I'm attending the RAPID and 3d imaging show here in Atlanta, Ga. Evidently, the term "rapid" as is "rapid prototyping" has been replaced by the more descriptive term "additive manufacturing." As you recall, this implies the building of prototypes and functional parts layer-by-layer as opposed to, say, cutting parts from a CNC machine. In any case, Michael Mock of INUS Technology Inc., which provides Rapidform XOR software which takes scanning data and makes it into a useful 3D model in CAD.
According to Mock, scanning data can be in the form of a point cloud or a mesh. When it comes to point clouds, scanners basically just collect "dumb" points in space (which CAD systems cannot understand). Most CAD packages treat each end point as an object and so when you import millions of these, the CAD software merely crashes.
Things get easier when the points are connected in space to create a mesh. But the problem is that mechanical CAD can't really use meshes. (Industrial software such as Maya can, however.)
Next in the so-called "hierarchy" of geometry as Monk puts it -- that is, more easily understood by CAD -- are curves.
After that are surfaces. CAD can work with surfaces. For example, you could scan someone's face, make an STL file, and then 3D print a bobble head of that person's face. But surfaces are generally not that useful in the mechanical environment.
So what is the top of the geometry food chain as far as CAD packages might be concerned? Features. CAD understands these well because they are created from sketches, which, hopefully comprise good, clean geometry.
When it comes to making a point cloud useful for CAD there are two approaches, says Mock. One: you can have a standalone scanner and standalone software that work together. Or, two: you can have an integrated solution.
In the first approach, you would create a useful proxy of scan data and then "throw it over the wall" to CAD. The designer would then put the pieces together to design the part.
The integrated solutions, on the other hand create geometry directly from scan data. The two are iteratively overlaid constantly for comparison and checking. The benefits are a familiar workflow and the approach leaves the major CAD system free 90% of the time so designers can be doing other work.
An independent analyst compared various CAD software that claims to include reverse engineering. Rapidform XOR came out heads up on the top of the list, he says.