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From Randy Tidd ...@tidd.cc>
Subject Problems with Lat / Long searches at minimum and maximum latitude and longitude
Date Sun, 12 Jun 2016 17:43:18 GMT
Thanks for the help you’ve already given me on getting search with LatLonPoint working, the
basics are working great and with great performance.

I did some testing on some edge cases and discovered that indexing and searching for points
at the minimum and maximum latitude and longitude are not working as I expected.  I’d appreciate
some feedback on this.

Take for example the point (0.0, 180.0) which is in the Pacific ocean at latitude = 0.0 and
longitude = 180.0.  If we create a grid of 9 points centered on this location (“tic tac
toe” layout) with an offset of 0.1 the coordinates would be:

(0.1, -179.9), (0.0, -179.9), (-0.1, -179.9), (0.1, 180.0), (0.0, 180.0), (-0.1, 180.0), (0.1,
179.9), (0.0, 179.9), (-0.1, 179.9)

The max longitude is 180, so if you move 0.1 degree east the next longitude is actually -179.9
rather than 180.1, it wraps around.

If I then create a square that encompasses these points using an offset of 1.0 (larger than
the 0.1 for the indexed points) that polygon would have these endpoints:

(-1.0, 179.0}, (1.0, 179.0), (1.0, -179.0), (-1.0, -179.0), (-1.0, 179.0)

The first and last point are the same so that this is a closed polygon.

When I index these points with LatLonPoint and do a search with LatLonPoint.newPolygonQuery()
it does not return any results, which isn’t what I expected. 

However, if I index a grid of points around (0.0, 0.0) and search with this polygon, they
are returned by this search, which I don’t believe is correct.  It is as if the search thinks
that the point (0.0, 0.0) is between the points (0.0, 179) and (0.0, -179) which I don’t
think is correct.  Longitude 0.0 and 180.0 are on opposite sides of the globe.

I see the same behavior with data centered at these points:

(90.0, -180.0)
(90.0, 0.0)
(90.0, 180.0)
(0.0, -180.0)
(0.0, 180.0)
(-90.0, -180.0)
(-90.0, 0.0)
(-90.0, 180.0)

However, using more “normal” points such as (44.4605, -110.8281) this test works fine.

So I’m wondering if there is a problem with the search handling polygons that span the latitude
and longitude boundaries, or if maybe I am just not thinking about this right to begin with.
 I can post sample code if that would be helpful.  Thanks for any assistance / input.

Randy


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