CODEWITHSUNDEEP
mongodbgeolocationmongoosegeospatial
ddibiase
ddibiase

Reputation: 1502

Mongo geolocation using $near and 2d index not being accurate

I've written an application that finds local establishments and delivers them via a RESTful API. My stack is: express, express-resource and mongoose. Here is a sample of my model:

var PlaceSchema = new mongoose.Schema(
    {
        name: {
            type: String,
            required: true
        },
        geolocation: {
            lat: Number,
            lng: Number
        },
        address: {
            type: String
        }
    }
);
PlaceSchema.index({
    geolocation: '2d'
});

I've checked a few times and my lon/lat values are being correctly stored in the db, so there aren't any data errors.

Then I run the query to grab the data with the specific query values:

mongoose.connection.db.executeDbCommand(
    {
        geoNear: 'places',
        near: [
            parseFloat(req.body.lat),
            parseFloat(req.body.lng)
        ],
        num: limit,
        query: {
            // Some additional queries that
            // don't impact the geo results.
        },
        spherical: true,
        distanceMultiplier: 6371, // converting results to km
        maxDistance: distance / 6371,
    },
    function(err, result)
    {
        res.send(200, {
            status: true,
            data:   theaters
        });
    }
);

There are a few issues with the results that it's returning: a) the calculation in km is really wrong. In most cases there's a 6-7km difference, but it varies, b) places that are closer are appearing farther than other places.

I'm using the direct mongoose query because it will return the calculated distance (which I require for my API returns). Switching to the mongoose find method apparently wouldn't let me gain access to this data.

Wondering if my index is perhaps wrong? Should it be 2dsphere instead? The documentation in that regard is slightly confusing, but most of the examples I see use just 2d.

Thanks a bunch!

Upvotes: 1

Views: 4441

Answers (1)

Asya Kamsky
Asya Kamsky

Reputation: 42342

No matter what type of geospatial indexing you use in MongoDB, you always must store longitude first and then latitude.

From http://docs.mongodb.org/manual/core/2d/#store-points-on-a-2d-plane and multiple other places in the docs:

Whether as an array or document, if you use longitude and latitude, store coordinates in this order: longitude, latitude.

Upvotes: 9

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