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[aprssig] Proximity detection

Andrew Rich vk4tec at people.net.au
Wed Aug 22 15:54:09 UTC 2007


Bit hard to do in a PIC chip Wes


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Andrew Rich VK4TEC
vk4tec at people.net.au
http://www.tech-software.net


  -----Original Message-----
  From: johnstonwes at gmail.com [mailto:johnstonwes at gmail.com]On Behalf Of Wes
Johnston, AI4PX
  Sent: Thursday, 23 August 2007 1:31 AM
  To: vk4tec at people.net.au; TAPR APRS Mailing List
  Subject: Re: [aprssig] Proximity detection


  Or you could use cosine corrected Pythagorean theorem....

  dist=sqrt( (COS(average latitude) x [delta longitude] ^2 ) + [delta
latitude]^2).

  of course the answer you get is in degrees and you have to convert that to
miles or km.  1 degree = 60 miles, 1 degree = 111km

  I've checked it with a spread sheet years ago, and it works to within .1
of a mile out to 100 miles at 33° latitude.  It does NOT work for great
circle distances... it will choke on antipodal points for example.  But it's
good for your general vicinity.

  Wes


  On 8/22/07, Andrew Rich <vk4tec at people.net.au> wrote:
    Gudday

    If you get a micro, and you know from a GPS where you are, and then you
pick up another position, one would assume you can then apply a basic "is
there anyone in my box" calculation ?

    For example

    I am at

    2734.44 15206.20 and another object is at
    2734.45 15206.20 - does not match - outside the box

    2734.44 15206.20 and another object is at
    2734.44 15206.20 - match - inside the box

    I spose the size of the area depends on how many significant digits of
the position you use ?

    You could make it tighter by comparing more digits, and wider if you
compare less ?

    Comments ?

    ------------------------------------------------------------------------
----
    Andrew Rich VK4TEC
    vk4tec at people.net.au
    http://www.tech-software.net




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