<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8">
</head>
<body text="#660000" bgcolor="#FFFFFF">
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">Hi
people, <br>
</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">I am
having some problems with the rHealPix projection and maybe
you can help me.</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">In
(0,0)-rHealPix (i.e. north_square = south_square = 0), I
understand that the top left corner is (-PI, 3*PI/4).<br>
</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">However
trying to project that point to lon-lat WGS84 fails.</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">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).<br>
</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">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: <br>
</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">proj
+proj=rhealpix -f '%.4f' -I +lon_0=0 +a=1 +ellps=WGS84
+north_square=0 +south_square=0 -E <br>
</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">and
some of the results I get are these:</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">-3.14
2.35<br>
-3.14 2.35 * *<br>
-3.13 2.34<br>
-3.13 2.34 90.3176 42.4654<br>
-3.138 2.348<br>
-3.138 2.348 90.3144 41.9431<br>
-3.139 2.349<br>
-3.139 2.349 * *<br>
</font></font></p>
<p><br>
<font size="+1"><font face="Helvetica, Arial, sans-serif">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).</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">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).<br>
</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">Am I
doing something wrong, or is this a problem with rHeallPix in
Proj.4?</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif">Thanks
in advance!</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif"> Rubén<br>
</font></font></p>
<p><font size="+1"><font face="Helvetica, Arial, sans-serif"></font></font><br>
</p>
<div class="moz-signature">-- <br>
<div>
<meta http-equiv="Content-Type" content="text/html;
charset=utf-8">
<p style="margin:0px; font-size:11pt; font-family:Arial,
sans-serif; color:#223D71;"> Dr. Rubén Béjar<br>
<a style="margin:0px; font-size:11pt; font-family:Arial,
sans-serif; color:#223D71; text-decoration: none"
href="https://www.unizar.es"><b>Universidad</b> Zaragoza</a><br>
<a style="margin:0px; font-size:10pt; font-family:Arial,
sans-serif; color:#223D71; text-decoration: none"
href="https://www.iaaa.es/"><span style="font-style:italic"
lang="en">Advanced Information Systems Laboratory</span></a><br>
<a style="margin:0px; font-size:10pt; font-family:Arial,
sans-serif; color:#223D71; text-decoration: none"
href="http://i3a.unizar.es/"><span style="font-style:italic"
lang="en">Aragon Institute of Engineering Research</span></a><br>
<br>
<a style="margin:0px; font-size:10pt; font-family:Arial,
sans-serif; color:#223D71; text-decoration: none"
href="mailto:rbejar@unizar.es">rbejar@unizar.es</a> <a
style="margin:0px; font-size:10pt; font-family:Arial,
sans-serif; color:#223D71; text-decoration: none"
href="https://twitter.com/rubejar">(@rubejar in Twitter)</a><br>
<a style="margin:0px; font-size:10pt; font-family:Arial,
sans-serif; color:#B04F00; text-decoration: none"
href="https://www.rubenbejar.com"><b>rubenbejar</b>.com</a>
<br>
----<br>
</p>
<p style="margin:0px; font-size:10pt; font-family:Arial,
sans-serif; color:black;">Departamento de Informática e
Ingeniería de Sistemas</p>
<p style="margin:0px; font-size:10pt; font-family:Arial,
sans-serif; color:black;">María de Luna 1 / 50018 / Zaragoza <span
style="font-style:italic" lang="en">(Spain)</span><br>
Tlf: +34 876 555534 / Fax: +34 976 761914 </p>
</div>
</div>
</body>
</html>