<div dir="ltr"><span style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">Dear DAL members,</span><br style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">at the recent IVOA Interop in Victoria it was pointed out</span><br style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">by Alberto</span><br style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><br style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><a href="http://wiki.ivoa.net/internal/IVOA/InterOpMayy2018DAL/ivoa_201805_micol_polygons.pdf" target="_blank" style="color:rgb(17,85,204);font-size:12.8px">http://wiki.ivoa.net/internal/<wbr>IVOA/InterOpMayy2018DAL/ivoa_<wbr>201805_micol_polygons.pdf</a><br style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><br style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">that not all the data providers follow the STC specification</span><br style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial;float:none;display:inline">about the winding direction of polygons stored in their</span><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial">archives.<br><br>STC states that &quot;The inside of the region is defined as <div>that part of coordinate space that is encircled by the </div><div>polygon in a counter-clockwise sense&quot;.<div><div></div></div></div><div>And this is to be considered when looking at the</div><div>celestial sphere from the inside.</div><div><br></div><div>The different behaviour of the polygons stored at </div><div>different sites creates an interoperability issue.</div><div><br></div><div>This email is a request on data providers to check</div><div>on their data and implementations (when dealing</div></div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial">with polygons) to solve the presented issue.</div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial">James also put together a python code snippet </div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial">implementing a simple test, it is available here:</div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="text-decoration-style:initial;text-decoration-color:initial"><span style="font-size:12.8px"><a href="https://gist.github.com/jd-au/45d1cdc0c6e2a7bc848a4be8f46c8958">https://gist.github.com/jd-au/45d1cdc0c6e2a7bc848a4be8f46c8958</a></span><br></div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial"><br></div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial">Thank you in advance!</div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial">Cheers,</div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial">       Marco &amp; James</div><div style="font-size:12.8px;text-decoration-style:initial;text-decoration-color:initial">      (your DAL chair &amp; vice)</div><br></div>