How to align more Crane Camera projects from a construction site

What is a site alignment?

To make sure that all the datasets belonging to the same site are not shifted and to enable accurate measurements and comparisons, an alignment operation is required.

When a new dataset is added to the site and processed, there are two different methods that Pix4D uses for the alignment:

  • Sites with no GCPs use the Ortho-alignment, which aligns the Orthomosaic and DSM only (the Point Cloud is not touched).
  • Sites with GCPS use the AutoGCPs-alignment, which aligns the Orthomosaic, the DSM and the Point Cloud.

The sites using any of those two algorithms are called "aligned".

As a result, the new outputs will be adjusted to match the reference ones. The 3D textured mesh will not be impacted.

 
Note: The sites with GCPs where the AutoGCPs detection algorithm did not find at least 3 GCPs will also apply the Ortho-alignment method.

How to know if my site is marked as aligned?

 
Access: Aligned sites are available only for Crane Camera users.

The site alignment is triggered by Pix4D. Please contact the Crane Camera Support to get updates about the alignment status of your site.

How to ensure the alignment will work correctly?

With the Ortho-alignment

  • The whole site should be captured.
  • A minimum number of images per dataset will be defined by Pix4D for each of the sites based on initial analysis. That minimum number of images has to be reached for the algorithm to be successful and have the dataset marked as trusted for future alignment.
  • A certain percentage of images with respect to the trusted project is needed. By default, it is 80%. For example, if a project has 100 images, the next-day project should have at least 80 images for the Ortho-Alignment to work properly.

Both the minimum number of images and the percentage are defined by Pix4D.

 
Note: When the project does not have GCPs, the output coordinate system will be the default WGS84 projected in UTM.

With the AutoGCPs-alignment

  • The whole site should be captured.
  • The site should have at least 3 GCPs, although it is recommended to have more than three.
  • The GCPs should meet the requirements to be recognized by the AutoGCPs detection algorithm.
 
Tip: Download the Crane Camera GCP Targets installation user guide to know more about target requirements, placement, and best practices.
 
Important: If the algorithm cannot find at least 3 GCPs, the Ortho-alignment algorithm will be applied. The Ortho-alignment algorithm can be less precise and will not align the 3D scene.
 
Important: If the GCPs are moved or changed, inform the Crane Camera Support, sending the updated GCP file with the new coordinates.
 
Note: When having GCPs, the output coordinate system will be the one of the GCPs. If none of the GCPs are detected, the coordinate system will be the default WGS84 projected in UTM.

What is displayed on the Pix4Dcloud Advanced user interface?

Different labels and messages are displayed in the user interface according to the quality of the alignment of the site.

Sites with GCPs

 

GCPs aligned dataset

If the AutoGCPs algorithm has been able to find at least 3 GCPs, the AutoGCPs-alignment will be run.

  • The user interface will the label GCPs_aligned_dataset.jpg in the 2D and 3D views.
  • The output coordinate system will be the same as the GCPs' one.
  • The Orthomosaic, the DSM and the Point Cloud will be perfectly aligned and georeferenced.

2D aligned dataset

If less than 3 GCPs were found by the AutoGCPs algorithm, the Ortho-alignment will be run.

  • The user interface will display the label  2D_aligned_dataset.jpg.
  • The output coordinate system will be the same as the GCPs' one.
  • The Orthomosaic and the DSM will be aligned.
 
Warning: Under these conditions:
  • The point Cloud is not aligned with the Orhtomosaic.
  • The Virtual Inspector will present a shift.
  • The annotations are not synchronized between 2D and 3D.

Low alignment confidence

If less than 3 GCPs were found by the AutoGCPs algorithm, and the project does not have enough images to guarantee a good 2D alignment:

  • The user interface will display a low alignment confidence message in the 2D and 3D views.
  • The user interface will display the label Low_alignment_confidence.jpg in the Compare mode.
  • Warning icons will be displayed next to the error.png Overlays and warning.png Annotations layers.
  • The output coordinate system will be the same as the GCPs' one.
 
Warning: Under these conditions:
  • Ortho and DSM have low alignment confidence as there are not enough images. A correct alignment with the rest of the projects which belong to that site is not guaranteed.
  • The Point Cloud is not aligned.
  • The Virtual Inspector will present a shift.
  • The annotations are not synchronized between 2D and 3D.
  • A low-alignment confidence project might not be aligned with the others in the Compare mode.
  • A low-alignment project might show wrong values when included in a volume comparison.

Sites without GCPs

 

2D aligned dataset

If the project has enough images, the Ortho-alignment will be run.

  • The user interface will display the label  2D_aligned_dataset.jpg.
  • The output coordinate system will be the default WGS84 projected in UTM.
  • The Orthomosaic and the DSM will be aligned.
 
Warning: Under these conditions:
  • The point Cloud is not aligned with the Orhtomosaic.
  • The Virtual Inspector will present a shift.
  • The annotations are not synchronized between 2D and 3D.

Low alignment confidence

If the project does not have enough images to guarantee a good 2D alignment

  • The user interface will display a low alignment confidence message in the 2D and 3D views.
  • The user interface will display the label Low_alignment_confidence.jpg in the Compare mode.
  • Warning icons will be displayed next to the error.png Overlays and warning.png Annotations layers.
  • The output coordinate system will be the default WGS84 projected in UTM.
 
Warning: Under these conditions:
  • Ortho and DSM have low alignment confidence as there are not enough images. A correct alignment with the rest of the projects which belong to that site is not guaranteed.
  • The Point Cloud is not aligned.
  • The Virtual Inspector will present a shift.
  • The annotations are not synchronized between 2D and 3D.
  • A low-alignment confidence project might not be aligned with the others in the Compare mode.
  • A low-alignment project might show wrong values when included in a volume comparison.
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