mongodb check if point is in polygon

Question

mongo 2.6

I have some amount of stored polygons. And I have a point. I what to know if this point fits any of stored polygons

document example

{ ..., "polygons" : [ [ 17.60083012593064, 78.18557739257812 ], [ 17.16834652544664, 78.19381713867188 ], [ 17.17490690610013, 78.739013671875 ], [ 17.613919673106714, 78.73489379882812 ] ], ... }

There is nearly the same question already Mongodb : Check if a point is inside a stored polygon. But it is not working for me - this query has to give at least one result(the one in example) - but it does not.

db.areas.find( { polygons : { $geoIntersects : { $geometry : {type:"Point",coordinates:[17.3734, 78.4738]} } } } )

Actually if I chose a point on a border of any polygon - it does.

$geoWithin method has to do the work as mondodb documentation says.

but any of these queries do not work

db.areas.find( { polygons : { $geoWithin : { $geometry : {type:"Point",coordinates:[17.3734, 78.4738]} } } } ) - not supported with provided geometry

db.tradeareas.find( { polygons : { $geoWithin : { $geometry : {type:"Polygon",coordinates: inside_polygon} } } } ) - BadValue bad geo query

It seems I miss something but cant understand what and where.

I would be grateful for help.

Answer 1

It seems to be to do with the order. If you are using $geoWithin and you are trying to find points inside a polygon, the thing that is within is the field you are searching on. However, $geoIntersects works in either direction, so you can search for points inside polygons, or polygons containing points, eg:

db.geom.insert({
  "polygons": {
    "type":"Polygon",
    "coordinates": [[
      [ 17.60083012593064, 78.18557739257812],
      [ 17.16834652544664, 78.19381713867188],
      [ 17.17490690610013, 78.739013671875],
      [ 17.613919673106714, 78.73489379882812],
      [ 17.60083012593064, 78.18557739257812]
    ]]
  }
});

db.geom.find({
  polygons: {
    $geoIntersects: {
      $geometry: {
        "type": "Point",
        "coordinates": [17.3734, 78.4738]
      }
    }
  }
});

Also, note that, you need to repeat the first point of the polygon at the end. If you remove the final pair, you will get a $err:

Can't canonicalize query: BadValue bad geo query" error.

It seems that MongoDB allows you to insert invalid geometries and only complains when you try and add a 2dsphere index or do an intersects/within/near query, which, I suppose is reasonable, as GeoJSON can be valid JSON without being a valid geometry.