toasty tile-allsky

The tile-allsky command takes a single image representing a full sphere and samples it into a TOAST tiling.

Usage

toasty tile-allsky
   [standard image-loading options]
   [--placeholder-thumbnail]
   [--outdir DIR]
   [--name NAME]
   [--projection TYPE]
   [--parallelism FACTOR]
   {IMAGE-PATH}
   {TOAST-DEPTH}

See the Standard image-loading options section for documentation on those options.

The IMAGE-PATH argument gives the filename of the input image. Its projection onto the sphere should be specified with the --projection option.

The TOAST-DEPTH argument specifies the resolution level of the TOAST pixelization that will be generated. A depth of 0 means that the image will be sampled onto a single 256×256 tile, each pixel in the tile having an angular size of about 0.6 deg². A depth of 1 means that the image will be sampled onto four tiles, for a total resolution of 512×512 and an average pixel area of 0.16 deg². A depth of 8 means that there will be 65,536 tiles and 4.3 billion pixels, with an average pixel area of about (11 arcsec)². The appropriate choice of the depth depends on your application.

The --outdir DIR option specifies where the output data should be written. If unspecified, the data root will be the current directory.

The --name NAME option specifies the descriptive name for the imagery to be embedded inside the output WTML file. It defaults to “Toasty”.

The --projection TYPE option specifies how the surface of the sphere is mapped on to the image. Allowed types are:

  • plate-carree (the default) — the image uses a “plate carrée”, AKA equirectangular or geographic, projection. The image will typically be about twice as wide as it is tall. Interpreted as a sky image, the north celestial pole is at the top of the image, RA = Dec = 0 is at the image center, and RA increases to the left.

  • plate-carree-galactic — like the above, but the image is in Galactic coordinates rather than (celestial) equatorial. This is often the case for all-sky astronomical press release images.

  • plate-carree-ecliptic — like the above, but the image is in barycentric true ecliptic coordinates rather than (celestial) equatorial.

  • plate-carree-planet — like the above, but the image is that of a planet and so the sense of the longitude/RA axis is inverted. Longitude increases to the right. This is the format in which planetary maps are typically represented. If you use this option when you should have used plate-carree, or vice versa, your map come out flipped horizontally.

If the --placeholder-thumbnail argument is given, an all-black placeholder thumbnail will be created. Otherwise, the thumbnail will be created by downsampling the input image. This operation can actually be the most memory-intensive part of the process, and can yield poor results with mostly-empty images. You can avoid this by using this argument and then invoking toasty make-thumbnail with a better-suited input image.

The --parallelism FACTOR argument specifies the level of parallism to use. On operating systems that support parallel processing, the default is to use all CPUs. To disable parallel processing, explicitly specify a factor of 1.

Notes

This command will create the highest-resolution tile layer, corresponding to the DEPTH argument, and emit an index_rel.wtml file containing projection information and template metadata.

Currently, parallel processing is only supported on the Linux operating system, because fork()-based multiprocessing is required. MacOS should support this, but there is currently (as of Python 3.8) a bug preventing that.