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    using a logitech c615 webcam for distance measurement experiment

    Hi,

    I am trying to work out an experiment for determining distance of a target placed 800 mm away. The experiment is something like this.

    A sharply focussed laser beam is targeted at a target (grey black in colour and non reflective), the laser beam is at an angle, a webcam like the Logitech C615 is placed directly opposite the dot.

    The webcam captures the image, and is transferred to a PC, a program in the PC is used to get the position of the laser dot. By knowing the angle of the beam and the distance between the laser and the webcam, the distance of the target can be calculated, now when the distance of the target is increased the position of the laser dot in the image shifts, by working out a formula using the shift, the angle of the beam and other constants I think the distance can be calculated ??

    I need to know what would be the accuracy of the distances ? I am looking for 1-2 MM accuracy (ie: its should be possible to detect shift in target distance of at least 1-2 MM) , is this possible with this method ?

    The webcam has a max resolution of 8 Mega pixels,and can capture steady video at 1080p at 15fps. Do you think the Logitech C920 should be better it has 15 Mega pixels, or is a GoPro camera better ?

    thanks
    a

    •   Alt28th August 2016, 05:10

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    Re: using a logitech c615 webcam for distance measurement experiment

    use a laser detection diode [forget the proper name!] for the detection.................NOT a webcam

    Google................several such circuits exist



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    Re: using a logitech c615 webcam for distance measurement experiment

    use a laser detection diode [forget the proper name!] for the detection.................NOT a webcam

    Google................several such circuits exist
    Did you mean a CCD ? CCD is normally used for such applications but I was hoping something cheaper would work. CCD also need a suitable lens

    thanks anyway



    •   Alt28th August 2016, 13:44

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    Re: using a logitech c615 webcam for distance measurement experiment

    Hi;
    I am not expert on that, but a few comments. Hope helpful.
    For camera digital resolution selection i think you should consider how many pixel will correspond your laser dot in image. You need some calculations to do so (based on webcam parameters). Have a look below;
    https://www.learnopencv.com/approxim...phone-cameras/
    http://digital.ni.com/public.nsf/all...257D00007305D5

    PS: Another point, as i understand you will tilt the laser angle till you see the laser dot on target. Since you know laser angle and distance between laser and camera, you will calculate object distance by simple geometry rules.
    Here let say target at 800mm, laser to webcam 50mm, then laser tilt angle should be arctan(800/50)=86.42deg.
    Let say object at 802mm, then tilt angle arctan(802/50)=86.43deg.
    Can you tilt laser so sensitvely? 0.01mm.
    One solution you should place laser far away from your webcam.

    Good luck


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    •   Alt28th August 2016, 15:33

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    Re: using a logitech c615 webcam for distance measurement experiment

    Can you tilt laser so sensitvely? 0.01mm.
    One solution you should place laser far away from your webcam.
    Those links were very useful...

    I worked most of the calculations involved, the part where I was now stuck is finding out the scaling of the pixels to the actual dimension. I think those links will help clear this..


    thanks
    a



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    Re: using a logitech c615 webcam for distance measurement experiment

    One consideration is the response speed of a webcam............I doubt it is as fast as a photodiode


    You may have to adjust for the latency


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    Re: using a logitech c615 webcam for distance measurement experiment

    After reviewing the photo diode links in post #4, I really ,don't know which measurement principle is addressed with "laser detection diode".

    Laser distance measurement instruments and OEM modules with 1 mm accuracy are widely available these days and are promising absolute distance values without adjusting a triangulation setup. The systems are implementing time-of-flight respectively high frequency phase shift measurement. A fast photodiode is part of the design, but the electronic is rather complex.


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