What is Correspondence and why is it important?

Correspondence defines a relationship between a CAD reference object and a test object (points or polygons). Basically, it shows and defines which points/polygons belong to the corresponding CAD surface. Each point/polygon on the TEST object can correspond to one face on the REF object. The correspondence is not typically of interest to users, but becomes relevant when AutoCreate Features or Evaluate GD&T Callouts does not perform correctly.

As a general guideline, use the following workflow to begin an inspection:

1) Load the TEST/REF objects into Qualify.

2) Perform a Best Fit Alignment. Note: Some may wish to use another type of alignment (i.e. Feature-based or RPS) and that is OK. This Best Fit Alignment is a preliminary alignment for correspondence purposes.

Click Apply to align the models.

3) Navigate to Tools>Mangage>Correspondence to Create/Edit correspondence.

4) Un-check Perform Correspondence Alignment (Best Fit) so that your previous alignment does not change. Click Create.

5) A color map representing which TEST polygons are corresponding to which CAD faces.

6) Check to make sure the correspondence is adequate by checking if any points/polygons overlap CAD face boundaries. Click on individual faces for a closer look. For example, the correspondence on this face needs editing. If GD&T were to be evaluated on this area later on in the inspection process with the correspondence like this, the results may be incorrect.

7) To remove this overlap, refer to the Edit section of the correspondence dialog. Enter a Relative % or Distance to "shrink the section with and click Calculate Shrink. The triangles will highlight a different color. Uncheck the Clipboard checkbox under Display in order to remove these polygons from view.

If any manual changes need to be made, click the Do Manual Selection checkbox, hold the CTRL key and select additional triangles. Click Accept when satisfied with the results.

Please see the related knowledge base article: How do I edit correspondence?

8) Click OK to exit the dialog. Continue on with the inspecition process.

The following functions can be greaty influenced by correspondence:

• Evaluating GD&T

  
  

• Partial Sections- Partial Sections use correspondence to determine what test data to include. Once the section is created there is no associatively, so correspondence creation/editing must be done before section creation. A poor correspondence may produce a poor partial section.

  
  

• Selection-based Best Fit Alignment

  
  

• Auto-Create Datums/Features

  
  

• RPS Alignment

  
  

• 3D Compare

  
  

• 2D Compare

  
  

• Wall Thickness

  
  

• Create Annotations

  
  

VERSION 11

Correspondence defines a relationship between a CAD reference object and a test object (points or polygons). Basically, it shows and defines which points belong to the corresponding CAD surface. Each point on the Test object can correspond to one face on the Reference object. The correspondence is not typically of interest to users, but becomes relevant when Tools>Auto-Create Datums/Features or Analysis>GD&T>Evaluate Callouts does not perform with sufficient precision.

As a general guideline, users should use the following workflow for their models:

1) Load the TEST/REF objects.

2) Do a Best Fit Alignment in Tools>Alignment>Best Fit Alignment

3) Go to Tools>Correspondence to Create/Edit correspondence. Un-check Perform Correspondence Alignment (Best Fit) so that your previous alignment does not change. Click Create. (Note: manual selection to modify correspondence is not automatable. Users can use 'Calculate Shrink', 'Max. Deviation' and 'Use Surface' if automation will be used)

4) Continue processing and analyzing the model.

The following functions depend on correspondence a great deal:

• Evaluating GD&T

  
  

• Partial Sections- Partial Sections use correspondence to determine what test data to include. Once the section is created there is no associatively, so correspondence creation/editing must be done before section creation. A poor correspondence may produce a poor partial section.

  
  

• Selection-based Best Fit Alignment

  
  

• Auto-Create Datums/Features

  
  

• RPS Alignment

  
  

• 3D Compare

  
  

• 2D Compare

  
  

• Wall Thickness

  
  

• Create Annotations