Find nearest geographic coordinates

[FRENCH Mike]

1. What is the overall extent of the points?

2. Do you need the exact answer?
   e.g. will there be many points close together and you have to get the correct one;
            can you assume a spherical Earth, not model the exact geoid shape (WGS84,etc.)

3. Does the region include the areas around the poles or crossing the 180 longitude ‘dateline’?

If (1) is ‘small’ or ‘a few 100 km’, and (2) and (3) are NO, then there are some simple methods …

If it is a localized region near the equator (e.g. within Singapore) you can use the Euclidean formula directly.

If it is a localized region, you can assume the ‘2D tangent plane projection’ Euclidean approximation.
Take the middle value for the latitude, avlat,  and use cos(avlat) to scale the longitudinal differences,
then use the Euclidean formula.

Regards,
Mike


From: erlang-questions [mailto:erlang-questions-bounces@REDACTED] On Behalf Of Ivan Uemlianin
Sent: Thursday, November 26, 2020 6:14 AM
To: Frank Muller; Erlang-Questions Questions
Subject: Re: Find nearest geographic coordinates

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.

Ivan

On 25/11/2020 22:09, Frank Muller wrote:
I’m new to GIS field, but this module states that Euclidian distance isn’t accurate compared to “Law of Haversines”:

https://github.com/armon/teles/blob/master/src/teles_geo_query.erl#L87-L102


/Frank

Wed 25 nov. 2020 à 22:45, Ivan Uemlianin <ivan@REDACTED<mailto:ivan@REDACTED>> wrote:
Hi Frank

Do you want to sort the list by Euclidean distance from X?  If so, could
you use lists:sort/2?

Ivan


On 25/11/2020 21:38, Frank Muller wrote:
> Hi guys,
>
> I've a list of geographic coordinates:
>
> L = [ {{<<"longitude">>,6.1457}, {<<"latitude">>,46.2022}},
>       {{<<"longitude">>,2.3387}, {<<"latitude">>,48.8582}},
>       ... ]
>
> and a specific coordinate X = {{<<"longitude">>,-73.5848},
> {<<"latitude">>,45.4995}}.
>
> Question: how can i find the nearest coordinates to X from L (sorted
> from the nearest to the farest)?
>
> /Frank

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Ivan A. Uemlianin PhD
Llaisdy

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Speech Technology Research and Development

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                         festina lente
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--

============================================================

Ivan A. Uemlianin PhD

Llaisdy



Ymchwil a Datblygu Technoleg Lleferydd

Speech Technology Research and Development



                    ivan@REDACTED<mailto:ivan@REDACTED>

                        @llaisdy

                         llaisdy.wordpress.com

              github.com/llaisdy

                     www.linkedin.com/in/ivanuemlianin<http://www.linkedin.com/in/ivanuemlianin>



                        festina lente

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