Creating a Mesh to Mesh Alignment

The Mesh to Mesh alignment functionality allows you to best fit align one mesh to another mesh which have been collected in two different reference frames that have some overlap. A typical example is two scans in two mesh commands, representing areas of a part that cannot be scanned in the same part orientation.

The alignment is done in two steps:

• A rough alignment, where pairs of points in the overlapping area of the two meshes are selected.

• A refined bestfit, which tries to bring the second mesh as close as possible to the reference mesh.

To create a Mesh to Mesh alignment, do the following:

1. Ensure that you have two or more Mesh commands in the measurement routine that you are using to align. These elements are required to align the two meshes.

2. Select the Insert | Mesh | Alignment menu option. You can also access this dialog box by typing the MESHMESHBF command in the Edit window’s Command mode between the ALIGNMENT/START and the ALIGNMENT/END commands. The dialog box appears:

Mesh/Mesh Alignment dialog box

For a complete description of the dialog box, see the topic "Mesh/CAD Alignment Dialog Box Description".

3. A temporary split-screen view of the two meshes appears in the Graphic Display window. You can use this view to visually see the alignment taking place. Select the first Mesh used as a point of reference from the Reference drop down list.

Split-screen view showing a mesh to mesh alignment

4. Use your mouse to manipulate and orient each view as needed to create the Point Pairs.

5. Perform the alignment:

1. Click the Compute button in the Auto section. You should only use this when you have a full scan of the external faces of the part. This automatically performs an alignment of the Mesh to the reference Mesh and also a refinement on the alignment as it's generating.

2. If the auto compute does not compute a good alignment, use the Point Pairs area to perform a rough alignment that brings the meshes close enough to each other. You can then refine the alignment further if needed. You should use this type of alignment if the mesh is not complete or it contains scanned data belonging to a fixture, table, or other similar feature.

• Click a desired number of points (at least three pairs) on each of the meshes on the overlap area. ONLY click points on the overlap area of the two meshes.

  

  Split-screen view showing selected MESH1 and MESH2 meshes

• The more points you take around the overlap area of the meshes results in an improved alignment. Click Compute to create the rough alignment.

3. Next, use the Refine Alignment area whenever you want to refine your alignment, thereby bringing the two meshes closer to each other. In order to get a good refined alignment, the two mesh points should be close enough to each other through the initial rough alignment.

   

   A sample rough mesh to mesh alignment that needs a refinement

1. Define the maximum distance between the points in the two meshes using the Maximum Distance box. The default value is 0 (zero). If the default value is used, PC-DMIS uses an internal default value related to the dimensions of the meshes.

2. Click Compute to refine the alignment.

6. If a portion of one mesh doesn't align nicely with the other, you can click the Undo button and recompute the alignment using the same type of alignment with additional parameters, or you can try a different alignment.

7. Once you're satisfied with the alignment, click Create. PC-DMIS closes the temporary split-screen view and places the MESHMESHBF command in the Edit window. For details on the MESHMESHBF command, see the "MESHMESHBF Command Mode Text" topic in the PC-DMIS Laser documentation.