[Proj] A rHealPix bug or I am misunderstanding something

[Thomas Knudsen]

Rubén,

first, I recommend not mixing "minus style" general options with "plus
style" projection definitions. It works for proj and cs2cs, but will not
for the next generation tool, cct, so I suggest saying:

proj -EIf '%.4f' +proj=rhealpix +lon_0=0 +a=1 +ellps=WGS84 +north_square=0
+south_square=0

second: I can replicate your results, but...

third: I have no idea what it means, and cannot help - any rHealpix users
here? Please speak up!

/thomas

Den tir. 9. okt. 2018 kl. 10.19 skrev Rubén Béjar <rbejar at unizar.es>:

> Hi people,
>
> I am having some problems with the rHealPix projection and maybe you can
> help me.
>
> In (0,0)-rHealPix (i.e. north_square = south_square = 0), I understand
> that the top left corner is (-PI, 3*PI/4).
>
> However trying to project that point to lon-lat WGS84 fails.
>
> I am running proj 5.2.0 (September 15th, 2018) in a terminal in Ubuntu
> 18.04 (I have compiled it from sources, I am not using the older version
> from the repositories).
>
> I assumed that it could be due to some tolerances/epsilon issues. However
> it does not seem to be so. I have tried with this command:
>
> proj +proj=rhealpix -f '%.4f' -I +lon_0=0 +a=1 +ellps=WGS84
> +north_square=0 +south_square=0 -E
>
> and some of the results I get are these:
>
> -3.14 2.35
> -3.14 2.35      *       *
> -3.13 2.34
> -3.13 2.34      90.3176 42.4654
> -3.138 2.348
> -3.138 2.348    90.3144 41.9431
> -3.139 2.349
> -3.139 2.349    *       *
>
>
> So even after "pushing" the top left corner to the right (from -PI to
> -3.14, big difference) and down (from 3*PI/4 to 2.35, again big difference)
> I still don't get a conversion. The closest to the "real" point that seems
> to work is around (-3.138, 2.349) which is far from that corner (much
> further than a tolerance).
>
> This corner is a simple, easily reproducible case. I am having similar
> problems close to the edges of the N square (and possibly close to some of
> the edges of other squares too).
>
> Am I doing something wrong, or is this a problem with rHeallPix in Proj.4?
>
> Thanks in advance!
>
>   Rubén
>
>
> --
>
> Dr. Rubén Béjar
> *Universidad* Zaragoza <https://www.unizar.es>
> Advanced Information Systems Laboratory <https://www.iaaa.es/>
> Aragon Institute of Engineering Research <http://i3a.unizar.es/>
>
> rbejar at unizar.es  (@rubejar in Twitter) <https://twitter.com/rubejar>
> *rubenbejar*.com <https://www.rubenbejar.com>
> ----
>
> Departamento de Informática e Ingeniería de Sistemas
>
> María de Luna 1 / 50018 / Zaragoza (Spain)
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