Feature request: generation of HiPS tiles

[tboch]

Currently, the library generates FITS or JPEG cutouts from HiPS tiles. It would be nice to have a Python-based generator of HiPS tiles, along the line of what Hipsgen currently does.

I wonder if this should be proposed as a separate package.

This issue is currently meant as a reminder for myself.

[cdeil]

That would be wonderful to have.

I wanted to do this for my specific application of making HiPS for all-sky Fermi-LAT images, but got stuck at the time (see attempt here). Apart from filling the HiPS pixels correctly, i.e. getting the basic functionality to work, a major question is what inputs to take and if / how to re-use http://reproject.readthedocs.io/ and http://healpix.readthedocs.io/ . Maybe making it work for a single HEALPix as input could be a first milestone, and then the complex case of taking many WCS-based images and processing them in a CPU and memory-efficient way like Hipsgen does could be a second step?

I wonder if this should be proposed as a separate package.

I would propose to include the functionality in this package.
(more packages is harder to discover / install for users and to maintain for developers)

[tboch]

@cdeil good to hear you also think this is a good idea.

I agree the first step would be to be able to generate a HiPS tile (given a tile order, tile number and tile size in pixels) from a FITS image with WCS.

[cdeil]

I agree the first step would be to be able to generate a HiPS tile (given a tile order, number and size) from a FITS image with WCS.

I was thinking generate HiPS from HEALPix first.

The way to generate HiPS from WCS is by resampling the WCS image to HEALPix and then to fill the HiPS pixels from a HEALPix pixel list, so the HiPS from HEALPix needs to be there anyways to make WCS work, no?

But if you plan to implement the feature for WCS maps (which most people have / want), then it doesn't matter so much what parts you implement first ...

As soon as something is available, I'd be eager to try it out for the images I have (mostly Galactic plane survey WCS images or all-sky HEALPix images that fit in memory, i.e. have sizes ranging from 1 MB to 1 GB.

[tboch]

I was thinking generate HiPS from HEALPix first.

The way to generate HiPS from WCS is by resampling the WCS image to HEALPix and then to fill the HiPS pixels from a HEALPix pixel list, so the HiPS from HEALPix needs to be there anyways to make WCS work, no?

Oh, I see. Indeed, generating a HiPS from a HEALPix file is a needed first step as to learn how to map HEALPix pixels to HiPS tiles. So, yes, let's start with this, it should be more straightforward than converting WCS maps to HiPS.