[Qgis-user] representation of angles in QGIS - recalculation to arithmetic values

[Richard Greenwood]

g = (450-m) - int((450-m) / 360) * 360
where m = mathematical angle (0 east, anti-clockwise)
and g = geographic angle (0 north, clockwise)

On Mon, Dec 6, 2021 at 11:02 AM <geo.guide at web.de> wrote:

> Dear colleagues on the QGIS user list,
>
> have an urgent problem with the representation of arrows with a data
> defined angle in QGIS.
>
> Up to now the free GIS world lived with angles assuming north being 0,
> east being 90 degrees and so on clockwise until reaching north again (which
> might be 360 degrees as well). At least QGIS and many other GIS programs
> work such a way.
>
> But: Now I have encountered a new version - probably created in the ESRI
> world, perhaps for harassment or to create a distinctive new feature. This
> is called an arithmetic angle, having East for 0 degree, North for 90
> degrees and so on counter-clockwise !
> Actually I it's somehow hard to preserve my humour for this invention.
>
> Is there a simple possibility to recalculate the "normal" northed angles
> to the "arithmetic" easted angles ? It's not that easy, because the
> rotation is counter-clockwise.
>
> Should very urgently prepare some maps with flow arrows in QGIS which
> normally assumes northed (geographical) angles .... The values got
> automatically exported from a simulation software with the arithmetic angle
> system, can't change that.  By the way this is meanwhile also demanded by
> south german agency as an output specification.
>
> Has somebody a clue how to solve such a problem in QGIS or how to
> recalculate from one to the other system ? Have about 5000 values, so
> little chance to get this done manually. At least not in time.
>
> Thanks a lot for a soon feed back,
> Christine
>
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-- 
Richard W. Greenwood
www.greenwoodmap.com
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