Using Fast Alignment

You can quickly reposition a cloud of points or a mesh with respect to reference elements.

Fast Alignment is best used when there is a total correspondence between the object to align and the reference object. It also supports partial correspondence, provided the user activates portions of the object to align and of the reference corresponding to the overlapping areas.

Before you begin: Fast Alignment requires you have access to Digitized Shape Preparation.
  1. Select a geometrical set as Define In Work Object to store the output.
  2. From the Control section of the action bar, click Fast Alignment .
  3. Select the Cloud to Align (this is the cloud to reposition).

    It can be a cloud of points or a mesh.

  4. Select the References.

    A reference can be a surface, a cloud of points, a mesh, or a set of GSD points.

  5. Optional: Use Multi-selection and Hide/Show .
  6. Optional: Activate areas (Activate ) in the cloud to align and the references.

    By default, Fast Alignment computes the alignment on the whole cloud to align and on the whole references. However, in some cases (for example when the cloud to align and the references have the same global shape except on some portions), computing the alignment from the whole cloud to align may lead to unexpected results whereas computing the alignment from the areas that are identical leads to a better result.

    Note: Fast Alignment moves the whole cloud to align in both cases.

  7. Select With Pre-Alignment if the object to align is far and not aligned at all with the reference object.
    Fast Alignment performs a prepositioning based on bounding boxes before the finalization step.
  8. Click Partial Deviation Analysis to confirm the result of the fast alignment on the points subset taken into account for the computation.
    Partial Deviation Analysis provides a first validation of the alignment, with better performances.
  9. Select With Frozen Axis to freeze a direction that you know is already good.
    1. From the list, select the direction to freeze.
  10. Decide to keep the initial cloud or not.

    By default, the Keep Initial check box is selected. Fast Alignment

    • Keeps the initial cloud to align as such.
    • Copies this initial cloud to align and displays it in the tree.
    • Aligns the copy of the initial cloud with the references.

    1. Clear this check box if you do not want to create a copy of the initial cloud to align, for example because of its size. Fast Alignment aligns the initial cloud itself with the references.

      Note: To avoid inconsistencies, you cannot clear the Keep Initial check box in the following two cases:
      • When the geometry of the cloud to align is shared by other cloud elements, for example when the cloud to align shares points or vertices with another cloud without any parent/child relationship between them. Clearing the Keep Initial check box would move the other cloud together with the Cloud to Align, which you do not want to.
      • When the cloud to align is a feature, for example a Generative Shape Design transformation feature.

  11. Click Apply.
    A progression bar is displayed. Click Cancel to stop the computation at any time. The cloud to align or its copy is moved toward the references.
  12. Click More to display the Statistics.

    • Number of iterations
    • Number of points used in statistics calculation
    • Minimum deviation
    • Maximum deviation
    • Standard deviation.