healpix v1.0.0

healpix

convert between lonlat and HEALPix coordinates

HEALPix coordinates are an equal area projection very similar to cube mapping. This coordinate system is used heavily in cosmology, where equal-area and uniform point distribution are important for density comparisons and binning.

The HEALPix algorithm is described in the paper Mapping on the HEALPix grid

example

lon/lat to x/y

var healpix = require('healpix')(4,3)
var phi = Number(process.argv[2]) / 180 * Math.PI
var theta = Number(process.argv[3]) / 180 * Math.PI
var out = healpix.ang2xy([], phi, theta)
console.log(out.join(' '))

output:

$ node lonlat2xy.js -148 65
-2.476485479234211 -1.1544044416499766

x/y to lon/lat

var healpix = require('healpix')(4,3)
var PI = Math.PI
var x = Number(process.argv[2])
var y = Number(process.argv[3])
var out = healpix.xy2ang([], x, y)
console.log(out[0]*180/PI, out[1]*180/PI)

$ node xy2lonlat.js -2.476485479234211 -1.1544044416499766
-148.00000000000003 -65

api

var healpix = require('healpix')

var hp = healpix(H, K)

Create a healpix projection parameterized by H,K.

hp.ang2xy(out, phi, theta)

Calculate [x,y] on the healpix projection given:

• phi - longitude in radians
• theta - latitude in radians

Set [x,y] and return out.

hp.xy2ang(out, x, y)

Calculate [phi,theta] from [x,y] on the healpix projection.

Set [phi,theta] and return out.

install

npm install healpix

license

BSD