Photometric Conservation in HiPS Processing

The HiPS technology has originally been developed within the frame of the Aladin project in order to provide a progressive access to survey pixel data from AliSky view up to full resolution images. HiPS is currently entering an IVOA standardization process, the number of HiPS surveys has been rising steeply since its creation and is expected to keep growing. HiPS technology is strongly based on the HEALPix tessellation of the sky. As HiPS surveys are produced, original images are regridded onto HEALPix tiles and vice versa when the data are reprojected back on usual WCS FITS grids. As with any projection process, this may introduce systematic and random uncertainties in the projected data. In this poster the authors present results from different photometric conservation tests. Theses tests have estimated the photometric accuracy in large apertures between fluxes measured on original and HiPS images. Photometric uncertainties for point sources have also been estimated by comparing source extraction results as obtained with SExtractor on original images and on HiPS reprojected images.