geo-tree

geo-tree library

Geo-tree library is a tool for working with map objects. The primary use-case is creating a set of map-related objects (i.e. each of them having its latitude, longitude and data), followed with a queries to find objects in given area (exact match / rectangular area / circle area).

The existing code we used for this purpose originally (that was part of (one of the many available) google map directives) was not performant enough (it scanned the whole set of objects sequentially each time), so our goal was to speed the find queries using some clever data structures and algorithms.

After some prototyping and testing, we decided to wrap our GeoTree implementation around red-black binary search trees using z-curve algorithm for converting 2D plane coordinates into scalar index (and using this index as the numeric key in underlaying red-black tree).

This way, the find() operation doesn't need to go through the whole list, but we can eliminate a lot of items for which we know in advance that we don't need to consider them based on provided search criteria.

So when using hundreds or thousands or even more objects in your map application and having performance issues, may find this library very useful.

Installation

$ npm i geo-tree

API

Constructor

The GeoTree constructor function is the only exported library symbol.
You require it as:

const GeoTree = require('geo-tree');

To create new empty set (tree), do:

const set = new GeoTree();

Insert

To insert geo-related items into the set, use insert() function. Each inserted item must have latitude lat, longitude lng, and associated data data.

Supported ranges:

• lat: -90.0 .. +90.0
• lng: -180.0 .. +180.0
• data: any value

Assume we want to insert:

lat: 48.85886, lng:  2.34706, data: 'Paris, France'
lat: 52.50754, lng: 13.42614, data: 'Berlin, Germany'
lat: 50.05967, lng: 14.46562, data: 'Prague, Czech Republic'

Function insert() can be invoked with single parameter: object

{
  lat: ...,
  lng: ...,
  data: ...
}

So you would invoke it 3 times to insert the above 3 items, inserting one each time, e.g. to insert Paris, you'd do:

set.insert({lat: 48.85886, lng: 2.34706, data: 'Paris, France'});

For bulk insert, you can pass an array of the above mentioned objects, they will be inserted sequentially. So to insert all 3 of them in one insert() invocation, you'd do:

set.insert([
  {lat: 48.85886, lng:  2.34706, data: 'Paris, France'},
  {lat: 52.50754, lng: 13.42614, data: 'Berlin, Germany'},
  {lat: 50.05967, lng: 14.46562, data: 'Prague, Czech Republic'}
]);

Last option is to pass lat, lng and data as 3 arguments to insert(), which will insert one item with associated coordinates and data. E.g. to insert Prague, you'd do:

set.insert(50.05967, 14.46562, 'Prague, Czech Republic');

There is no need to have unique lat, lng pairs when inserting the items.

Find

To find items based on some geographical relation, use find() function. The function returns array of data fields of inserted items.

The order in which you'll get the found items in the resulting array is determined by underlaying red-black tree, so do not expect to see the data fields to be in any specific order.

With no argument, i.e. set.find(), the function returns array of the data field of all the inserted items.

set.find();
// --> ['Prague, Czech Republic', 'Paris, France', 'Berlin, Germany']

Specifying single object argument {lat: ..., lng: ...}, the function returns data fields of items that match the position exactly.

set.find({lat: 48.85886, lng: 2.34706});
// --> ['Paris, France']

You can pass two lat/lng objects to find(), in which case it will return data fields of the items in rectangle defined by the two coordinates (the arguments are treated as two diagonal vertices of a rectangle).

set.find({lat: 45, lng: 0}, {lat: 55, lng: 14});
// --> ['Paris, France', 'Berlin, Germany']

Finally, you can pass one lat/lng object, a float number, and optionally a string. These parameters are making up a circle (with provided center and radius) in which you search for the items. If you don't provide the third string argument, the units for the provided radius value are native to latitude and longitude (i.e. angle degrees). If you want to specify different units for radius, select one of the following: m for meters, km for kilometers, yd for yards, and mi for miles. In case you pass any other string, it is ignored and the value is not converted.

set.find({lat: 51, lng: 14}, 2.0);
// --> ['Prague, Czech Republic', 'Berlin, Germany']

set.find({lat: 51, lng: 17}, 200.0, 'mi');
// --> ['Prague, Czech Republic', 'Berlin, Germany']

Iteration over all items

GeoTree supports forEach method to which you pass a callback that takes single argument. We iterate over all items in the set and invoke provided callback, passing data field of the item.

set.forEach(function(data) { console.log(data); });
/* prints to console:
     Paris, France
     Prague, Czech Republic
     Berlin, Germany
*/

Same as for the find() method: the order passed data items to the callback is determined by underlaying red-black tree structure, so do not expect to see the callbacks invoked in any particular order.

For debugging: dump

For debugging purposes and for the purposes of unit tests, there is dump() method that either prints the internal representation of the current stored set to the console (no argument, or falsey argument passed), or generates a string that describes the the tree (single truthy argument passed).

Working from source code

$ git clone [e-mail]:salsita/geo-tree.git
$ cd geo-tree
$ npm i
$ npm test

Eslint is used for linting the source code, and jest as the test runner. The test coverage report is stored in coverage directory after testing.

There are also two additional test files in test directory:

• benchmark.js: run it before you make changes to the source code, and then after, to see the performance impact of your change,
• test.js: playground for your new feature(s).

To run them, just do

$ node test/benchmark

and

$ node test/test

Change-log

• 1.0.1 (2017-11-03): Major rework of infrastructure (gulp no more, jest, eslint, ...)
• 0.1.4 (2014-10-27): Gulp build system replaced Grunt
• 0.1.3 (2014-10-21): Repo migrated from my private account to salsita account
• 0.1.2 (2014-10-12): Haversine function for radius verifications
• 0.1.1 (2014-09-16): support for m/km/yd/mi radius value for circle-search operation
• 0.1.0 (2014-09-04): initial version (insert, find and forEach operations)

MIT License

Copyright (c) 2014-2017 Salsita Software

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.