[Qgis-user] True North

[Alexandre Neto]

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>
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> 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>
>> 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://gisunchained.wordpress.com
>>
> --
Alexandre Neto
---------------------
@AlexNetoGeo
http://sigsemgrilhetas.wordpress.com
http://gisunchained.wordpress.com
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