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Index › Programming Questions & Help › Electronics,  Serial Library › Ways of measuring distance from a wall to people
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Ways of measuring distance from a wall to people? (Read 1625 times)
nickdatz
Ways of measuring distance from a wall to people?
Nov 8th, 2006, 8:22pm  
Hi all,
I need to measure distance from a wall to several people in an empty room for an installation.  

My goals are:

- Track small changes in distance effectively (i need good measuring resolution).
- Be able to track fast changes (i need fast reaction time)
- The system should be ideally able to track distance to several people, not necessarily each individual, but at least groups of people.

My first thought was that it could be done using computer vision (jmyron in processing or eyesweb), but it seems that this method is very cpu-consuming, too dependent on the quality of the camera and lightning, and i doubt about the resolution i'll be able to get. Some people suggested using an ultrasonic rangefinder connected to an arduino board. I have never done anything similar, so I have lots of doubts...

0) Have you done anything similar?
1) Are there any other options for this task? Do you think it can be done in a better way?
2) How difficult will it be to implement this using arduino?
3) How do you think I should deal with the requirement of being able to track distance to several people? Would I need more than one sensor? How sensitive are them? How directional? What's the range they cover? Where can I get them?
4) How do I connect the sensor to arduino?

I hope you can help me.
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lars
Re: Ways of measuring distance from a wall to peop
Reply #1 - Nov 13th, 2006, 8:08pm  
I think a camera solution will still be the best and the simplest. You could place a camera that looks down from above  and keep the floor white. You don't need any clever computer vision software, but just to iterate through the pixel array for each frame from the camera to find the edges of where people are standing (assuming that there is enough contrast between the white floor and the people). It might be a good idea to use a daylight filter - so the camera only sees infrared light. It should be fast enough if you run it on a decent pc and maybe don't use the full resolution of the camera.

I have worked with both infrared and ultrasonic rangefinders before - and if you want to use several to cover a larger area it becomes a pain. Although you can get good resolution from each module - it is limited how close you can place the modules beside each other before you start to get interference.

/lars
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nickdatz
Re: Ways of measuring distance from a wall to peop
Reply #2 - Nov 14th, 2006, 4:49pm  
In your experience, how close can you place ultrasonic rangefinders to each other, and how directional is the ultrasonic beam?
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