Converting between true north, grid north, and magnetic north

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Converting between true north, grid north, and magnetic north

Chen Barnoy
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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Re: Converting between true north, grid north, and magnetic north

Thomas Knudsen
The magnetic north varies from location to location is not easy to handle, but you can get deviation from grid north using the -V option to proj:

$  echo 12 55 | proj -V +proj=utm +zone=32 +ellps=GRS80

#Universal Transverse Mercator (UTM)
#    Cyl, Sph
#    zone= south
# +proj=utm +zone=32 +ellps=GRS80
#--- following specified but NOT used
# +ellps=WGS84
#Final Earth figure: ellipsoid
#  Major axis (a): 6378137.000
#  1/flattening: 298.257222
#  squared eccentricity: 0.006694380023
 
Longitude: 12dE [ 12 ]
Latitude:  55dN [ 55 ]
Easting (x):   691875.63
Northing (y):  6098907.83
Meridian scale (h) : 1.00005168  ( 0.005168 % error )
Parallel scale (k) : 1.00005168  ( 0.005168 % error )
Areal scale (s):     1.00010336  ( 0.01034 % error )
Angular distortion (w): 0.000
Meridian/Parallel angle: 90.00000
Convergence : 2d27'29.52" [ 2.45819987 ]
Max-min (Tissot axis a-b) scale error: 1.00005 1.00005

Where the convergence (here 2.45819987) is what you need, if I understand your question correctly.

See the reply by Martin F over at https://gis.stackexchange.com/questions/61743/applying-proper-conversion-from-true-to-grid-bearing for instructions of how to apply this.




2018-01-30 12:42 GMT+01:00 Chen Barnoy <[hidden email]>:
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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Re: Converting between true north, grid north, and magnetic north

Clifford J Mugnier
The Geodesy & Geophysics web page at the NGA.mil site has the Isogonic (magnetism) model that can be downloaded.

Sent from Cliff Mugnier's iPhone

On Jan 30, 2018, at 6:37 AM, Thomas Knudsen <[hidden email]> wrote:

The magnetic north varies from location to location is not easy to handle, but you can get deviation from grid north using the -V option to proj:

$  echo 12 55 | proj -V +proj=utm +zone=32 +ellps=GRS80

#Universal Transverse Mercator (UTM)
#    Cyl, Sph
#    zone= south
# +proj=utm +zone=32 +ellps=GRS80
#--- following specified but NOT used
# +ellps=WGS84
#Final Earth figure: ellipsoid
#  Major axis (a): 6378137.000
#  1/flattening: 298.257222
#  squared eccentricity: 0.006694380023
 
Longitude: 12dE [ 12 ]
Latitude:  55dN [ 55 ]
Easting (x):   691875.63
Northing (y):  6098907.83
Meridian scale (h) : 1.00005168  ( 0.005168 % error )
Parallel scale (k) : 1.00005168  ( 0.005168 % error )
Areal scale (s):     1.00010336  ( 0.01034 % error )
Angular distortion (w): 0.000
Meridian/Parallel angle: 90.00000
Convergence : 2d27'29.52" [ 2.45819987 ]
Max-min (Tissot axis a-b) scale error: 1.00005 1.00005

Where the convergence (here 2.45819987) is what you need, if I understand your question correctly.

See the reply by Martin F over at https://gis.stackexchange.com/questions/61743/applying-proper-conversion-from-true-to-grid-bearing for instructions of how to apply this.




2018-01-30 12:42 GMT+01:00 Chen Barnoy <[hidden email]>:
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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Re: Converting between true north, grid north, and magnetic north

Charles Karney
In reply to this post by Chen Barnoy
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
>
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
>
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Re: Converting between true north, grid north, and magnetic north

Kurt Schwehr-2
Be aware that the magnetic field is time varying.  It can change pretty quickly near the magnetic poles.

Yet another source... igrf.py


On Tue, Jan 30, 2018 at 7:03 AM, Charles Karney <[hidden email]> wrote:
GeographicLib https://geographiclib.sourceforge.io provides access to
several magnetic models via the MagneticField utility.  E.g.,

   echo <a href="tel:42.363%20-71.006" value="+14236371006">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
>
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
>
_______________________________________________
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[hidden email]
http://lists.maptools.org/mailman/listinfo/proj



--

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Re: 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 <[hidden email]> wrote:
Be aware that the magnetic field is time varying.  It can change pretty quickly near the magnetic poles.

