[Qgis-user] True North

[Kirk Schmidt]

The central meridian in each utm zone is oriented directly at true north 
(Easting of 500,000 m).  The difference in angles when you move east of 
west of the meridian is referred to as convergence and the following 
link provides 2 formulas for calculating the convergence angles in utm 
projections.  A quick search on convergence calculators or methods 
should also provide some tools.

https://gis.stackexchange.com/questions/115531/how-to-calculate-grid-convergence-true-north-to-grid-north

Kirk


On 4/3/2018 5:25 AM, Springfield Harrison wrote:
>
> Alexandre,
>
> I believe that true north is actually a constant oriented towards the 
> North Pole, i e 90 degrees north latitude. Also where all meridians 
> converge in the northern hemisphere.
>
> The other North orientations are magnetic north and grid North and 
> these do vary as you suggested.
>
> I do need to use a UTM projection but need bearings to be in degrees 
> true north.
>
> Thanks Alexandre...
>
> Cheers . . . . .   Spring
> Samsung Tab 4
>
> On Apr 2, 2018 4:27 PM, "Alexandre Neto" <senhor.neto at gmail.com 
> <mailto:senhor.neto at gmail.com>> wrote:
>
>     AFAIK, true bearing differs in time and location because of
>     magnetic declination. So I don't think there is a such thing as a
>     CRS with true bearings.
>
>     Assuming you are working at regional level, find the magnetic
>     declination for that region and remove it from your observations.
>     Then draw the azimuth using the chosen CRS. I think 26910 will
>     work just fine.
>
>     If you are at a larger scale, then you may need to use different
>     magnetic declination values for each observation.
>
>     This may help:
>
>     https://www.ngdc.noaa.gov/geomag/declination.shtml
>     <https://www.ngdc.noaa.gov/geomag/declination.shtml>
>
>     Best Regards,
>
>     Alexandre Neto
>
>     A seg, 2/04/2018, 23:54, Springfield Harrison
>     <stellargps at gmail.com <mailto:stellargps at gmail.com>> escreveu:
>
>         Hello,
>
>         I am using CRS 26910, NAD83 / UTM zone 10N, and need to draw
>         lines at
>         exact true bearings.  The Advanced Digitizing Tool seems to do
>         this but
>         which CRS would I use to ensure that the bearing is True?
>
>         Thanks very much . . .
>
>
>         Cheers . . . . . Springfield Harrison
>
>
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>     -- 
>     Alexandre Neto
>     ---------------------
>     @AlexNetoGeo
>     http://sigsemgrilhetas.wordpress.com
>     <http://sigsemgrilhetas.wordpress.com>
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>
>
>
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-- 
Kirk Schmidt, MScF, BScF, RPF
General Manager
Nortek Resource Solutions Inc.
RR # 1
Thorburn, NS
B0K 1W0
Tel (902) 922.3607
Email: kirk at nortekresources.com
Web: www.nortekreources.com

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