geomodeljs v0.0.1

geomodel.js

This library is an implementation of the Geomodel/Geocell concept.

A geocell is a hexadecimal string that defines a two dimensional rectangular region inside the -90,90 x -180,180 latitude/longitude space. A geocell's 'resolution' is its length. For most practical purposes, at high resolutions, geocells can be treated as single points.

Much like geohashes (see http://en.wikipedia.org/wiki/Geohash), geocells are hierarchical, in that any prefix of a geocell is considered its ancestor, with geocell:-1 being geocell's immediate parent cell.

To calculate the rectangle of a given geocell string, first divide the -90,90 x -180,180 latitude/longitude space evenly into a 4x4 grid like so:

NOTE: The point (0, 0) is at the intersection of grid cells 3, 6, 9 and c. And, for example, cell 7 should be the sub-rectangle from (-45, 90) to (0, 180).

Calculate the sub-rectangle for the first character of the geocell string and re-divide this sub-rectangle into another 4x4 grid. For example, if the geocell string is '78a', we will re-divide the sub-rectangle like so:

Continue to re-divide into sub-rectangles and 4x4 grids until the entire geocell string has been exhausted. The final sub-rectangle is the rectangular region for the geocell.

Usage

Create a Geomodel instance:

var geomodel = require('geomodel').create_geomodel();

var hash = geomodel.compute_hash(lat, lon, hash_size);
var hash2 = geomodel.compute_hash(lat, lon); // hash_size = 8 (default)

var box = geomodel.compute_box(hash);

Sample output:

> geomodel.compute_hash(47, 29)
'e118e3d5'
> geomodel.compute_hash(47, 29, 16)
'e118e3d518e3d518'
> geomodel.compute_box("e118e3d5")
{ northEast: { lat: 47.00225830078125, lon: 29.00390625 },
  southWest:
   { lat: 46.99951171875,
     lon: 28.9984130859375 },
  getNorth: [Function],
  getSouth: [Function],
  getWest: [Function],
  getEast: [Function] }
>

For detailed usage see test/index.coffee

Testing

For testing you need to install nodeunit module:

# npm install nodeunit -g
# cd test & nodeunit index.coffee