[Proj] Converting between true north, grid north, and magnetic north

[Charles Karney]

GeographicLib https://geographiclib.sourceforge.io provides access to
several magnetic models via the MagneticField utility.  E.g.,

   echo 42.363 -71.006 | MagneticField -t now

=>

   -14.67 67.08 20228.0 19569.1 -5121.1 47840.0 51940.7

The first number is the current magnetic declination at Boston Logan
Airport using the wmm2015 magnetic model.

The magnetic models need to be downloaded separately from the
GeographicLib library using

   geographiclib-get-magnetic

On 01/30/18 06:42, Chen Barnoy wrote:
> Hi,
> 
> Is there a way to convert between grid north, true north and magnetic 
> north in Proj4 or another library?
> 
> Cheers,
> Chen
> 
> 
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