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https://issues.apache.org/jira/browse/LUCENE-8220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16412923#comment-16412923
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Karl Wright commented on LUCENE-8220:
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[~ivera], I now understand why the GeoConcavePolygon construction failed: my
check for whether a usable tiling had been found or not was in the wrong place.
So that mystery is cleared up, and I'll commit new code right now to address
that. But the tiling does not complete still with the right change, because
the only choices for edges to split the (non-concave) polygon all indeed yield
effectively colinear edges in this example. Indeed, I agree this is
theoretically possible during the tiling process whenever a new edge is created.
Polygons with very-close-together edge points that nevertheless cover
significant area are susceptible to this issue. In order for the tiling to
work, edges that are created for tiling must be labeled "internal", and we must
use exactly the same edge for both tiles that the edge is involved with. It
looks like your earlier patches achieve that by just making sure we don't pick
a tiling that doesn't work. Am I correct in this?
I'm beginning to at least understand the philosophy behind keeping "extended
edges" around. I'm still unsure that has the potential to solve the general
problem, though.
> GeoPolygon factory still shows problems with coplanar points
> ------------------------------------------------------------
>
> Key: LUCENE-8220
> URL: https://issues.apache.org/jira/browse/LUCENE-8220
> Project: Lucene - Core
> Issue Type: Bug
> Components: modules/spatial3d
> Reporter: Ignacio Vera
> Assignee: Karl Wright
> Priority: Major
> Attachments: concave.jpg, concaveWithTiling.jpg,
> coplanarity-test.patch, factory.patch
>
>
> The attached patch contains two polygons that still shows problems with
> co-planar points. To better explain the issue I attached some images:
> 1) concave.jpg: This is the polygon we want to build. Note that we want to
> build the concave part, therefore the blue part is actually not part of the
> shape and the white part is the area cover by the shape.
> 2) concaveWithTiling.jpg: The algorithm of the polygon factory tries to tile
> the polygon using convex polygons. In our case it creates the three colored
> polygons on the image. What it remains is a concave polygon.
> The problem with this polygon is that the right edge of the concave polygon
> contains co-planar points. These points cannot be merged into a single plane
> because they have different properties (internal edges or shape edges).
> Because GeoConvexPolygon and GeoConcavePolygon cannot handle polygons with
> co-planar points, the polygon cannot be built.
> [~kwri...@metacarta.com], Is it possible to make this polygons support such
> an extreme case?
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