[Qgis-user] True North

Wed Apr 4 23:32:37 PDT 2018

Hi,

Is this what you need?

http://plugins.qgis.org/plugins/AzimuthDistanceCalculator/version/2.0/

Just stumbled on the description of this plugin and it mention that it can
calculate the convergence for UTM.

Hope it helps.

Alexandre Neto

A qua, 4/04/2018, 22:56, Springfield Harrison <stellargps at gmail.com>
escreveu:

> hello Kristian,
>
> Thanks again for your help, I was partially successful. The second grid,
> the custom Mercator one that you described is not happy in the print
> composer. It does not persist but seems to revert back to the UTM grid with
> the word change on the CRS button.
>
> Not sure what that is all about but my main requirement is to be able to
> draw lines at specific angles with reference to true north. They will then
> be re -projected correctly based on the display projection. Unfortunately,
> the advanced digitizing tool does not work with Geographic projections, IE
> un projected Maps.
>
> If I can get lines that are guaranteed to be related to Geographic
> bearings, I could let the projection quirks sort themselves out on their
> own.
>
> If you have any thoughts on this I would be most appreciative...
>
> Cheers . . . . .   Spring
> Samsung Tab 4
> On Apr 4, 2018 9:41 AM, "Springfield Harrison" <stellargps at gmail.com>
> wrote:
>
>> Okay, great. That is very helpful, I will work in the map composer. I
>> know what you are referring to there. Thanks again...
>>
>> Cheers . . . . .   Spring
>> Samsung Tab 4
>> On Apr 4, 2018 9:36 AM, "Kristian Evers" <kreve at sdfe.dk> wrote:
>>
>>> I made it within the Layout Composer/Editor (what it’s called in QGIS3
>>> escapes me now – it used to be Map Composer in 2.x). That was the simplest
>>> way to achieve it quickly I found. You have the possibility to add more
>>> than one graticule and you can also change the CRS of the graticule. That
>>> is what I did. One was kept in UTM, the other used my custom Mercator CRS.
>>>
>>>
>>>
>>> This is just one way of doing it. There many ways to achieve the same
>>> thing, but this should outline the general idea at least.
>>>
>>>
>>>
>>> My last post was not let through to the mailing list, so here’s a copy
>>> of the image I attached in the previous mail. Should anyone be interested…
>>>
>>>
>>>
>>> /Kristian
>>>
>>>
>>>
>>>
>>>
>>> *Fra:* Springfield Harrison [mailto:stellargps at gmail.com]
>>> *Sendt:* 4. april 2018 16:19
>>> *Til:* Kristian Evers <kreve at sdfe.dk>
>>> *Cc:* qgis-user <qgis-user at lists.osgeo.org>
>>> *Emne:* Re: SV: [Qgis-user] True North
>>>
>>>
>>>
>>> Right, this looks promising.
>>>
>>> I have been changing projections and then enabling the grid decoration
>>> which is always oriented straight up regardless of the projection.
>>>
>>> I assume that you were inserting your grids as a vector feature using a
>>> drawing tool?
>>>
>>> What was the CRS of the grid layer? I have been changing the project
>>> projection with OTF on. Maybe I should be adjusting the projection of the
>>> layer in question?
>>>
>>> Thanks again . . .
>>>
>>> Cheers . . . . .   Spring
>>> Samsung Tab 4
>>>
>>> On Apr 4, 2018 5:23 AM, "Kristian Evers" <kreve at sdfe.dk> wrote:
>>>
>>> I had a quick go at it after I wrote the email. What I did was to first
>>> create a custom projection with the proj-string “+proj=merc”. Then I opened
>>> the layout editor, inserted my map and added to sets of grid lines to the
>>> map. One of them was left with the original CRS (the UTM one) and for the
>>> other I used my custom CRS. This immediately gave me two grids, one where
>>> the meridians is oriented at the grid north (black in the attached image)
>>> and one oriented at true north (red in the attached image).
>>>
>>>
>>>
>>> /Kristian
>>>
>>>
>>>
>>> *Fra:* Springfield Harrison [mailto:stellargps at gmail.com]
>>> *Sendt:* 3. april 2018 22:52
>>> *Til:* qgis-user at lists.osgeo.org; Kristian Evers <kreve at sdfe.dk>
>>> *Emne:* Re: [Qgis-user] True North
>>>
>>>
>>>
>>> OK, that sounds like the solution I'm looking for.
>>>
>>> It sounds like the answer is to draw the lines in one projection and
>>> then transform it to the other, depending upon which orientation is desired
>>> for those lines.
>>>
>>> I hope I have this correct…
>>>
>>> Cheers . . . . . Springfield Harrison
>>>
>>>
>>>
>>> On 03-Apr-2018 02:46, Kristian Evers wrote:
>>>
>>> You can use the Mercator projection to digitize true north lines. It is
>>> conformal and thus preserves angles. The meridian convergence is 0 (that
>>> is, true north == grid north) all over the map. If you then transform those
>>> lines to your chosen CRS you should have a set of lines pointing towards
>>> true north instead of grid north.
>>>
>>>
>>>
>>> /Kristian
>>>
>>>
>>>
>>> *Fra:* Qgis-user [mailto:qgis-user-bounces at lists.osgeo.org
>>> <qgis-user-bounces at lists.osgeo.org>] *På vegne af *Alexandre Neto
>>> *Sendt:* 3. april 2018 11:15
>>> *Til:* Springfield Harrison <stellargps at gmail.com>
>>> <stellargps at gmail.com>
>>> *Cc:* qgis-user <qgis-user at lists.osgeo.org> <qgis-user at lists.osgeo.org>
>>> *Emne:* Re: [Qgis-user] True North
>>>
>>>
>>>
>>> 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>
>>> 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>
>>> 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
>>>
>>> --
>>>
>>> Alexandre Neto
>>>
>>> ---------------------
>>>
>>> @AlexNetoGeo
>>>
>>> http://sigsemgrilhetas.wordpress.com
>>>
>>> http://gisunchained.wordpress.com
>>>
>>>
>>>
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-- 
Alexandre Neto
---------------------
@AlexNetoGeo
http://sigsemgrilhetas.wordpress.com
http://gisunchained.wordpress.com
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