STC-1_33-Erratum-2 < IVOA

---+ [[STC]]-1.33 Erratum 2:

Author: DM WG

Date last changed: 2018-11-18

Date accepted:2019-04-16
---++ Rationale

This erratum is to correct an error reported at the IVOA interop in Victoria, BC: May 2018

   * <a target="_blank" href="http://wiki.ivoa.net/internal/IVOA/InterOpMayy2018DAL/ivoa_201805_micol_polygons.pdf">POLYGON with different orientations issue</a> cite:
<div title="Page 6">

<em>Section 4.5.1.4 (pg 30-31: Region.Polygon) states:</em><em>"The inside of the region is defined as that part of coordinate space that is encircled by the polygon in a counter-clockwise sense. What this means is that, in a plane, if A &gt; 0, the &ldquo;inside&rdquo; of the polygon is included; if A &lt; 0, the &ldquo;outside&rdquo; is selected. On a sphere with a left-handed (celestial) coordinate system, if A &gt; 0, one has identified the inside of the polygon; *if A &lt; 0, one used the &ldquo;outside&rdquo; angles of the polygon and the area* *is really 4&pi; &minus; A* <br /></em><em>The incorrect text is shown in bold text:</em><em><br />This is also wrong because if A &lt; 0 then 4*pi &ndash; A is &gt; 4*pi, and that cannot be.</em><em><br />The correct text is:<br /></em><em>"<strong>if A &lt; 0, one used the &ldquo;outside&rdquo; angles of the polygon and the area is really 4&pi; + A</strong> </em>
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---++ Erratum Content
<div title="Page 6">
---++++ Original Wording
   * Section 4.5.1.4 (pg 30-31: Region.Polygon) :<span style="background-color: transparent;"><strong> if A &lt; 0, one used the &ldquo;outside&rdquo; angles of the polygon and the area</strong> </span><span style="background-color: transparent;"> *is really 4&pi; &minus; A* . </span>
<div title="Page 7">
---++++ New Wording
   * Section 4.5.1.4 (pg 30-31: Region.Polygon) :<strong><span style="background-color: transparent;"> if A &lt; 0, one used the &ldquo;outside&rdquo; angles of the polygon and the area is really 4&pi; + A </span></strong>
</div> </div>
---++ Impact Assessment
   * Software using the wrong formula must be updated
---++ Notes

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This topic: IVOA > WebHome > IvoaDataModel > STC > STC-1_33-Errata > STC-1_33-Erratum-2
Topic revision: r4 - 2019-05-08 - MarkCresitelloDittmar