healpix
v1.0.0
Published
convert between lonlat and HEALPix coordinates
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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