Align Scans to CAD - Point Based Alignment with BuildIT Construction

Tutorial Download

If you would like to download the file used in this article, download the accompanying Training Data and extract its contents to a folder on your PC.

Navigate the Set Views

Open the “Module 8.1.buildit” file by selecting “File> Open” and navigating to where the file is saved.

• In the BuildIT file for this exercise, there are also other set views to aid in the exercise. All of these are found under “Views” in the Manager.
  • To activate these views, right click the view and select “Restore View” or double left click on the intended view.
    
• To set a view similar to the already created “CAD View.”
   
• Click View > Set View. Manipulate the clipping box to create a similar view, hiding exterior information.                       
  • This will result in the following view, also called “CAD Data” in the Manager.
    
    

Selecting Nominal Points on the CAD Surfaces

• A minimum of three datum, or control, points need to be selected on the model. This will allow the software to accurately align the scan data to the model. For this exercise, we will choose three points spread out in our area of interest on the model. The points each have views in the Manager, as shown below.
  
• Use the established views to create the nominal, or datum, points.
  • Activate each view, as described in the section Navigate the Set Views.
  • Use “Construct > Point > Point 3-Plane Intersection…”.
  • Name the points in the way shown above, “DATUM 1 – CAD”. This will make the alignment easier in later parts of the module.
  • Select the three surfaces for each point.
  • Ensure “Create as Nominal” is selected for the points on the model.
  • Select Apply.
  • Create the other points in the same fashion as above, at the locations shown.
    

Creating Measured/Actual Datum Point in Cloud

• Now that the points have been created from the CAD data, the points will need to be extracted from the scan data. There are views created, as shown below, that will directly view the same points in the cloud.
  
• Activate the set view “Datum 1 – Cloud” and extract three planes.
  • Select “Refine > Extract Surface” or select the command from the toolbar.
  • Using the mouse, select and drag on the cloud points to create a plane.
  • Create 3 planes as shown below.
    
• Create measured point.
  • Select “Construct > Point > Point - 3 Plane Intersection”.
  • Name the point Datum 1 – Cloud and select all three surface planes extracted.
  • Deselect nominal point and select Apply.
    
• Extract the other two datum points using the corner point filter.
  • Activate the “Datum 2 – Cloud” view.
  • Select “Refine> Extract Corner”.
  • Name the point “Datum 2 – Cloud”.
  • For the “Seed Points”, use the “Point: Measurement” filter.
  • Select near the corner and the corner point will be extracted.
  • Select Apply.
  • Repeat for Datum 3.
    

Best Fit Alignment

• Use the Best Fit Alignment to align the CAD data with the extracted data.
  • Select “Measure > Alignment and Scaling > Best Fit Alignment”.
  • From the manager, select the “Datum 1 – Cloud” point for “Measurement”.
  • From the manager, select the “Datum 1 – CAD” point for “Nominal Geometry”.
    • The “Point: Nominal” filter will help with this selection.
  • Select “Add Plane”.  
  • Repeat for Datum 2 and 3.
    
  • Final Result:
    

Recap:

Congratulations, you have completed the Align Scans to CAD – Point Based Alignment! By now you should have a grasp of how to:

• Importing scan data and CAD data and align them together.
• Open BuildIT, opening a BuildIT file and manipulating the viewport.
• Create Plane and datum points.
• Align your CAD (*dwg) file to Laser Scan data using Point Based-Alignment.