Question

MongoDB has a very nice Geospatial Indexing feature. How can I use it in Rails with Mongoid?

Answer 1

You can define geo indexes like this in mongoid

class Item
  include Mongoid::Document

  field :loc, :type => Array

  index(
      [
          [:loc, Mongo::GEO2D]             
      ], background: true

  )
end

And for queries

$near command (without maxDistance)

 location = [80.24958300000003, 13.060422]
 items = Item.where(:loc => {"$near" => location})

$near command (with maxDistance)

 distance = 10 #km
 location = [80.24958300000003, 13.060422]
 items = Item.where(:loc => {"$near" => location , '$maxDistance' => distance.fdiv(111.12)})

Convert distance by 111.12 (one degree is approximately 111.12 kilometers) when using km, or leave distance as it is on using degree

$centerSphere / $nearSphere queries

location = [80.24958300000003, 13.060422]
items = Item.where(:loc => {"$within" => {"$centerSphere" => [location, (distance.fdiv(6371) )]}})

This will find the items within the 10 km radius. Here we need to convert the distance/6371(earth radius) to get it work with km.

$box (bounding box queries)

 first_loc = [80.24958300000003, 13.060422]
 second_loc = [81.24958300000003, 12.060422]
 items = Item.where(:loc => {"$within" => {"$box" => [first_loc, second_loc]}})

This will help you to find the items within the given bounding box.