Thursday 6 June 2013

Laser Scanning a Room

Laser scanners are an amazing piece of tech which power everything from modern surveying to the self driving cars Google is developing. The way they work is surprisingly simple, they are actually just echo location, but using light.
  1. Point the laser at an object
  2. Send a pulse of laser light
  3. Measure the time the light takes to bounce back to the scanner
  4. Point at a new object and repeat
Most scan the whole of environment instead if just measuring the distance to single objects, and use a rotating scanner with a spinning mirror. 

So why don't the Google cars drive around dazzling people with lasers? Simple; they use infrared lasers instead. Near infrared has a wavelength of around 800nm and behaves just like the light we are used to. Imagine night vision not thermal vision. It is already common to use near infrared for communication using light that doesn't dazzle people, TV remote controls and mobile phone infra red ports use near infra red. 

This means, if Google's forecasts on the success of their self driving cars are to be believed, that in a few years time there will be a hidden world of laser scanning in action. Every time a Google self driving car goes past you will be scanned with infra red light. So what would that hidden world look like? 

I don't have a laser scanner, but I do have an infra red laser, an arm to wave it about with, an infra red camera, and perseverance. So let's fake a laser scan! 

This is what a room looks like when being scanned by a laser scanner (or at least a slightly wonky human imitation of one). Its not what a laser scanner sees, but what you could see if you could see in infra red and watched one in action. Pretty cool really. You can see the path the laser moves over as it scans, and the "shadow" of the scanner (ie. me!). You can just about make out the shape of the room, a coffee table and a sofa, by the way the path of the laser is distorted (some cheaper laser scanners actually measure this distortion to do the scan). 

So what about if there were multiple laser scanners in action together? Because they only look at a single point at any one time they wouldn't interfere with each other (unless they happened to try and scan the exact same point at the exact same time) so could all be on and working simultaneously. So here are two more fake scanning in action:

If these three scans were just piled on top of each other that would be pretty confusing to look at, so let's imagine that they use slightly different wavelengths (equivalent to colours) of light instead. 

This is the amazing result of having three (faked) and laser scanners in action at once. Pretty cool really. Even more scans starts to get messy, but the shape of the room really stands out. This is six scans combined with different colours for each.

Now imagine the future, a future where the infra red part of the spectrum starts getting busy as technology takes advantage of it. Picture a visible light photo of five self driving cars driving past a landmark. Basically just an advert for Google. Now picture the same thing, but in infra red. Now that could be a work of art.

For more images like this check out my Flickr set.

Geeky notes:
Laser scanners obviously aren't the only thing that lights up the near infra red part of the spectrum. The sun pumps out near infra red light which would swamp the scene with light, these photos will probably work better at night. Incandescent lights (ie. lights which aren't fluorescent, LED or energy saving), and anything else which is extremely hot (think flames and anything which glows red hot or hotter), also pump out infra red light. Fortunately as LED and fluorescent lights get more common the night time near infra red scene will get darker making the laser scanning pictures even more striking. On this topic this is why energy saving bulbs save energy, by producing less light at wavelengths that we can't see. 

Software used:
ImageJ: Photo handling and tweaking, composite image making.

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