Yet another source... igrf.py


On Tue, Jan 30, 2018 at 7:03 AM, Charles Karney <[hidden email]> wrote:
GeographicLib https://geographiclib.sourceforge.io provides access to
several magnetic models via the MagneticField utility.  E.g.,

   echo <a href="tel:42.363%20-71.006" value="+14236371006" target="_blank">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
>
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
>
_______________________________________________
Proj mailing list
[hidden email]
http://lists.maptools.org/mailman/listinfo/proj



--

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Re: Converting between true north, grid north, and magnetic north

Chen Barnoy
In reply to this post by Kurt Schwehr-2
Thanks!

And is there a similar library to convert between grid\UTM north to true north?

2018-01-30 23:59 GMT+02:00 Kurt Schwehr <[hidden email]>:
Be aware that the magnetic field is time varying.  It can change pretty quickly near the magnetic poles.

Yet another source... igrf.py


On Tue, Jan 30, 2018 at 7:03 AM, Charles Karney <[hidden email]> wrote:
GeographicLib https://geographiclib.sourceforge.io provides access to
several magnetic models via the MagneticField utility.  E.g.,

   echo <a href="tel:42.363%20-71.006" value="+14236371006" target="_blank">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
>
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
>
_______________________________________________
Proj mailing list
[hidden email]
http://lists.maptools.org/mailman/listinfo/proj



--

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Re: Converting between true north, grid north, and magnetic north

Thomas Knudsen
libproj, the library behind proj, provides what you need, but you'll have to do some coding yourself. If you're using the new API in te brand new PROJ 5.0.0 release candidate, just announced, use the proj_factors(PJ, LP)  function - the convergence is in the PJ_FACTORS.meridian_convergence element. In the old API, use pj_factors, and get what you need from the struct FACTORS.conv element.

For smaller amounts of data, you can use proj to provide what you need, as outlined in my previous reply (which actually used UTM as example).

/thomas

 

2018-02-04 13:08 GMT+01:00 Chen Barnoy <[hidden email]>:
Thanks!

And is there a similar library to convert between grid\UTM north to true north?

2018-01-30 23:59 GMT+02:00 Kurt Schwehr <[hidden email]>:
Be aware that the magnetic field is time varying.  It can change pretty quickly near the magnetic poles.

Yet another source... igrf.py


On Tue, Jan 30, 2018 at 7:03 AM, Charles Karney <[hidden email]> wrote:
GeographicLib https://geographiclib.sourceforge.io provides access to
several magnetic models via the MagneticField utility.  E.g.,

   echo <a href="tel:42.363%20-71.006" value="+14236371006" target="_blank">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
>
>
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
>
_______________________________________________
Proj mailing list
[hidden email]
http://lists.maptools.org/mailman/listinfo/proj



--

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Re: Converting between true north, grid north, and magnetic north

karney
In reply to this post by Chen Barnoy
You can also use GeographicLib to compute the meridian convergence (the
bearing of grid north measured clockwise from true north) for the UTM
system.  Continuing with the Boston Logan Airport example:

     echo 42.363 -71.006 | GeoConvert -u => 19n 334812 4692030

     echo 42.363 -71.006 | GeoConvert -c => -1.35200 0.9999357

The first command gives you the UTM coordinates and the second the
meridian convergence and scale.

On 02/04/2018 07:08 AM, Chen Barnoy wrote:

> Thanks!
>
> And is there a similar library to convert between grid\UTM north to true
> north?
>
> 2018-01-30 23:59 GMT+02:00 Kurt Schwehr <[hidden email]
> <mailto:[hidden email]>>:
>
>     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
>     <https://earthref.org/PmagPy/cookbook/#x1-1190005.2.54>
>
>
> On Tue, Jan 30, 2018 at 7:03 AM, Charles Karney <[hidden email]
> <mailto:[hidden email]>> wrote:
>
>     GeographicLib https://geographiclib.sourceforge.io
>     <https://geographiclib.sourceforge.io> provides access to
>     several magnetic models via the MagneticField utility.  E.g.,
>
>         echo 42.363 -71.006 <tel:42.363%20-71.006> | 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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