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[aprssig] Proximity detection

Wes Johnston, AI4PX wes at ai4px.com
Wed Aug 22 15:30:38 UTC 2007


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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>


-- 
In theory there is no difference between practice and theory.
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