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Reverse Engineering to Surface Model

By reverse engineering with surface modeling, we can convert a 3D scan into a CAD surface model. The 3D scan exists as a polygon mesh (STL Format) which is reconstructed with NURBs surfaces to create a CAD model.

How Does the Reverse Engineering
to Surface Model Works?

The goal is to keep the deviation between the CAD surface model and the original 3D Scan as small as possible. During the reverse engineering to surface model, we do not optimize the 3D scanned part, which means that manufacturing defects are not corrected.

An optimization would be at the expense of the reverse engineering accuracy.

NURBS Surfaces are ideal for organically shaped parts with curved surfaces — like the body of a sports car, for example. With a reverse engineering software, the shape of the surface model can be directly and accurately molded from the underlying 3D scan. Because the surface model is molded directly from the underlying 3D scan, any manufacturing defects of the 3D scanned part are also transferred to the CAD surface model. A correction of these surface defects is not done because this would reduce the reconstruction accuracy.

The surface model which is created with a reverse engineering software is an empty shell. It is not a solid model. Only by closing it or giving it a certain thickness can a solid model be created.

Methods for Reverse Engineering
to Surface Model

Depending on the part’s geometry and future applications, we choose one of the following
methods for reverse engineering to surface model.

What else you need to know
about Auto Surface

With 3D scans of angular parts, auto surface sometimes unintentionally smoothes sharp edges.
The NURBS curve network is created automatically and randomly, ignoring the special properties of the part’s geometry.
Angular and uneven 3D scans lead to holes (missing surfaces). This means that in order to obtain a closed and watertight solid model, these must manually be repaired, which is a very time-consuming process.
CAD file is large. Due to the large number of surfaces created, the resulting CAD file is very big. This large file size can lead to high hardware requirements
The finished model cannot be further edited in CAD software.
All manufacturing defects on the 3d scanned part are transferred to the surface model. There is no correction of these defects, because this would reduce the reconstruction accuracy.

What else you need to know
about Boundary Fit

The manual creation of NURBS curves allows it to be flexibly molded to adapt the shape of the 3D scan.
The in-between NURBS patches are created automatically by the software.
Larger and more logically created NURBS patches are easier to work with.
Smaller file size, because the NURBs Surfaces are fewer and bigger.
Conversion into a solid model is possible.

More manual work, because the NURBS curves must manually defined and only the NURBS surface patches are molded automatically from the 3D scan.
Not as accurate as Auto Surface.
Deviation between 0.05 mm and 0.1 mm due to optimization.
The resulting STEP model cannot be further edited in a CAD Software. The only possible edits include deleting surfaces and redefining NURBs curves.
All manufacturing defects on the 3D-scanned part are transferred to the surface model. There is no correction of these defects because this would reduce the reconstruction accuracy.

Download the sample data

To give you an idea of the two reverse engineering to surface model methods, we have prepared examples for you to download. You can download the original 3D Scan and the CAD data, as well as the deviation analysis comparing the 3D scan and generated CAD model:

Get to know more

The result of this reverse engineering technique is a NURBS surface model. It could also be a solid model if the surface model is given a certain thickness or if it is closed and watertight. Surface modeling is primarily used for the reverse engineering of organically shaped parts with curved surfaces. It is not ideal for reverse engineering angular parts with many edges or parts with holes and threads.

CAD Surface Models are particularly suitable for CNC milling or FEM simulation. The reverse engineering data can be exported to the neutral CAD file exchange Formats (STEP, IGES or X_T). Every Surface model is delivered with an inspection report which compares the original 3D Scan to the reverse engineered CAD model. The inspection report shows the accuracy of the reverse engineering.

Frequently Asked Questions

What do you need for reverse engineering to surface model?

As a starting point for reverse engineering, the 3D data should be available as a polygon mesh (STL) or in a point cloud format. Alternatively, we at Holocreators can create a 3D scan for you. For this purpose, you can either send us your part by mail or we can 3D scan directly at your site.

How does reverse engineering to surface model work?

With the help of reverse engineering to surface model, the existing 3D scan is converted into a CAD format. For this purpose, the NURBs surfaces are molded from the underlying 3D Scan. There are two different variants: Either the reverse engineering is done fully automatically (Auto Surface) or the NURBs curves are defined manually and the surfaces in-between are generated automatically (Boundary Fit). Which variant is used is determined by the part’s geometry and your intended use.

Both variants result in a NURBs surface model that cannot be edited later.

In what format is the data provided after reverse engineering to surface model?

After the successful reverse engineering to surface model, the 3D data is output as a CAD surface model. Only under certain conditions can the surface model be closed and converted into a solid model.

The CAD model can be exported in the neutral CAD exchange formats STEP, IGES and X_T.

How accurate is the reverse engineering to surface model?

Reverse engineering with surface modeling is very accurate. On average, the generated surface model deviates only up to 0.05mm from the original 3D scan.

This high accuracy is achieved by the automatic molding of the NURBs surfaces from the underlying 3D scan. However, to achieve this high accuracy, manufacturing defects of the 3D scanned part are also transferred to the resulting CAD surface model.

Is there a deviation analysis that compares the 3D scan and the generated surface model?

Yes. After reverse engineering, we create a deviation analysis which compares the original 3D scan with the generated surface model. Any deviations are shown with a color scheme and markers that display how far the reverse engineering deviates from the underlying 3D scan.

Do you need help with your reverse engineering project?

Holocreators offers professional 3D-scanning and reverse engineering services. We would love to help you with your project and advise you on how to create a CAD surface model from a 3D Scan.

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