Running bounding-box queries with Google Maps

Question

I am working on a google map application, to display the items that are listed in the selected rectangular area. Below image give you some understanding.

Based on the co-ordinates (topLeft,bottomRight), i am running bounding box query to find the items in mongo db. But it always returns the this error when running the box queries

 Error: $box needs 2 fields (bottomLeft,topRight)

I know that i have passed topLeft,bottomRight points instead the mongo expected one (bottomLeft,topRight).

How do I calculate the bottomLeft,topRight values based on the co-ordinates from Google Maps?

This is the actual value i got trouble with

bound_box = [[80.22050443383796, 13.051049734963444], [80.2393871853028, 13.043106313697518]]]

and ruby code for finding bounding box values in mongo db

items = Item.where(:loc => {"$within" => {"$box" => [bound_box]}},
                              :category => BSON::ObjectId(cat), :sub_category => BSON::ObjectId(sub)).order_by(:created_at => :desc).skip(@current_page * 5).limit(5).paginate

this is the line giving problem

items = Item.where(:loc => {"$within" => {"$box" => [bound_box]}})

which is similar to the mongodb query

 db.items.find({"loc" : {"$within" : {"$box" : bound_box}}})

Answer 1

If your coordinates are y,x formatted, and you have :

• topLeft : 42,10
• bottomRight : 31,21

then, to calculate bottomLeft, you get the y from bottomRight and get the x from topLeft

and to calculate topRight, , you get the y from topLeft and get the x from bottomRight :

• bottomLeft : 31,10
• topRight : 42,21

In case it is not clear enough, just take a pen and a piece of paper and draw it!