Request a Demo!
1000 characters left


Comparing Actual and Nominal CAD Data in GOM Software


ATOS technology enables 3D inspection analysis, an extremely powerful tool for digital engineering. It is important to understand the inspection basics for comparing a CAD and an actual mesh, which is easy to do in GOM Software. The software generates a color map, otherwise known as a surface comparison, that supports the visualization of 3D scan data, which serves as a guide throughout the analysis. This guide will teach you the basics of comparing actual and nominal CAD data in GOM Software.


Step One: Import CAD and Mesh

Begin by opening GOM Inspect Suite 2020 and creating a new project. Then import both the CAD and the mesh for further inspection. There are a couple of different ways to import items into the software. The easiest way is to drag and drop them from the folder where they are contained. Once you drag and drop the mesh into the workspace, the software gives the option to create a new part which means the software creates a part container in the Explorer where the mesh will live. Following the same steps with the CAD prompts the software to add it to the part, which adds it into the same part container. You'll want them in the same part container since you'll need to compare the two. Any elements or inspections you create will reside in this part container with this CAD in the mesh.



Step Two: Apply a Prealignment

Notice that the mesh is clearly not positioned appropriately at this stage because no alignment has been applied yet. You'll need to apply an initial alignment, also known as a prealignment. This type of alignment is a global best fit. The software evaluates the CAD and mesh to discover how the mesh can best fit the CAD with the least deviation across the whole part. You can see the deviation listed in the prealignment dialog box. Applying the prealignment brings the CAD and the mesh closer together so you can start building some of your inspection or create additional alignments as needed later. After you hit OK on the prealignment dialog box, the CAD and the mesh will be aligned, and you can begin some inspection.


Step Three: Perform a Surface Comparison

First, hide the mesh, so it's not over the CAD. One way to hide the mesh is to hit the eyeball icon next to it or click on it while hitting the I key for invisible. Next, perform a surface comparison (color map). To begin this step, navigate to the surface comparison button on the toolbar. Selecting this button prompts two options.


Surface Comparison on CAD

For this example, choose surface comparison on CAD, which provides the surface deviation between the CAD and the mesh and displays it on the CAD. Next, set the max distance and the tolerance. The max distance is how far the software will search for the mesh off of the CAD and look for that deviation. If the max distance is set too low, the software won't search anymore, and the area will turn gray, so it's important to make sure the distance is high enough than any deviation you might see across the part. If the software displays color over the part, you're in good shape.


Next, enter the tolerance. Leave it at .10 for this example. Then, adjust the legend by navigating to the top of the colored bar, selecting the top number, and changing it to .50. Closing the bracket button provides a plus or minus .50 legend and provides more color across the whole bar, which helps you visualize it. You can make other adjustments to the legend however you want.


Surface Comparison on Actual

Next, perform the other type of surface comparison to see the difference. To begin a surface comparison on actual, create it with the same parameters. Notice that it looks very similar, and the color is the same. While the actual inspection is the same, the calculations and what it's displayed on are slightly different. If you drag the surface comparison on CAD in, you can see what it looks like, versus the surface comparison on actual. Each option provides a different way to visualize the color. You can overlay that color onto your CAD model or on your actual mesh, but the inspection will ultimately give you the same result. This example will use the surface comparison on CAD.


Step Four: Apply Deviation Labels

The next step is to drop deviation labels on the part. Moving along the toolbar, you'll see the third option is pointwise inspection. Select that, then navigate down to deviation labels, and you'll see a window popping up at the bottom. Whenever you're in a function like this, this window shows you what the different clicks do in that particular function. In this case, the software indicates that holding CTRL while hovering over the part gives you a preview of the deviation at that point. If you want to create the element, use CTRL and left click, then the software will drop the point at the cursor's location. Use the Escape key, or right-click to cancel or finish and then proceed with the inspection.


Step Five: Create a Report Page

Create a report page if you want to save this view to present the data later. Begin by clicking the camera icon at the top of the screen called Create Report page. A window will then pop up, prompting you to enter a title. For this example, name it Surface Comparison. If you select the pencil icon in the center, you'll be able to move the page around and position it however you want. Then hit OK twice to save the report page to view and edit later.


Step Six: Create an Inspection Section

An inspection section is very similar to a surface comparison. However, the big difference is that instead of looking across the whole surface and getting that color representation, you'll only take a section cut and only look at the surface deviation along that section cut. Begin by clicking and dragging the CAD into the view to make it exclusive and hide everything else. Next, locate the inspection section button on the toolbar. Clicking on that selection will display two choices: On CAD and On Actual. For this example, select Inspection Section on CAD and choose the reference plane to be the X, Y or Z. In this case, a z cut works best.

The next step is to position the section. There are a couple of different ways to move the section around. One way is by using CTRL and left-click. The section will stay in Z normal because that's the reference plane, but the section where you click will be dropped. This method of moving the section is ideal for when you have a specific area you want to cut that section through. However, if you don't want to do it that way, you can hover over the Position section in the dialog box and scroll with the mouse wheel to move that section up and down. You can also type in a position if there's a particular position that you want the section cut. Once you've made your selection, hit Create and Close.


There will now be color representation along the section cut representing the surface deviation. However, if you do a side view, it's a little bit difficult to see, so use a feature called Clipping at Plane, which is located at the bottom. When you select that and hover over the section, two green icons will appear, allowing you to choose which section of the part you want to clip out around that section cut. When you perform this function, know that you're not deleting anything but selecting sections for viewing. To deactivate this function, click the function in the corner that says, "Click here to Deactivate." Now you can see the section cut and surface deviation along that slice while in front view.


Step Seven: Drop Deviation Labels Along the Section Cut

Suppose you want to drop deviation labels along the section cut. In that case, you can click on the section so it's highlighted, then go up to pointwise inspection, and select the second option, equidistant deviation labels. This function allows you to enter a specific distance then places points spaced out equally by that set distance. For this example, set it to every 10 millimeters, and the software will drop the deviation label along this section every 10 millimeters. You can still add additional points to the section as necessary.


Create a report page of the inspection section by hitting the Create Report Page button. For this example, name it "Inspection Section," then hit OK. If you need to deactivate the inspection section, click in the top right to have the whole part back. When you switch your workspace to reporting, you will see the two pages available for further viewing and editing.


Step Eight: Keep Improving Your 3D Inspection Efficiency with GOM Software

Taking a blank project through inspection for display on report pages is quickly done within a few clicks. To summarize, first import both the CAD and the mesh and align them using a pre-alignment, which is a global best fit. Once aligned with the simple click of a button, create both the surface comparisons and the inspection sections and put that information into easy to interpret report pages. This quick and simple process is just one of the many valuable benefits of 3D inspection that GOM Software supports. Plus, quickly generating information about the part can ultimately save time and money. If you'd like to learn more about how to make your 3D inspection process more efficient, contact a Capture 3D expert today!

© Copyright 2022. Capture 3D, Inc. All Rights Reserved.