MIT technique 'reverse engineers' complex 3D CAD models

January 08, 2019 // By Rich Pell
Researchers at MIT (Cambridge, MA) have found a way to "reverse engineer" complex 3D computer-aided design (CAD) models that breaks them down into the many individual shapes they're made of.

The researchers used " program synthesis " - a process by which computer programs are generated from descriptions of their intended behavior - to break down CAD models into their primitive shapes, such as spheres and cuboids. Their technique, say the researchers, promises to make it far easier for users to customize CAD models for manufacturing and 3D-printing applications.

Currently, many of today's 3D models are created using constructive solid geometry (CSG), where numerous basic shapes - or "primitives" - with a few adjustable parameters can be assembled in various ways to form a single object. When finalized, the compiled digital object is then converted to a mesh of 3D triangles that defines the object's shape. These meshes are used as input for many applications, including 3D printing and virtual simulation. Customizing that mesh, however, say the researchers, is no easy task.

For example, adjusting the radius in one portion of the object requires individually tweaking the vertices and edges of each affected triangle. With complex models comprising thousands of triangles, customization becomes daunting and time consuming, say the researchers. Traditional techniques to convert triangle meshes back into shapes don't scale well to complex models or work accurately on low-resolution, noisy files.

Reversing the process that builds CAD models, the researchers' method disassembles CAD models into individual shapes that can be edited. As input, the system takes a 3D triangle mesh and first determines the individual shapes that make it up.

Program synthesis "crawls" through the shapes, trying to figure out how the shapes were put together and assembled into the final model. In doing so, it breaks down the mesh into a tree of nodes that represent the primitive shapes and other nodes detailing the steps for how those shapes fit together. The final shapes contain editable parameters for users to tweak that can be re-uploaded to the mesh.

"At a high level, the problem is reverse engineering a

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