level-places

level-places

Store and retrieve places near a lat/long pair, using leveldb.

Usage

Given a location, get all the nearby places, starting with the nearest one:

var level = require('level');
var Places = require('level-places');

var places = Places(level(__dirname + '/db'));

places.add('Kaufbeuren', 47.8800, 10.6225);
places.add('New York', 40.7142, -74.0064);

places.createReadStream(47.8838, 10.6171, { limit: 1 })
  .on('data', console.log);
  // => "Kaufbeuren"

How it works

Lat/long pairs are serialized into geohashes. The geohash for (47.8800, 10.6225) for example is u0x83sr14nyj. In order to query places efficiently this makes use of the fact that geohashes of geographically adjacent places start with the same characters, so they sort well.

When finding places near (47.8800, 10.6225)/u0x83sr14nyj, level-places queries its database using those queues one after another:

• u0x83sr14nyj
• u0x83sr14ny
• u0x83sr14n
• u0x83sr14
• u0x83sr1
• u0x83sr
• u0x83s
• u0x8
• u0x
• u0
• u
• ``

Additionally a random string is appended to allow multiple places per key.

Every place that is found and hasn't already been emitted will be. So, places are stored redundantly under those segments of their geohash. When a limit is given and it is reached, or you call stream.end(), level-store stops going further down the list.

API

Places(db)

Return a level-places instance that uses db for its storage, which needs to be an instance of levelup.

If you want to store other data in db, use level-sublevel to pass a subsection of your database.

Places#add(place, latitude, longitude[, fn])

Places#add(place, { latitude, longitude }[, fn])

Add place to the given lat/long pair. place can be of any type that JSON.stringify accepts. Optionally call fn as soon as the place was saved to the db.

Instead of passing latitude and longitude as seperate arguments you can also pass an object containing both.

Places#createReadStream(latitude, longitude[, options])

Create a readable stream that emits places around the provided lat/long pair, starting with the nearest one.

Possible options are:

• limit: Limit the result set to x places.

Installation

With npm do

$ npm install level-places

License

Copyright (c) 2013 Julian Gruber <[e-mail]>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.