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<DIV><SPAN class=968565315-22082007><FONT face=Arial color=#0000ff size=2>Bit
hard to do in a PIC chip Wes</FONT></SPAN></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial
size=2>----------------------------------------------------------------------------</FONT></DIV>
<DIV><FONT face=Arial size=2>Andrew Rich VK4TEC</FONT></DIV>
<DIV><FONT face=Arial size=2><A
href="mailto:vk4tec@people.net.au">vk4tec@people.net.au</A></FONT></DIV>
<DIV><FONT face=Arial size=2><A
href="http://www.tech-software.net/">http://www.tech-software.net</A></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<BLOCKQUOTE>
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> johnstonwes@gmail.com
[mailto:johnstonwes@gmail.com]<B>On Behalf Of </B>Wes Johnston,
AI4PX<BR><B>Sent:</B> Thursday, 23 August 2007 1:31 AM<BR><B>To:</B>
vk4tec@people.net.au; TAPR APRS Mailing List<BR><B>Subject:</B> Re: [aprssig]
Proximity detection<BR><BR></FONT></DIV>
<DIV>Or you could use cosine corrected Pythagorean theorem.... </DIV>
<DIV> </DIV>
<DIV>dist=sqrt( (COS(average latitude) x [delta longitude] ^2 ) + [delta
latitude]^2). </DIV>
<DIV> </DIV>
<DIV>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</DIV>
<DIV> </DIV>
<DIV>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. </DIV>
<DIV> </DIV>
<DIV>Wes<BR><BR> </DIV>
<DIV><SPAN class=gmail_quote>On 8/22/07, <B class=gmail_sendername>Andrew
Rich</B> <<A
href="mailto:vk4tec@people.net.au">vk4tec@people.net.au</A>> wrote:</SPAN>
<BLOCKQUOTE class=gmail_quote
style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">
<DIV>
<DIV>
<DIV><SPAN><FONT face=Arial><FONT
size=2><SPAN>Gudday</SPAN></FONT></FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial size=2></FONT></SPAN> </DIV>
<DIV><SPAN><FONT face=Arial size=2>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 ?
</FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial size=2></FONT></SPAN> </DIV>
<DIV><SPAN><FONT face=Arial size=2>For example</FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial size=2></FONT></SPAN> </DIV>
<DIV><SPAN><FONT face=Arial size=2>I am at </FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial size=2></FONT></SPAN> </DIV>
<DIV><SPAN><FONT face=Arial size=2>2734.44 15206.20 and another object is at
</FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial><FONT size=2>2734.45 15206.20 - does not match -
outside the box<SPAN> </SPAN></FONT></FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial size=2></FONT></SPAN> </DIV>
<DIV><SPAN>
<DIV><SPAN><FONT face=Arial size=2>2734.44 15206.20 and another object is at
</FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial size=2>2734.44 15206.20 - match -
inside the box</FONT></SPAN></DIV></SPAN></DIV>
<DIV><SPAN><FONT face=Arial size=2></FONT></SPAN> </DIV>
<DIV><SPAN><FONT face=Arial size=2>I spose the size of the area depends on
how many significant digits of the position you use ?</FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial size=2></FONT></SPAN> </DIV>
<DIV><SPAN><FONT face=Arial size=2>You could make it tighter by comparing
more digits, and wider if you compare less ?</FONT></SPAN></DIV>
<DIV><SPAN><FONT face=Arial size=2></FONT></SPAN> </DIV>
<DIV><SPAN><FONT face=Arial size=2><SPAN>Comments
?</SPAN></FONT></SPAN></DIV></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial
size=2>----------------------------------------------------------------------------</FONT></DIV>
<DIV><FONT face=Arial size=2>Andrew Rich VK4TEC</FONT></DIV>
<DIV><FONT face=Arial size=2><A
onclick="return top.js.OpenExtLink(window,event,this)"
href="mailto:vk4tec@people.net.au"
target=_blank>vk4tec@people.net.au</A></FONT></DIV>
<DIV><FONT face=Arial size=2><A
onclick="return top.js.OpenExtLink(window,event,this)"
href="http://www.tech-software.net/"
target=_blank>http://www.tech-software.net</A></FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV> </DIV></DIV><BR>_______________________________________________<BR>aprssig
mailing list<BR><A onclick="return top.js.OpenExtLink(window,event,this)"
href="mailto:aprssig@lists.tapr.org">aprssig@lists.tapr.org</A><BR><A
onclick="return top.js.OpenExtLink(window,event,this)"
href="https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig"
target=_blank>https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig</A><BR><BR></BLOCKQUOTE></DIV><BR><BR
clear=all><BR>-- <BR>In theory there is no difference between practice and
theory. </BLOCKQUOTE></BODY></HTML>