Problems with Lat / Long searches at minimum and maximum latitude and longitude

[Randy Tidd <rc...@tidd.cc>]

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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Re: Problems with Lat / Long searches at minimum and maximum latitude and longitude

[Michael McCandless <lu...@mikemccandless.com>]

Hi Randy,

Robert already replied to your previous email ... maybe you missed it?

Mike McCandless

http://blog.mikemccandless.com

On Sat, Jun 11, 2016 at 4:05 PM, Randy Tidd <rc...@tidd.cc> wrote:

> 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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