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 = 43var phi = Numberprocessargv2 / 180 * MathPIvar theta = Numberprocessargv3 / 180 * MathPIvar out = healpixconsole
output:
$ node lonlat2xy.js -148 65
-2.476485479234211 -1.1544044416499766
x/y to lon/lat
var healpix = 43var PI = MathPIvar x = Numberprocessargv2var y = Numberprocessargv3var out = healpixconsole
$ node xy2lonlatjs -2476485479234211 -11544044416499766-14800000000000003 -65
api
var 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