Measure a diffuse laser point through a transparent surface

[andy.mcleod@unh.edu]

I need to image and measure laser light penetrating through acrylic surfaces. The laser will shine through the first acrylic panel, travel through cloudy water and then through a second acrylic panel. There will be 2 cameras, each mounted outside the tank looking at the respective panel. The laser point (circle) will be well defined on the first panel but variably diffuse on the second panel as a function of water quality.

I want to be able to capture video on 2 ethernet Axis cameras at 25fps (got that done) and measure the size of the circle, define its center and measure the lateral offset of the center of the 2 patterns as they appear on the acrylic. Assume my mechanical aligment is without error such that the imagery shows the XY offset to be calculated. I would rather work from the IMAQ data stream rather than capturing imagery and post-processing.

As I am new to the NI Vision world, could someone lead me to good references or vi's that will get me going?

[BruceAmmons]

Suggestion 1: Post pictures!!!

Will the laser be the only light in a dark room (or box, etc.)?  Or do you need to deal with ambient light as well as the laser light?

It will probably be difficult to define the edge of the circle and measure the diameter.  If it is fading from a bright spot in the center to gradually disappearing edges, it will be hard to say "That is the point where the edge is."  It might be easier to fit a 2D gaussian curve once you find the center and figure out the approximate size.  Once you have a gaussian curve, you can figure out total brightness using the area under the curve, and a diameter based on the sigma value.  Perhaps use 3 sigma as the diameter.

You can always calibrate offsets and diffusion levels using clear water, I would assume.

Bruce

[andy.mcleod@unh.edu]

Bruce-

We will have to deal with low level ambient light.

I have been working with Vision Assistant 2011 and have had little luck with gaining consistant results frame to frame. Once I open the image, I apply Color Threshold, Gaussian Filters, Binary Image Inversion, Advanced Morphology, and then Circle Detection gives me the data I was looking for. It appears to be working for the application in mind.

Thanks for your help.

Andy McLeod

Research Project Manager

UNH - JHC/CCOM