[Proj] A rHealPix bug or I am misunderstanding something
rbejar at unizar.es
Tue Oct 9 03:16:36 EST 2018
I am having some problems with the rHealPix projection and maybe you can
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 * *
-3.13 2.34 90.3176 42.4654
-3.138 2.348 90.3144 41.9431
-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!
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 <mailto:rbejar at unizar.es> (@rubejar in Twitter)
Departamento de Informática e Ingeniería de Sistemas
María de Luna 1 / 50018 / Zaragoza (Spain)
Tlf: +34 876 555534 / Fax: +34 976 761914
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