GeoJSON

Format for encoding geographic Data Structures

location : {
  "type" : "point",
  "coordinates" : [12.2, 13.1]
}

GeoJSON supports following geometries -
 - Point
 - MultiPoint
 - Polygon
 - MultiPolygon
 - LineString
 - MultiLineString

 - GeometryCollection
 - Feature
 - FeatureCollection

Geospatial Indexes 

2dsphere - support queries that calculate geometries on earth like spheres
     db.collection.createIndex( { <location field> : "2dsphere" } )
2d - support queries that calculate geometries in s 2D plane
     db.collection.createIndex( { <location field> : "2d" } )

These indexes can not cover a query.
These indexes can not be used in shard key.

Following geospatial operations are supported on sharded collections - 
  - $geoNear aggregation stage
  - > 4.0, $near and $nearSphere query operators

geoHaystack - optimised to return results over a small area. Improves performance of queries that use flat geometry. For queries using spherical geometry, better to use 2dSphere indexes. 
geoHaystack requires first field to be location. 
Creates buckets of documents from same geographic area to improve query performance. 
Each bucket contains all documents in specified proximity to a given latitude and longitude.
sparse by default. 

https://docs.mongodb.com/manual/tutorial/query-a-geohaystack-index/#geospatial-indexes-haystack-queries


Query Selectors

$geoIntersect - selects geometries that intersect with the given geometry
    2dSphere supports this. Does not require the geospatial index.

$geoWithin - selects geometries within bounding geometry. Both 2dSphere and 2d indexes support this
     $geometry, $centerSphere
   
     $centerSphere takes distance in radians.
     3963.2 miles - radius of earth. Divide the distance by this to get result in radians

$near - returns geospatial objects in proximity to point. Both 2dSphere and 2d indexes support this

$nearSphere - returns geospatial objects in proximity to a point on a sphere
Both 2dSphere and 2d indexes support this
      $geometry, $minDistance, $maxDistance


$geoNear - AggregationFramework
   - near .. GeoJSON point
   - spherical .. must be true if using a 2dSphere index
   - maxDistance, minDistance .. meters
   - distanceField
   - distanceMultiplier

1609.34 converts miles to meters

Geometry Specifiers -

$box - specifies a rectangular box using legacy coord pairs for $geoWithin. 2d index

$center - specifies a circle using legacy coord pairs for $geoWithin. 2d index

$centerSphere - specifies a circle using either legacy coord pairs or GeoJSON object with $geoWithin.
2d or 2dSphere index.

$geometry - specifies a geometry in GeoJSON format for search with geoSpatial operators.
uses EPSG:4326 as default Coordinate Reference System(CRS).

$geometry: {
   type: "<GeoJSON object type>",
   coordinates: [ <coordinates> ]
}

s.find({ "o": {$eq:"99e01530-4538-4e26-b834-0072011af7ed"},
         "t":{$gte: 0, $lte: 176829836394000 },
         "l": {$geoWithin:
                 {$geometry:
                    { type: "Polygon",
                         coordinates:[
                              [[59.907542457804084, 86.79600024595857],
                               [59.907542457804084, 80.64036540314555],
                               [66.908002791926265, 80.64036540314555],
                               [66.908002791926265, 86.79600024595857],
                               [59.907542457804084, 86.79600024595857]
                              ] 
                         ]
                    }
                 }
              }
       }

$maxDistance - specifies max distance in meters to limit the results of $near and $nearSphere.
2d and 2dSphere indexes.

$minDistance - specifies min distance in meters to limit the results of $near and $nearSphere.
2dSphere indexes only

$polygon - specifies polygon in legacy coord pairs for $geoWithin. uses planar geometry.
2d Index. Can even query without 2d Index.

$uniqueDocs - deprecated. modifies $geoWithin and $near queries to ensure that even a document that matches query multiple times, is returned only once.




https://docs.mongodb.com/manual/reference/operator/query-geospatial/