CDS (Strasbourg astronomical Data Center) celebrates in 2022 the 50th anniversary of its creation. 2022 also marks the 30th anniversary of the start of the Aladin project.
The original mission of the project - a sky atlas providing access to reference image surveys, enabling comparison of multi-wavelength data, cross-identification of sources - still holds strong. It it now fully supported by the HiPS (Hierarchical Progressive Survey) format.

We want to take the opportunity of this 30th anniversary to provide with a comprehensive summary of the HiPS ecosystem that CDS and its close partners (ESO, ESA, STScI) have built in the last decade, and which allows the creation, publication, visualisation and scientific exploitation of HiPS datasets.

As of July 1st 2022, the HiPS network is serving more than 1,000 HiPS with a total volume of 400TB and 300,000 billion pixels. Available HiPS are quite diverse, going from all-sky surveys (AllWISE, Integral, DSS, ...) to pointed observations (XMM-Newton, HST, HSC, Spitzer, ...), covering the whole electromagnetic spectrum and with a large variety of angular resolution.
HiPS is a container not only for pixel data, it is used to serve efficiently gravitational waves probability maps (LIGO/VIRGO), fluxes maps, density maps for VizieR catalogues, data cubes, but also large catalogues as the recent Gaia DR3 main table for instance.
HiPS have also been created for planetary surface data.

The large majority of the available HiPS images have been generated with the field-proven Hipsgen tool which was used notably to create HiPS for individual PanSTARRS bands (three quarter of the sky at 250mas/pixel resolution) in 16 days on a single server, for a total of 40 TB of FITS tiles.
The Montage toolkit, developed by IPAC, is also capable of generating HiPS individual tiles.

A network of 24 HiPS nodes is in use for distribution of the HiPS data, ensuring redundancy and good access time around the world.

HiPS data can be consumed by a dozen of existing clients: heavy clients (KStar, Stellarium, Aladin Desktop), web clients (Aladin Lite, World Wide Telescope, HscMap, Firefly) in various contexts: scientific purpose (with access to pixel real values), visualisation, amateur astronomy but also for EPO with the recent HiPS support in the Digistar planetarium control software.
Aladin Lite, developed at CDS, has been implemented in more than 50 professional astronomy websites and is being endorsed by ESA and ESO portals to explore and access their archival data.Version 3, currently in beta test, will offer all-sky projections, coordinates grid display, access to real pixel value (FITS tiles) and improved display thanks to GPU-based rendering.

HiPS is a FAIR (Findable, Accessible, Interoperable, Reusable) product: the HiPS protocol has been endorsed by the IVOA (International Virtual Observatory Alliance) and relies on proven existing standards (FITS, WCS, HEALPix). Individual HiPS are findable as resources in VO registries. As the data are sampled in a common space grid, they can be easily composed and reused, as shows for instance the hips2fits service which provides arbitrary FITS cutouts for any published HiPS.

The HiPS format itself has proven to be quite efficient and resilient to high load: in the hours following the release of the first JWST images, CDS servers have recorded more than 30 million requests on average (coming from 100,000 different IPs) with peaks at 1,500 requests per second.

We will conclude our presentation with an overview of the perspectives: access to HiPS and services related to large data cubes (in the context of SKA) and SED (Spectrum Energy Distribution) generation from photometric-calibrated HiPS.