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Posted to dev@lucene.apache.org by "Karl Wright (JIRA)" <ji...@apache.org> on 2017/09/24 12:40:00 UTC
[jira] [Comment Edited] (LUCENE-7970) Add a Geo3d shape that models
an exact circle, even when the planet model is not a sphere
[ https://issues.apache.org/jira/browse/LUCENE-7970?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16178177#comment-16178177 ]
Karl Wright edited comment on LUCENE-7970 at 9/24/17 12:39 PM:
---------------------------------------------------------------
[~ivera] The splitting algorithm described above yields the following number of planes for WGS84, where the first number reported is for the circle centered at lat = 0, and the last is the circle centered at lat = Math.PI * 0.5. So, to hit full accuracy, the number of planes is probably too high to be practical:
{code}
[junit4] 1> Number of planes needed: 1536
[junit4] 1> Number of planes needed: 1534
[junit4] 1> Number of planes needed: 1518
[junit4] 1> Number of planes needed: 1506
[junit4] 1> Number of planes needed: 1482
[junit4] 1> Number of planes needed: 2
{code}
However, if we allow the user to determine the level of accuracy, and (for instance) the user chooses an accuracy level of 1 meter or so, then it may well be a different story. Trying that out next.
Turns out that 1M accuracy isn't prohibitive at all:
{code}
[junit4] 1> Number of planes needed: 14
[junit4] 1> Number of planes needed: 14
[junit4] 1> Number of planes needed: 14
[junit4] 1> Number of planes needed: 14
[junit4] 1> Number of planes needed: 14
[junit4] 1> Number of planes needed: 2
{code}
was (Author: kwright@metacarta.com):
[~ivera] The splitting algorithm described above yields the following number of planes for WGS84, where the first number reported is for the circle centered at lat = 0, and the last is the circle centered at lat = Math.PI * 0.5. So, to hit full accuracy, the number of planes is probably too high to be practical:
{code}
[junit4] 1> Number of planes needed: 1536
[junit4] 1> Number of planes needed: 1534
[junit4] 1> Number of planes needed: 1518
[junit4] 1> Number of planes needed: 1506
[junit4] 1> Number of planes needed: 1482
[junit4] 1> Number of planes needed: 2
{code}
However, if we allow the user to determine the level of accuracy, and (for instance) the user chooses an accuracy level of 1 meter or so, then it may well be a different story. Trying that out next.
> Add a Geo3d shape that models an exact circle, even when the planet model is not a sphere
> -----------------------------------------------------------------------------------------
>
> Key: LUCENE-7970
> URL: https://issues.apache.org/jira/browse/LUCENE-7970
> Project: Lucene - Core
> Issue Type: Improvement
> Components: modules/spatial3d
> Reporter: Ignacio Vera
> Assignee: Karl Wright
> Attachments: LUCENE_7970.patch, LUCENE-7970.patch, LUCENE-7970-proposed.patch, LUCENE-7970_testBearingPoint.patch
>
>
> Hi [~Karl wright],
> How circles are currently build do not behave very well when the planet model is not an sphere. when you are close to the border in WGS84 you might get false positves or false negatives when checking if a point is WITHIN. I think the reason is how the points to generate the circle plane are generated which assumes a sphere.
> My proposal is the following:
> Add a new method to PlanetModel:
> public GeoPoint pointOnBearing(GeoPoint from, double dist, double bearing);
> Which uses and algorithm that takes into account that the planet might not be spherical. For example Vincenty's formulae (https://en.wikipedia.org/wiki/Vincenty%27s_formulae).
> Use this method to generate the points for the circle plane. My experiments shows that this approach removes false negatives in WGS84 meanwhile it works nicely in the Sphere.
> Does it make sense?
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