<div dir="ltr"><div>(this time responding to list)<br><br></div><div>Either are valid ways to define polygons and I asked about this
awhile back (probably ~Madrid interop). The STC definition requires the
vertex sequence to be counter-clockwise while the other doesn't care but
then you need to compute the winding direction. <br><br></div>So, this
was intentional (several geometry libraries I have checked or used do it
this way). Whichever was chosen, someone has to do some work: either
computing the winding direction or converting polygons computed by some
library to the standard winding direction... <br><br>I assume "complicates our implementation" means "have to compute the winding direction and maybe reverse vertex order"?<div class=""><div id=":2i7" class="" tabindex="0"><img class="" src="https://ssl.gstatic.com/ui/v1/icons/mail/images/cleardot.gif"></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Feb 10, 2016 at 1:01 PM, Patrick Dowler <span dir="ltr"><<a href="mailto:pdowler.cadc@gmail.com" target="_blank">pdowler.cadc@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Either are valid ways to define polygons and I asked about this awhile back (probably ~Madrid interop). The STC definition requires the vertex sequence to be counter-clockwise while the other doesn't care but then you need to compute the winding direction. <br><br></div>So, this was intentional (several geometry libraries I have checked or used do it this way). Whichever was chosen, someone has to do some work: either computing the winding direction or converting polygons computed by some library to the standard winding direction... <br><br>I assume "complicates our implementation" means "have to compute the winding direction and maybe reverse vertex order"?<br><br></div><div class="gmail_extra"><div><div class="h5"><br><div class="gmail_quote">On Wed, Feb 10, 2016 at 12:09 AM, Alex Szalay <span dir="ltr"><<a href="mailto:szalay@jhu.edu" target="_blank">szalay@jhu.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">STC is mathematically correct and tested carefully. If SIA2 disagrees, it is most likely incorrect.<br>
<span><font color="#888888"><br>
--Alex<br>
</font></span><div><div><br>
-----Original Message-----<br>
From: <a href="mailto:dal-bounces@ivoa.net" target="_blank">dal-bounces@ivoa.net</a> [mailto:<a href="mailto:dal-bounces@ivoa.net" target="_blank">dal-bounces@ivoa.net</a>] On Behalf Of Walter Landry<br>
Sent: Wednesday, February 10, 2016 3:01 AM<br>
To: <a href="mailto:dal@ivoa.net" target="_blank">dal@ivoa.net</a><br>
Subject: Difference in polygon's between SIA2 and ADQL<br>
<br>
Hello Everyone,<br>
<br>
Reading the description of polygons in ADQL, it links to the description in STC.<br>
<br>
<a href="http://www.ivoa.net/Documents/cover/STC-20071030.html" rel="noreferrer" target="_blank">http://www.ivoa.net/Documents/cover/STC-20071030.html</a><br>
<br>
That defines a polygon as the points to the left of the edges. In contrast, in SIA2, a polygon is defined as the region with smaller area. Was that inconsistency intentional? It complicates our implementation.<br>
<br>
Thanks,<br>
Walter Landry<br>
</div></div></blockquote></div><br><br clear="all"><br></div></div><span class="HOEnZb"><font color="#888888">-- <br><div><div dir="ltr"><div><div>Patrick Dowler<br></div>Canadian Astronomy Data Centre<br></div>Victoria, BC, Canada<br></div></div>
</font></span></div>
</blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature"><div dir="ltr"><div><div>Patrick Dowler<br></div>Canadian Astronomy Data Centre<br></div>Victoria, BC, Canada<br></div></div>
</div>