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POFind how many (googlemap) polygons near x distance of a point
 

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  1. POFind how many (googlemap) polygons near x distance of a point
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    <p>I'm working on a MYSQL/PHP system where I have the following:</p> <p>-- a set of latitude, longitude in the form of (lat,lng) stored as text format : (lat1,lng1)#(lat2,lng2)#(lat3,lng3) etc. which is basically a polygon drawn over a googlemap instance stored in the database. </p> <p>-- a table which stores in a field - a point's coordinates P(plat,plng) which is basically a point where a device is stationed</p> <p>I need to figure out how many polygons from the first table are within a distance of X kilometers from the point P essentially using MYSQL.</p> <p>I have come across quite a few Google Map libraries regarding this already, but I intend to resolve this by the quickest method possible - which I assume is via a MYSQL query. </p> <p>Can anyone please please shed some light regarding this?</p> <hr> <p>I've so far consulted a few examples on geospatial querying - and come up with this :</p> <pre><code> SELECT user_id, latitude, longitude, GeomFromText( "POINT(CONCAT_WS(' ',latitude,longitude))" ) AS point, Contains( GeomFromText( 'POLYGON(-26.167918065075458 28.10680389404297, - 26.187020810321858 28.091354370117188, -26.199805575765794 28.125,-26.181937320958628 28.150405883789062, -26.160676690299308 28.13220977783203, -26.167918065075458 28.10680389404297)' ) , GEOMFromText( "POINT(CONCAT_WS(' ',latitude,longitude))" ) ) FROM user_location </code></pre> <p>But the problem is it shows a record with lat: -26.136230, long: 28.338850 as well which is way off the polygon's boundaries. Can anyone please guide?</p>
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    1. CONote that a "polygon" on the Earth does not really form a polygon, it divides the earth into two parts. Which one is 'inside' and which is 'outside'? If you treat Lat-Long as a cartesian coordinate system, what happens if your polygons cover the N or S poles?
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