Tuesday, October 4, 2011

Overview of 3D vision applications

Are you familiar with the game of “Blemish” often played by insecure managers? Its where, no matter how good your work is, the boss finds some tiny flaw to pick away at. It has a pretty demotivating effect and I hate it, so I’m going to play it now.

Over on the AIA website (www.machinevisiononline.org,) you’ll find an interesting article by Winn Hardin titled “Through the Looking Glass: Differences Between Large and Small 3D Vision Applications” (September 21st, 2011.) It’s a little too tilted towards the Gocator from LMI for my tastes, but otherwise it’s a good reminder that 3D covers the gamut from microns to meters.

I do however have a problem with one sentence. Now this could be my lack of understanding, and if so please point out my error, but I am perplexed. Winn says “Structured light solutions … are well-suited to high-precision 3D imaging applications, as well as for isolating hard-to-image features such as the bottom of a screw hole where the pitch is so steep that it’s difficult to accommodate the different views from a two-camera stereovision solution.”

My understanding of structured light is that it requires an angle between camera and light (typically it’s a sheet of light, like a line from a laser.) So if the light is coming in at 45o, doesn’t that make it well-nigh impossible to check the depth of a screw hole?

If I’m wrong I would like to know, because I do have a few applications that would benefit from measuring deeply recessed features.


Anonymous said...

I thought structured light referred to projecting some 2d pattern onto the target surface, and then using the deformation of the pattern to establish geometry.

B Grey said...

Valid point, although my interpretation is that structured light refers to any technique that involves examination of where projected light impacts a surface. Thus the various grid and strip projection methods are structured light, as is the sheet of light method.

Any other comments on this?

Spencer Luster said...

Yep, Moire methods (involving 2D pattern projection) of surface profiling can definitely be accomplished with small angles between the projector and the receiver. I used to work with a company that specialized in this.

I haven't run across such micro-Moire systems that might be used for looking at the bottom of screw holes. I confess, however, that I haven't paid attention for awhile. There's also the problem of properly imaging such a possibly specular surface, but where there's a will...