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precise positioning system

Discussion in 'General Electronics Discussion' started by mitgha, Aug 25, 2012.

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  1. mitgha


    Aug 25, 2012
    Please help me to have an idea if the following is possible:

    I need a positioning system for flying small aircraft,
    I want to position them with high accuracy and fast.

    The specification would be as follows:

    High speed: about 20 reads per second!
    Hight precision: 1cm
    Outdoors but in open field, no buildings.
    Area covered: 2km by 2km.

    My first thoughts are about an RF or Sonar system.
    Transmissions done from the aircraft with couple of receivers
    positioned on a grid of 500meter on the surface.

    Thanks for your help.
  2. CocaCola


    Apr 7, 2012
    This verges on military type accuracy, I hope you have huge budget...

    Sound takes about 3 seconds to travel 1km, making sonar useless in a 2km x 2km area, the latency would put you WELL out of the 1cm accuracy unless the object was stuck in molasses, and only moving 1cm say every 6-10 seconds...
    Last edited: Aug 25, 2012
  3. mitgha


    Aug 25, 2012
    Dear CocaCola,
    Thanks for your rapid answer.
    Yes you are right, I was not also very comfortable with sonar.
    My budget is about 5000usd or euro, so
    not very small but not also military.

    Do you think with high quality RF is this possible within 5000
    for the whole system?
  4. CocaCola


    Apr 7, 2012
    Nope, I do not think $5000 will get you anywhere near the specifications you desire... You could probably get a crude RF positioning system up and running for that amount if you get lucky... But IMO no way will you get anywhere near 20 measurements per second with 1cm accuracy in a 2km x 2km x (what ever height) area of a object moving at a swift pace...

    Again I implore you to consider the latency of an RF triangulation system and the practicality, just for a minute just try to wrap your mind around how precise you will need to measure that RF signal (at the speed of light) to derive at a 1cm resolution... What is the timing deviation from 2345cm to 2346cm, since that RF signal is traveling about 29,979,000,000cm/s? You are down in the picoseconds measurement range there, not much room for error if you want to hold 1cm resolution :) Now consider processing those calculations and measurements 20 times a second if you can...
    Last edited: Aug 25, 2012
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I've done some work with people who do aerial photography and other remote sensing requiring high positional accuracy.

    I don't believe they get anywhere near this accuracy (especially in the Z axis).

    Can you tell us a little more *why* you need this (especially 20 reads per second). In the situation I described above, they would take readings far less frequently than this, and would interpolate between them. Aircraft don't change velocity very quickly.
  6. davenn

    davenn Moderator

    Sep 5, 2009

    I work with hi tech and seriously expensive GPS systems and it wouldnt even be able to track with that accuracy on an object moving so fast with that accuracy

    I can get down to 1cm accuracy on slowly moving objects and 5mm on fixed objects

    Last edited: Aug 26, 2012
  7. Electrobrains


    Jan 2, 2012
    Hope this is not some private military project...
  8. mitgha


    Aug 25, 2012
    CocaCola: Yes, you are right, it is not possible with RF to get close to that specifications. The main problem is that a signal with wavelength of 1cm is
    30GHz, now for the proper detection of the signal one needs even higher frequency.
    Which pushs the signal in the range of 300GHz which is not RF really, it is more
    microwave or low frequency infrared.

    Steve: Well, as I mentioned in my first post
    "I need a positioning system for flying small aircraft,
    I want to position them with high accuracy and fast. "
    The speed and accuracy requirements I wrote, just would give me peace of mind to
    focus on errors and problems in other components of my system.
    Anyway now I see that the main part is exactly that and probably I should bring the
    requirements down to what I exactly need.

    Davenn: Well the public GPS is not really designed for the purpose of accuracy and speed. So no hope with that.

    Electrobrains: No it is not.
  9. mitgha


    Aug 25, 2012
    I think the best way to get to this is by visually tracking the object.
    First as CocaCola mentioned in his first post the ultrasound is not applicable
    due to its slow speed.
    So one should design it with electromagnetic waves.
    As I mentioned in my previous post one needs then about 300Ghz or higher.
    So it should be at least infrared. working with infra red is hard for me and I think the
    equipment for it are more expensive than for example visual light equipment.
    So we come to Visual range light.

    I think a servo precise moved camera with computer controlled zoom and focus with an
    object tracking software would do the job.
  10. Electrobrains


    Jan 2, 2012
    I doubt you will be able to do that with any affordable camera system. It would need to be super fast and have very high resolution. Added to that you would need some image recognition and analyzing software that can handle the information.

    Maybe you can use radar. There is a frequency band opened up to Long Range RADAR (76/77GHz) Systems, where commercial components are available. Mainly intended for the automotive market, but sure also possible to use in other areas. You can search on Google and find a lot of information.
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