[aprssig] Proximity detection

Andrew Rich vk4tec at people.net.au
Wed Aug 22 10:54:09 CDT 2007

Bit hard to do in a PIC chip Wes

Andrew Rich VK4TEC
vk4tec at people.net.au

  -----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

  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.


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

    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

    aprssig mailing list
    aprssig at lists.tapr.org

  In theory there is no difference between practice and theory.
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.484 / Virus Database: 269.12.1/965 - Release Date: 21/08/2007
4:02 PM
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.tapr.org/pipermail/aprssig/attachments/20070823/32a419f2/attachment.html>

More information about the aprssig mailing list