<div dir="auto">Thanks Mike. Very informative. </div><div dir="auto">I don’t expect an exact answer (2). Even the Euclidean distance will do in my case. </div><div dir="auto"><br></div><div dir="auto">/Frank</div><div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Wed 26 nov. 2020 - 06:14, FRENCH Mike <<a href="mailto:mike.french@thalesgroup.com">mike.french@thalesgroup.com</a>> wrote :<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
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<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">1. What is the overall extent of the points?<u style="font-family:Calibri,sans-serif"></u><u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u style="font-family:Calibri,sans-serif"></u> <u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">2. Do you need the exact answer?<br>
e.g. will there be many points close together and you <i style="font-family:Calibri,sans-serif">have</i> to get the correct one;<br>
can you assume a spherical Earth, not model the exact geoid shape (WGS84,etc.)<u style="font-family:Calibri,sans-serif"></u><u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u style="font-family:Calibri,sans-serif"></u> <u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">3. Does the region include the areas around the poles or crossing the 180 longitude ‘dateline’?<br>
<br>
If (1) is ‘small’ or ‘a few 100 km’, and (2) and (3) are NO, then there are some simple methods …<u style="font-family:Calibri,sans-serif"></u><u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u style="font-family:Calibri,sans-serif"></u> <u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">If it is a localized region near the equator (e.g. within Singapore) you can use the Euclidean formula directly.<u style="font-family:Calibri,sans-serif"></u><u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u style="font-family:Calibri,sans-serif"></u> <u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">If it is a localized region, you can assume the ‘2D tangent plane projection’ Euclidean approximation.<br>
Take the middle value for the latitude, <i style="font-family:Calibri,sans-serif">avlat</i>, and use <i style="font-family:Calibri,sans-serif">cos(avlat)</i> to scale the longitudinal differences,<br>
then use the Euclidean formula.<u style="font-family:Calibri,sans-serif"></u><u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u style="font-family:Calibri,sans-serif"></u> <u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Regards,<u style="font-family:Calibri,sans-serif"></u><u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)">Mike<u style="font-family:Calibri,sans-serif"></u><u style="font-family:Calibri,sans-serif"></u></span></p></div></div><div lang="EN-US" link="blue" vlink="purple"><div class="m_2757397243505280229WordSection1">
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u style="font-family:Calibri,sans-serif"></u> <u style="font-family:Calibri,sans-serif"></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:Calibri,sans-serif;color:rgb(31,73,125)"><u style="font-family:Calibri,sans-serif"></u> <u style="font-family:Calibri,sans-serif"></u></span></p>
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<p class="MsoNormal"><b><span style="font-size:10pt;font-family:Tahoma,sans-serif">From:</span></b><span style="font-size:10pt;font-family:Tahoma,sans-serif"> erlang-questions [mailto:<a href="mailto:erlang-questions-bounces@erlang.org" target="_blank" style="font-family:Tahoma,sans-serif">erlang-questions-bounces@erlang.org</a>]
<b style="font-family:Tahoma,sans-serif">On Behalf Of </b>Ivan Uemlianin<br>
<b style="font-family:Tahoma,sans-serif">Sent:</b> Thursday, November 26, 2020 6:14 AM<br>
<b style="font-family:Tahoma,sans-serif">To:</b> Frank Muller; Erlang-Questions Questions<br>
<b style="font-family:Tahoma,sans-serif">Subject:</b> Re: Find nearest geographic coordinates<u style="font-family:Tahoma,sans-serif"></u><u style="font-family:Tahoma,sans-serif"></u></span></p>
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<p class="MsoNormal" style="margin-bottom:12pt">Ooh interesting. Well there's your answer, although if you're always using it for `distance(A, X) < distance(B, X)` you could probably simplify the arithmetic.<br>
<br>
Ivan<br>
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<p class="MsoNormal">On 25/11/2020 22:09, Frank Muller wrote:<u></u><u></u></p>
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<p class="MsoNormal">I’m new to GIS field, but this module states that Euclidian distance isn’t accurate compared to “Law of Haversines”:<u></u><u></u></p>
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<p class="MsoNormal"><a href="https://github.com/armon/teles/blob/master/src/teles_geo_query.erl#L87-L102" target="_blank">https://github.com/armon/teles/blob/master/src/teles_geo_query.erl#L87-L102</a><u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal">/Frank<u></u><u></u></p>
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<p class="MsoNormal">Wed 25 nov. 2020 à 22:45, Ivan Uemlianin <<a href="mailto:ivan@llaisdy.com" target="_blank">ivan@llaisdy.com</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal" style="margin-bottom:12pt">Hi Frank<br>
<br>
Do you want to sort the list by Euclidean distance from X? If so, could <br>
you use lists:sort/2?<br>
<br>
Ivan<br>
<br>
<br>
On 25/11/2020 21:38, Frank Muller wrote:<br>
> Hi guys,<br>
><br>
> I've a list of geographic coordinates:<br>
><br>
> L = [ {{<<"longitude">>,6.1457}, {<<"latitude">>,46.2022}},<br>
> {{<<"longitude">>,2.3387}, {<<"latitude">>,48.8582}},<br>
> ... ]<br>
><br>
> and a specific coordinate X = {{<<"longitude">>,-73.5848}, <br>
> {<<"latitude">>,45.4995}}.<br>
><br>
> Question: how can i find the nearest coordinates to X from L (sorted <br>
> from the nearest to the farest)?<br>
><br>
> /Frank<br>
<br>
-- <br>
============================================================<br>
Ivan A. Uemlianin PhD<br>
Llaisdy<br>
<br>
Ymchwil a Datblygu Technoleg Lleferydd<br>
Speech Technology Research and Development<br>
<br>
<a href="mailto:ivan@llaisdy.com" target="_blank">ivan@llaisdy.com</a><br>
@llaisdy<br>
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llaisdy.wordpress.com</a><br>
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www.linkedin.com/in/ivanuemlianin</a><br>
<br>
festina lente<br>
============================================================<u></u><u></u></p>
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<pre style="font-family:monospace">-- <u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace">============================================================<u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace">Ivan A. Uemlianin PhD<u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace">Llaisdy<u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace"><u style="font-family:monospace"></u> <u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace">Ymchwil a Datblygu Technoleg Lleferydd<u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace">Speech Technology Research and Development<u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace"><u style="font-family:monospace"></u> <u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace"> <a href="mailto:ivan@llaisdy.com" target="_blank" style="font-family:monospace">ivan@llaisdy.com</a><u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace"> @llaisdy<u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace"> <a href="http://llaisdy.wordpress.com" target="_blank" style="font-family:monospace">llaisdy.wordpress.com</a><u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace"> <a href="http://github.com/llaisdy" target="_blank" style="font-family:monospace">github.com/llaisdy</a><u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace"> <a href="http://www.linkedin.com/in/ivanuemlianin" target="_blank" style="font-family:monospace">www.linkedin.com/in/ivanuemlianin</a><u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace"><u style="font-family:monospace"></u> <u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace"> festina lente<u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
<pre style="font-family:monospace">============================================================<u style="font-family:monospace"></u><u style="font-family:monospace"></u></pre>
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