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Posted to issues@commons.apache.org by "Gilles Sadowski (Jira)" <ji...@apache.org> on 2021/05/21 23:49:00 UTC
[jira] [Resolved] (MATH-1507) Barycenter of a clockwise
SphericalPolygonsSet is incorrect.
[ https://issues.apache.org/jira/browse/MATH-1507?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Gilles Sadowski resolved MATH-1507.
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Resolution: Feedback Received
> Barycenter of a clockwise SphericalPolygonsSet is incorrect.
> ------------------------------------------------------------
>
> Key: MATH-1507
> URL: https://issues.apache.org/jira/browse/MATH-1507
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 3.6.1
> Reporter: Baljit Singh
> Priority: Major
>
> Let's say there is a circle on a spherical surface.
> * The circle center is given by S2Point(theta=-0.6981, phi=0.87266). The radius is irrelevant.
> * Let's discretize this circle into a polygon with 100 edges. Let's make the orientation {color:#ff0000}clockwise{color}.
> * Since its a clockwise circle, from symmetry, we know that the barycenter would be around S2Point(theta=2.44346, phi=2.268928), which is just the reverse of the normal vector at the circle center.
> * Using SphericalPolygonsSet, the calculated barycenter is S2Point(theta=2.4922, phi=0.69889).
>
> A few things I've already tested:
> * For counterclockwise, the result is correct.
> * The perimeter and surface area of the polygon is correct for both counterclockwise and clockwise.
> * The SphericalPolygonsSet barycenter seems to be a function of the circle radius. From symmetry, we know that there should be no dependence on the circle radius.
> * The theta is kind of close. However, the phi is off about pi/2.
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