# Find nearest geographic coordinates

Richard O'Keefe raoknz@REDACTED
Sat Nov 28 22:21:45 CET 2020

```It might be worth mentioning the
"Standards Of Fundamental Astronomy" (SOFA)
library:
https://www.iausofa.org/current_C.html

On Sun, 29 Nov 2020 at 08:10, Joa Gre <joagre@REDACTED> wrote:

> This might come in handy:
>
> %% https://en.m.wikipedia.org/wiki/Geographic_coordinate_conversion#From_geodetic_to_ECEF_coordinates
> %% https://en.m.wikipedia.org/wiki/Geodetic_datum#World_Geodetic_System_1984_(WGS_84)
>
> geodetic_to_ecef_coordinates(Latitude, Longitude, H) ->
>     CLatitude = math:cos(Latitude * ?RADIANS_PER_DEGREE),
>     SLatitude = math:sin(Latitude *  ?RADIANS_PER_DEGREE),
>     CLongitude = math:cos(Longitude * ?RADIANS_PER_DEGREE),
>     SLongitude = math:sin(Longitude  * ?RADIANS_PER_DEGREE),
>     %% Semi-major axis
>     A = 6378137.0,
>     A2 = math:pow(A, 2),
>     %% Semi-minor axis
>     B = 6356752.3142,
>     B2 = math:pow(B, 2),
>     %% Prime vertical radius of curvature
>     N = A2 / math:sqrt(
>                math:pow(CLatitude, 2) * A2 + math:pow(SLatitude, 2) * B2),
>     X = (N + H) * CLatitude * CLongitude,
>     Y = (N + H) * CLatitude * SLongitude,
>     Z  = (B2 / A2 * N + H) * SLatitude,
>     {X, Y, Z}.
>
>
> Den ons 25 nov. 2020 22:39Frank Muller <frank.muller.erl@REDACTED> skrev:
>
>> 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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