Creating a Mesh/CAD Alignment

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

1. Ensure that you have an imported CAD model in the Graphic Display window and a MESH command in the measurement routine. These elements are required to align a mesh to the CAD.

2. Select the Insert | Mesh | Alignment menu option or select the Mesh Alignment button () on the Mesh toolbar. You can also access this dialog box by typing the MESHCADBF command in the Edit window’s Command mode between the ALIGNMENT/START and the ALIGNMENT/END commands. The Mesh/CAD alignment dialog box appears:

Mesh/CAD Alignment dialog box

For a complete description of the Mesh/CAD Alignment dialog box, see the topic "Mesh/CAD Alignment Dialog Box Description" in the PC-DMIS Laser documentation.

3. A temporary and split-screen view of the CAD model and the mesh appears in the Graphic Display window. You can use this split-screen view to visually see the alignment taking place. Select your point of reference from the Reference drop down list; usually, either the CAD model itself or a defined Mesh is available. The Mesh is aligned to the selected reference.

Split-screen view showing the CAD model on the top view, and the mesh on the bottom view

4. If you have more than one mesh in your measurement routine, choose the mesh from the Mesh list.

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 CAD 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. This brings the mesh close enough to the CAD if it's not already close. 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.

1. Click a desired number of points on the mesh.

2. Click corresponding locations on the CAD model.

   

   Split-screen view showing selected CAD (top) and corresponding mesh (bottom) points

3. The more points you take around the different areas of the model and mesh, the better the rough alignment.

4. Click Compute to create the rough alignment.

3. Next, use the Refine Alignment area whenever you want to refine your alignment, thereby bringing the mesh closer to your CAD model. In order to be able to obtain a good refined alignment, the mesh points should be close enough to the CAD points through an initial rough alignment.

   

   A sample rough mesh-to-CAD alignment that needs a refinement

1. Define the total number of random sample points to use in each iteration in the Total Points.

2. Define the number of iterations in the Maximum Iterations box.

3. Define the maximum standard deviation for the auto alignment execution between the points in the mesh and the CAD model using the Maximum StdDev box. When the auto alignment command is executed, if the standard deviation of the Mesh/CAD deviations is greater than the maximum value defined, you can select point pairs to get a better alignment. The default value of -1 is equivalent to an infinite allowed standard deviation.

4. Define the maximum distance of the points from the CAD in order for use in the best fit routines. The default value is 0. In this case, an internal max distance based on the size of the mesh is used.

5. Click Compute to refine the alignment.

6. If a portion of the mesh doesn't align nicely with the CAD, 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. If you have a surface model representing a sheet metal part, and you want to align to the offset faces, define an Offset value representing the constant thickness of the sheet metal part.

8. Use the Results area to see how well the mesh aligned with the CAD. Make any changes to the Offset or Refine Alignment values to improve the alignment if necessary. If any changes are made, be sure to click the Compute button to regenerate the alignment with the new values.

9. Once you're satisfied with the alignment, click Create. PC-DMIS closes the temporary split-screen view and places the MESHCADBF command in the Edit window. See the "MESHCADBF Command Mode Text" topic.

Example of a completed Mesh to CAD alignment