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GEO Search Polygon using MYSQL

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    GEO Search Polygon using MYSQL

    I built a grid to search my mysql db for addresses based on a polygon. All the video's show alpha selecting only items within polygon. When I do a polygon search, alpha appears to select everything within the rectangle of the outer most points. A radius search work fine and only selects items within the circle. Is this a mysql issue (I have heard that mysql cannot do exact polygons but I am not sure)?

    I am using mysql version 5.5. I have attached an example of the results of a polygon search (a triangle and almost all of selected items are outside the polygon).
    map.JPG

    #2
    Re: GEO Search Polygon using MYSQL

    You need to add a Point in Polygon test.
    I've done this using something similar to the technique described in this article.

    See http://graphics.cs.ucdavis.edu/~okre...InPolygon.html
    Bob Moore


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      #3
      Re: GEO Search Polygon using MYSQL

      Thanks Bob,

      Interesting mathematical technique and elegant. Base on your responce, I assume the problem I am having is a limitation of Mysql. My research over the weekend to try and solve this problem pointed to the fact that Mysql only supports MBR search which as I understand it is the rectangle formed but the outer most points.

      To use this point test technique, I assume that I would have to filter the records on one of the events "cansearch or aftersearch or onfiltercompute or onsqlselect". My thought process is to select records based on the current search and then filter the records based ony the point in polygon test. Sounds like a fun problem to solve.

      Comment


        #4
        Re: GEO Search Polygon using MYSQL

        Originally posted by Bob Moore View Post
        You need to add a Point in Polygon test.
        I've done this using something similar to the technique described in this article.

        See http://graphics.cs.ucdavis.edu/~okre...InPolygon.html

        Comment


          #5
          Re: GEO Search Polygon using MYSQL

          Hi Bob,

          I use MS sql with Polygon for various testing and very happy with the result.
          I like the idea very much.

          I would have wish to see a simple video :

          one of the most common thing most of us trying to do is to show customer location(s) on map
          relative to our offices for example and also showing coverage, which customer being taking cared by which office.

          what i have been doing is to have 2 seperate sql tables.

          * first is the ordinary customer table contain address, coordinates and locations
          * second a customerX table with similar structure and filled it with our office address, city, coordinates & Geolocation
          on the second table set to use circle on the map marker, i set my radius to 100"km"
          * then join the 2 tables together to make it like a single table


          * then create an alpha alternative view based on that newly combined table
          * now when i run the alternate view, i have a perfect picture showing all my customers and my office with a big circle
          I even place colour blue to indicate as our branch office, green being our main office etc
          these are parameter we set in the alternate view


          Having said that, is there anyway to achieve the similar thing with Polygons ?


          * how to save these polygon(s) point/marker to a table and apply them for future reference (re-search)
          * can we have multiple set of polygons on a map ?

          appreciate a feedback from everyone.

          thanks

          Ken Tjia
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