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

[J Luis]

Or GMT that even provides an estimate of daily variation.

https://gmt.soest.hawaii.edu/doc/5.4.3/supplements/mgd77/mgd77magref.html

On Tue, Jan 30, 2018 at 9:59 PM, Kurt Schwehr <schwehr at gmail.com> wrote:

> Be aware that the magnetic field is time varying.  It can change pretty
> quickly near the magnetic poles.
>
> Yet another source... igrf.py
>
> https://earthref.org/PmagPy/cookbook/#x1-1190005.2.54
>
> On Tue, Jan 30, 2018 at 7:03 AM, Charles Karney <charles.karney at sri.com>
> wrote:
>
>> 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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>
>
>
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