Library to build WorldWide Telescope TOAST tiles
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Library to build WorldWide Telescope TOAST tiles.


  • Required: python (2.6, 2.7, 3.2, or 3.3), numpy, cython, Pillow/PIL
  • Optional: astropy (for FITS IO), healpy (for HEALPIX data), pytest (for testing)


from toasty import toast
toast(sampler, depth, directory)


  • sampler is a function that takes 2D arrays of (lon, lat) as input, samples a dataset at these locations, and returns the resampled image
  • depth is the depth of the tile pyramid to create (4^d tiles are created at a depth of d)
  • directory is the path to create the hierarchy at

Toasty provides a few basic sampler functions:

  • healpix_sampler for sampling from healpix arrays
  • cartesian_sampler for sampling from cartesian-projections
  • normalizer for applying an intensity normalization after sampling


To toast an all-sky, Cartesian projection, 8 byte image:

from toasty import toast, cartesian_sampler
from import imread

data = imread('allsky.png')
sampler = cartesian_sampler(data)
output = 'toast'
depth = 8  # approximately 0.165"/pixel at highest resolution
toast(sampler, depth, output)

To apply a log-stretch to an all sky FITS image:

from toasty import toast, cartesian_sampler, normalizer
from import fits

data ='allsky.fits')[0].data
vmin, vmax = 100, 65535
scaling = 'log'
contrast = 1
sampler = normalizer(cartesian_sampler(data), vmin, vmax
                     scaling, bias, contrast)
output = 'toast'
depth = 8
toast(sampler, depth, output)

To perform a custom transformation

from toasty import toast
from import fits

data ='allsky.fits')[0].data

def sampler(x, y):
    x and y are arrays, giving the RA/Dec centers
    (in radians) for each pixel to extract
    ... code to extract a tile from `data` here ...

output = 'toast'
depth = 8
toast(sampler, depth, output)

See toasty.tile for documentation on these functions.

Using with WorldWide Telescope

To quickly preview a toast directory named test, navigate to the directory where test exists and run

python -m toasty.viewer test

This will start a web server, probably at (check the output for the actual address). Open this URL in a browser to get a quick look at the data.

For more information about using WorldWide Telescope with custom image data, see the official documentation. The function toasty.gen_wtml can generate the wtml information for images generated with toasty.

For an example of tiles generated with Toasty (originally from Aladin healpix images), see The ADS All Sky Survey. The code used to generate these images is here.