), SBET (*.out, *.sbet), SOL (*.sol), TerraScan (*.trj).


1. Select File > Import > Import Trajectory... command to import trajectory. 


2. Select the file with the trajectory. For character-separated values formats specify the following parameters: Columns (X, Y, Z, GPS Time), Delimiter (Tab, Comma, Semicolon, Space or other) and Skip rows in the Import Trajectory dialog window. For other formats, the data will be loaded automatically.


3. Click OK button.


The trajectory will be displayed in the Model view and new layer with the trajectory will also appear in the Workspace pane.



Import terrestrial laser scans

To import laser scans data into Metashape project its is required to import the point cloud via File > Import > Import Point Cloud... and then specify that this point cloud to be used as laser scans data. 


It is important to enable the Use as laser scans option.


You can add several point clouds at the same time. Select all point clouds from the folder with laser scans data that you want to import. In case several point clouds were selected, the parameters will be applied to all point clouds that you want to import.


In the Import Point Cloud dialog window specify parameters for import:



Parameters: 


  • Coordinate System: it is important to specify the coordinate system in which the laser scans were received. 
  • Coordinate Precision: you can specify a custom value for coordinate precision enable Custom (m) option and specify the value. Or use Default option, then Metashape calculate coordinate precision automatically. The value will correspond to the average precision value for all points from the point cloud.
  • Use as laser scans - enable option to import point cloud as a laser scan.
  • Load images - the option is available for laser scans with built-in panoramas. If the laser scans have panoramas stored, you can enable this option and then they will be uploaded to the project. If this option is unavailable or disabled, Metashape will automatically create panoramas using information from the point cloud.
  • Scanner position - to determine the normal of a point in a point cloud, Metashape approximates the local surface of the model with a plane. If the point cloud was obtained in an unstructured form, then Unknown option should be selected in the Scanner Position field. If the point cloud was recorded in a structured form, then the Origin parameter should be selected. If point cloud saves a trajectory file, then use - Trajectory parameter value.
IMPORTANT: if you imported a trajectory file in the previous step, then specify Scanner position - Trajectory.

  • Normal estimation neighbors  - in order to determine the normal of a point in a point cloud, Metashape approximates the local surface of the model with a plane. The direction of the plane is determined by the nearby neighbors of a given point. The number of nearby points to consider is determined by Normal estimation neighbors parameter. If the cloud is very noisy, 28 default neighbors may not be enough to confidently determine the normals. For such point clouds, it is worth increasing the Normal estimation neighbors value to 100. Increasing the number of neighbors will slow down the calculation, smooth out the normals at the corners, but will help to avoid noise. In some cases, increasing the number of neighbors can help avoiding large inverted plots.

  • Replace default point cloud - default point cloud will be replaced in the project if this option is enabled.

  • Point Attributes - depending on the information recorded in the laser scanning data, it is possible to choose which attributes to upload to the project.


The imported laser scans data is displayed as point clouds in the Workspace pane and in the Model view:




The point cloud and spherical panoramas with depth maps information (captured by the laser scanner) are also accessible on the Workspace pane:



For display only one point clod in the Model view select Set Active command from the laser scan context menu:



Depending on the information recorded in the laser scan data, the cloud can be displayed as various modes: Solid View, Colors View, Classes View, Intensity View, Elevation View, Return View, Scan Angle View, Source ID View, Confidence View. 


If you imported a point cloud without the Use as laser scans option enabled. then after importing, you can make a cloud with a laser scan. For this select all laser scans on the Workspace pane and choose Use as Laser Scan from the Point Clouds context menu:




Point cloud Bounding box

In the Model view there are 2 Regions visible around the point cloud. The red color indicates the Point cloud Bounding box. The green color indicates general bounding box for this chunk:


To disable bounding box for chunk: Select Model > Show/Hide Items > Show Region.

