Aligning Clouds using Spheres

This task shows you how to align clouds of points to other clouds of points, using sphere recognition.
Open the Reposition1.CATPart model the from the samples directory. It consists of two clouds of points with three spherical  tags on each. These tags have been created during digitizing in order to align the two clouds in future operations.

  1. Click the Align using sphere  icon  . The Alignment dialog box is displayed.

  1. Pick the cloud to move (in fact the output cloud is a moved copy of the initial cloud, which can then be hidden if necessary), then the target cloud.

  2. Then pick the spheres on the first cloud, click OK to validate them. 

    If you know the radius of the spheres, check the Constrained check box and enter the radius in the input field. Digitized Shape Editor  will compute the spheres with that radius.

    If you do not know the radius of the spheres, click the first sphere. Digitized Shape Editor  will compute this radius and update the input field accordingly. Then you may check the Constrained box and select other spheres that will have the same radius.

    Use the Selective Display option to make the definition of the spheres easier: when this option is active, only the cloud where you should define the spheres is displayed. Once you are finished with the first cloud, it is hidden and the second one is displayed.

     

  3. Repeat the sphere selection step on the second cloud, click OK to validate them.

 
The input cloud is duplicated and this copy is moved towards the target. This new cloud appears in the specification tree. It has the name of the input cloud, with its index increased by one. An element Axis_Systems is also created in the specification tree, that contains the reference axis system and the target axis system. These two axis systems can be used in an Axis to Axis transformation with other geometrical elements (i.e. replay the alignment).
While aligning clouds, you can use the function Distance analysis to check the output accuracy. The target will be the output cloud. Since a new output cloud is generated at each alignment, you should repeat the distance analysis with each new output cloud.
We recommend that you pick the sphere in a direction orthogonal to the part to process, i.e. along the green axis and not along the black axis in our example : 

For an easier sphere recognition, we recommend that you pick in the middle of the sphere, not at the edge.

If you use 3 spheres, they should not form a isosceles nor an equilateral triangle (the system could not find out the right solution between the two or six possible solutions).

The result entity has the same structure as the input entity: scans, grids or polygons.
Undo is available on the selection of spheres.

 

Back Up Next