<div dir="ltr"><div>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:<br><br><span style="font-family:monospace,monospace">$ echo 12 55 | proj -V +proj=utm +zone=32 +ellps=GRS80</span><br><br><span style="font-family:monospace,monospace">#Universal Transverse Mercator (UTM)<br># Cyl, Sph<br># zone= south<br># +proj=utm +zone=32 +ellps=GRS80<br>#--- following specified but NOT used<br># +ellps=WGS84<br>#Final Earth figure: ellipsoid<br># Major axis (a): 6378137.000<br># 1/flattening: 298.257222<br># squared eccentricity: 0.006694380023<br> <br>Longitude: 12dE [ 12 ]<br>Latitude: 55dN [ 55 ]<br>Easting (x): 691875.63<br>Northing (y): 6098907.83<br>Meridian scale (h) : 1.00005168 ( 0.005168 % error )<br>Parallel scale (k) : 1.00005168 ( 0.005168 % error )<br>Areal scale (s): 1.00010336 ( 0.01034 % error )<br>Angular distortion (w): 0.000<br>Meridian/Parallel angle: 90.00000<br>Convergence : 2d27'29.52" [ 2.45819987 ]<br>Max-min (Tissot axis a-b) scale error: 1.00005 1.00005<br><br></span></div><span style="font-family:monospace,monospace"><font face="arial,helvetica,sans-serif">Where the convergence (here 2.45819987)</font></span><span style="font-family:monospace,monospace"><font face="arial,helvetica,sans-serif"><span style="font-family:monospace,monospace"><font face="arial,helvetica,sans-serif"> is what you need</font></span>, if I understand your question correctly.<br><br>See the reply by Martin F over at <a href="https://gis.stackexchange.com/questions/61743/applying-proper-conversion-from-true-to-grid-bearing">https://gis.stackexchange.com/questions/61743/applying-proper-conversion-from-true-to-grid-bearing</a> for instructions of how to apply this.</font><br></span><div><div><br></div><div><br></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">2018-01-30 12:42 GMT+01:00 Chen Barnoy <span dir="ltr"><<a href="mailto:jicrbuh1@gmail.com" target="_blank">jicrbuh1@gmail.com</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="rtl"><div dir="ltr">Hi,</div><div dir="ltr"><br></div><div dir="ltr">Is there a way to convert between grid north, true north and magnetic north in Proj4 or another library?</div><div dir="ltr"><br></div><div dir="ltr">Cheers,</div><div dir="ltr">Chen</div></div>
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