Laser

There are two main tecniques to measure the distance with laser beam. One way is to pulse the laser beam and measure the time between emitted and reflected pulse. Second way is to beam laser constantly and then shoot the camera with special filter to measure how much the dot of the laser has moved on obstacle. The latter is the cheaper method as it does not need that special processor that is capable of sampling at nanoscale timeframe.

^{Figure 1: Distance measurement with angle detection method}

If laser beam is projected inside camera focal area then it is possible to resolve the distance using simple math. The optical axis of camera and laser beam should ideally be aligned perfectly. However, it is possible to add constant angle correction into math if angle is not perfectly aligned. A relatively simple algoritm can be used to find brightest pixels. This method assumes that the brightest pixels are laser dot which is the case usually indoors but not necessarely outdoors. Thats why red pass filter should be used to lessen disturbance of other light sources. When laser dot is resolved from image we can calcute the distance because the dot position in the image frame is known.

Distance D can be calculated with formula:

In this formula the h is constant distance between laser and camera. Theta is calulated from:

So the final equation would be:

To cut out the amount of data that needs to be processed the image frame can be cropped to save only pixel area where the laser dot can be.

References

https://sites.google.com/site/todddanko/home/webcam_laser_ranger