[Qgis-user] Astronomical map

[Lester Anderson]

Quick update. Managed to fix the annotations using an expression in layout:

CASE

WHEN  @grid_number < 0 AND  @grid_axis ='x'
THEN (@grid_number  /-15)

WHEN  @grid_number = 0
THEN  @grid_number = 24

WHEN  @grid_number > 0 AND  @grid_axis ='x'
THEN  (360 - @grid_number)/15

WHEN  @grid_number > 0 AND @grid_axis ='y'
THEN  @grid_number

WHEN  @grid_number < 0 AND @grid_axis ='y'
THEN  @grid_number

END

Based on the east-west being +/- 180 degrees, so we have O (24) hours as
the central meridian. Annotations applied to a 15 degree longitude
graticule.



On Tue, 14 Jun 2022 at 07:20, Lester Anderson <arctica1963 at gmail.com> wrote:

> Hello all,
>
> I am interested in how one can generate an astronomical map based on Right
> Ascension (RA) and Declination (Dec), without converting RA to degrees and
> reversing (-15 * RA).
>
> There is the affine transform tool which can be used to scale X and flip,
> but this then generates the 0-360 degree scale. The main issue is that the
> IAU standard is for the RA to start at 24 and run east to 0!
>
> Any ideas would be most welcome.
>
> Lester
>
>
>
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