To disable bounding box for point cloud: Left-click on the Workspace pane (for example, click on the name of the chunk) and the red bounding box will not be visible in the Model view. If you double-click on point cloud, it will appear again:





In Metashape available to change the color for bounding boxes. Select Tools > Preferences... > Appearance tab:



Show laser scans position

To display the position of the scanner during shooting,  you need to enable Show Laser Scans >  Show Laser Scan Positions button on the Toolbar:




Alignment of laser scans between each other

Alignment for terrestrial laser scans can be performed in Metashape. To clarify the external orientation of the laser scans and align them relative to each other, before alignment, you need to disable the Lock transform option in the context menu for all laser scans:


If Lock Transform opiton is not disabled, the laser scans will not change their position after alignment, only tie points will be found, which can then be used to align the images to the laser scans.

Select Workflow > Align Laser Scans... command. In the Align Laser Scans dialog window specify the preferable parameters:



  • Accuracy - at High accuracy setting the software works with the original distance between points, Medium setting causes downscaling by factor of 4, at Low accuracy source files are downscaled by factor of 16, and Lowest value means further downscaling by 4 times more. Highest accuracy setting upscales the distance between points by factor of 4.
  • Reset current alignment - if this option is checked, all the key, and matching points will be discarded and the alignment procedure will be started from the very beginning. Uncheck this option to subalign some extra laser scans added to the chunk with already aligned set of laser scans. 


WARNING! If the laser scans were imported into a project with aligned images, then when using Reset current alignment option in the Align Laser Scans dialog box alignment will also be reset for images.


  • Key point limit - the number indicates upper limit of feature points on every laser scans to be taken into account during current processing stage. Using zero value allows Metashape to find as many key points as possible, but it may result in a big number of less reliable points. 
  • Vertical axis - set the vertical axis (X, Y or Z) of rotation of the laser scan.




Groups of laser scans

If you want to keep the alignment for a group of laser scans (they were previously aligned in a third-party program or taken on the same day), then the laser scans can be grouped. 


New Laser Scan Group

Select all the laser scans on the Workspace pane and select Move Laser Scans > New Laser Scan Group command from the laser scan context menu. Laser scans are grouped together. the group will be displayed in the Workspace pane:


Fixed Laser Scan Group

To save the positions of the laser scans relative to each other in this group, the group must be Fixed. Then the positions of the laser scans inside the group will remain unchanged, and the entire group will "move" when aligned.


Select Set Group Type > Fixed command in the group context menu on the Workspace pane: 



After you fixed the group, the group will have a common Lock transform parameter which works the same way as for laser scans:

  • If Lock Transform is enabled for a fixed group, then the external orientation of this group will remain unchanged and will be used as a reference. 
  • If Lock Transform is disabled, the external orientation for the group will be clarified and the group can change its position, but the laser scans inside the group will retain their position.


Processing terrestrial laser scans and images

Add images to the project with laser scans.  


If you want the laser scans to retain their position after alignment then don't disable the Lock Transform option neither the laser scans nor the group of laser scans if they are in the project.
 
If the laser scans can change their position and their coordinates are not accurately measured, it is important to disable the Lock Transform option for ALL laser scans and ALL group of laser scans before alignment.



Images and laser scans in the same coordinate system

Select Workflow > Add Photos... or Add Folder... command. Images will be added to the project. The images will be added to the project.


Select Workflow > Align Photos... to align images with laser scans: 



The result of the combined alignment of the laser scans and images will be displayed in the Model view:




Images and laser scans in different coordinate systems (use image coordinates as a reference)

If the data is received in different coordinate systems (terrestrial laser scan in local coordinate system and images in geodetic coordinate system). Before aligment, we recommend disabling the checkboxes for images on the Reference pane and disable the Lock transform option for laser scans.



Make sure that a coordinate system is set for the scan that matches the coordinate system for laser scans. Click Settings button on the Reference pane (in our example, the laser scans were imported in the local coordinate system, so we also set the local coordinate system for the chunk):



Then performing joint alignment of terrestrial laser scan and photos. Select Workflow > Align Photos... to align images with laser scans: 



After alignment, you can georeference the data using the coordinates of the images. Enable checkboxes for the images on the Reference pane and click Update button. 



After that, you can enable the Lock Transform option for laser scans. The laser scans will be georeferenced and the coordinates will be saved after export.