[Qgis-user] True North

[Springfield Harrison]

OK, thank you.  That formula is useful.

I assume that "North" for any projection will be grid North so that a 
line drawn at 0° while using a UTM projection will point to grid North 
if the drawing is re-projected using an un-projected CRS (where 0° is 
true North)?

I wonder if I have that correct?  I will check some of the other 
responses also.

Thanks very much…

Cheers . . . . . Spring Harrison


On 03-Apr-2018 02:15, Alexandre Neto wrote:
> Maybe something like this :
>
> https://gis.stackexchange.com/q/115531/6191
>
> Alexandre
>
> A ter, 3/04/2018, 10:11, Alexandre Neto <senhor.neto at gmail.com 
> <mailto:senhor.neto at gmail.com>> escreveu:
>
>     Ah sorry,
>
>     I got lost in translation. You are right, I was talking about the
>     magnetic north, not the geodetic one.
>
>     Meanwhile,  remembering that all UTM are Transverse Mercator, I
>     don't think there's a CRS that will solve you question.
>
>     I think you need to use some formula to convert the grid north
>     measures to true north according to the CRS, and the latitude and
>     longitude of the place.
>
>     Alexandre
>
>
>     A ter, 3/04/2018, 09:25, Springfield Harrison
>     <stellargps at gmail.com <mailto:stellargps at gmail.com>> escreveu:
>
>         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
>
>             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
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>
>     -- 
>     Alexandre Neto
>     ---------------------
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>
> -- 
> Alexandre Neto
> ---------------------
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